Wheels / Tires

* Wheel Construction and Basics
* Specific Wheels
* Restoring
* Widening / Adapting / Interchange
* Tires

Submit corrections and additions to this information to The Olds FAQ Compiler.



Wheel Construction and Basics


Hubcentric or Lugcentric

Wheels are classified as either "hubcentric", meaning the hub centres the wheel, or "lugcentric", meaning only the mounting lugs centre the wheel. As far as I know, all OEM wheels are hubcentric, and from an engineering standpoint this is the better method. However a number of aftermarket wheels are, in fact, lugcentric. So you probably can use your wheels on your car and not get in trouble. Just don't use any additional wheel-spacers between the hub and wheel, and don't use cheapo lug-nuts with heavily chromed stems - the nut shanks are often quite oval due to the uneven heavy chrome plating, and that means your wheel will end up slightly off centre in an unpredictable way depending on where the nuts end up after you finish torquing them. I bought my cheapo oval-shank nuts from Jegs, so I experienced this firsthand!

If you want extra security, ARP makes super-strong wheel studs which can replace your OEM ones and provide some additional safety margin.

[ Thanks to John Carri for this information. ]

Wheel Terminology

Check out http://www.rsracing.com/wheelstuff.html for some nice wheel terminology descriptions.

Backspacing is the dimension from the inboard edge of the rim to the backside of the bolt flange of the wheel (the surface which mates to the axle flange).

Offset is the difference between the centerline of the rim and this same bolt flange. Zero offset is defined as the condition where the bolt flange is exactly aligned with the center of the rim.

Negative offset is when the bolt flange is further inboard than the centerline (ie, deep dish wheels), while positive offset is when the bolt flange is further outboard than the centerline (ie, most FWD car wheels).

Feeble attempt at ASCII art follows:

         Inboard |               | Outboard
                  \_____________/ 
                 |       |       
  Backspacing----|<----->|
                         |          
  Bolt Flange----------->|      
                   ______|______       
                  /             \
                 |               |


      Centerline of Rim->|
                         |
         Inboard |       |       | Outboard
                  \_____________/ 
                      |  |       
  Negative Offset-----|<>|
                      |        
  Bolt Flange-------->|        
                   ___|_________       
                  /             \
                 |               |


      Centerline of Rim->|
                         |
         Inboard |       |       | Outboard
                  \_____________/ 
                         |  |     
  Positive Offset--------|<>|
                            |        
  Bolt Flange-------------->|        
                   _________|___       
                  /             \
                 |               |
[ Thanks to Joe Padavano, Mike Bloomer, Cliff Simpson for this information. ]

I measured some wheels and here are the backspacing measurements I came up with:

1970-74 SSII or III 14x7 4.25"
1975-77 SSIII 15x7 4.25"
1981-88 SSIII 14x6 3.5"
1987 442 Chrome 15x7 4"
?? Factory Steel 14x 3 7/8"
?? Factory Steel 15x ??

It's interesting that the 1987 442 chrome wheels appear to have the same outer rim as the 1975-77 SSIII (except for the chrome of course). The centers are welded in a slightly different location in the rim and this is the reason for the backspacing difference.

Some rims may have a 3.75 inch backspacing. I've never seen it on an Olds rim but there are many Camaro rallye rims with a 3.75 inch backspacing, some Olds might have that too.

[ Thanks to John Pajak for this information. ]

Drum vs Disc Wheels

When you say that your disc brake swap required 15" wheels, did you try the later (70-up) disc brake 14" wheels with the different contour on the rim? I don't know about the full-size cars, but the A-bodies definitely have 14" rims which will clear factory discs (but obviously not aftermarket discs like Baer). The problem is that up until the late 60s, drum brake cars received wheels which will not clear the caliper, but disc brake cars used a 14" wheel with a recontoured rim which provided more clearance on the backside for the caliper. Note that this is the case for plain steel wheels as well as the SSIs. I would guess that this is the case for the big cars as well.

Best to pick up SS1 wheels if you don't go for the aftermarket ones is swap meets. I bought mine for under $100 the set. They are very nice and I just had get some center caps and retainers. They come in disc clearing and non disc clearing versions and you have to make sure you buy the right ones. The ones that clear the disc open up real quick in the inside diameter, the ones that dont go narrow inside all the way to the inside edge of the rim where they will widen up about 2 inch off the edge. Hope this is not too confusing.

The early, all chrome SS Is will not fit, however the later SS Is which were painted and used the chrome trim rings will clear the disc brakes.

From the side if you cut the rim open it kinda looks like this:

Non disc brake SS I:
             _       _
              \_____/

outer side               inner side

               _____
              /     \
             -       -

Disc brake SS I:
             _   _____
              \_/

outer side               inner side

               _
              / \
             -   ------
[ Thanks to George cutlass@one.camd.lsu.edu, Joe Padavano for this information. ]


Specific Wheels


1950's Wheels

Have you tried going to some wrecking yards within your area? If not, I'd suggest that you go looking there for wheels. The same size wheels were used for quite a few years, 1960-1962 Oldsmobiles were all the same size and style of wheel, and 1963-1964 Oldsmobiles also had the same size wheels but their style was slightly different. The 1957-1959 Oldsmobiles had 14" wheels but I'm not sure how their style differed from the 1960-1964 wheels. I'm sure you should be able to find a few early 60's Oldsmobiles in local yards.

I'm not sure if you've already tried it, but there are radial inner tubes available in about 90 percent of the sizes currently on the road. That way you could keep your original steel wheels and get the radial ride.

A word of caution here -- use the narrow rims, not the wide ones as apparently they can rub inside the fender wells, particularly with a load on the car.

You can put radial tires on bias ply tube required rims, but they flex a lot. A friend of our did not get the newer rims, and was sorry 3X over -- he used radial tires on bias ply rims, and 3 of them split on him. They apparently cannot take the additional flexing of the radial tires.

[ Thanks to Cliff McFarlane, Dave Van Sant, Sherry Soball for this information. ]

Differences Among Super Stock Wheels

Compiler's note: My head was about to burst in trying to organize this information in a summary form and breakdown by wheel sytle. I did the best I could, but I'm sure there is some duplication.

The size is stamped on the center of the inside of the rim, along with other information, like "Made in Canada". Unless you are a stickler for manuracturing codes, SS IIs and SS IIIs are identical except for the paint. You can sandblast or strip the paint and change the color as needed.

A SS II/III is the traditional Olds wheel. You can order the "correct" paint from many of the Olds parts suppliers

Don't have any ordering sheets to go by, but my dealer SPECS books of the era say this:

Here are some pictures: http://www.flash.net/~texas442/wheels.html.

You can buy reproductions of SSI's and SSII's with or without the trim ring from Specialty Wheel and Wheels Vintique. They look 100% correct with the trim ring. Without the ring they look too much like a Magnum 500 wheel.

Another summary:
All SS IIs (and some SS IIIs) were bolt-on. All snap-in center wheels are SS IIIs. In addition, all 14x6 bolt-on center wheels are SS IIs (made in 68-69 only).

The only difference is paint: SS II is painted Agrent, SS III is painted body color.

Note, however, that many of these wheels have been repainted over time, so there may not be a sure way to tell (nor does it really matter, unless you are doing a concourse restoration and care about the date codes on the wheels). As I noted in a prior post, however, there are some sure calls:

14 x 6 with bolt-in centers are all SS IIs - Only made in 68-69 and all came from the factory in Argent. ('Course, I've got a set at home that are painted Ford Tangerine...it's a long story)

All snap-in center wheels are refered to as SS IIIs (actually, I'm not so sure about this in the G-body cars. Someone with better knowledge might have more correct info)

The early 70s bolt-in wheels were either called SS II or SS III depending on color.

All of the SS II and SS III wheels of any year will clear factory disc brakes. All came with 5 on 4 3/4" bolt circles. All the bolt-in centers are the same, but there are several variations of snap-in centers: the traditional, the cylindrical, the 442-logo, and the "starfish" (as used on the 77 Delta 88 pace cars). What am I forgetting?

Oh, I should probably give a passing mention to the SS III look-alike wheels used on the FWD Cutlass Ciera and Calais cars in the early 80s. I have no idea what these were called. Obviously, they don't fit the RWD cars.

Olds produced SS IIs and SS IIIs between 1968 and 1988 in various iterations. The dividing line is bolt-in centers vs. snap-in centers. Bolt-ins were made through 1974, in sizes 14x6, 14x7, and 15x7. Snap-ins were made in these same sizes and had other variations such as the chrome wheels of the 1980s and the various center designs (traditional, smooth round, "442", and the infamous "starfish"). There was also a FWD version used on the Cieras and N-body Calais in the 80s, though I don't know if there were referred to as SS IIIs or something else.

Basically, the 'Chrome Super Stock III Wheels', as per the 1984 Cutlass Ciera, Supreme and Calais showroom catalog, have the plastic (?) trim ring deleted and the whole wheel is plated with chrome. I believe the center caps are the same. I couldn't tell you about offset and all those dimensions, only that the chrome versions are 14x6.

The 80's Cutlasses came both ways, with body color (regular) SSIII's and chrome SSIII's. Actually, I've seen more chrome wheels on the G-Bodys than I have the body color SSIII's.

The spare tire hold down for the SS wheels is pretty much the same as for regular steel wheels. It is like a bent piece of steel rod which hooks into a loop spotwelded to the trunk floor and which has the other end threaded. The retaining nut looks something like a lug nut, but the internal tread is much smaller in diameter to mate with this rod.

[ Thanks to Mike Rothe, Jason Adcock, Joe Padavano for this information. ]

Balacing Super Stock Wheels

The problem with SSIII wheels is not the wheels themselves, but the people who balance them. Yes, everyone of them. MOST tire jockeys are minimum wage amateurs who don't know that it's tricky to mount SSIII's as well as SSII's on a balancer. The problem is, the center cone on those wheels are very small.

You have to clean the back of the wheel and put the large cup on the back of the wheel. In other words the balancer attaching order is such: big cup, wheel, very small cone, spinner. Most wheels are: appropriate size cone, wheel, big cup, spinner. The center of the rims are not always true to the rim because of the way that it sticks out. There is an adapter available to balance wheels by centering the stud holes. The problem is that these adapters are not cheap, and most tire shops do not have one. If you can find a shop that does that would be your best bet.

Tire guy's may do a set of SSIII's every few months while they do normal rims every day. You can tell just by watching the wheel whether they have it on straight. It will have a slight wobble if it's wrong. It will balance on the machine with very LARGE weights in that manner. But on the car, the tires are even more out of balance than with no weights at all.

Some important things to remember, mud in the rim will throw off balancing. Fix-a-flat will annihilate balancing. The beauty rings are not on the rim when balancing takes place and beauty rings are not balanced. The guy will roll his eyes, but if you can talk him into it ($), you can have him spin the wheel with the trim ring on, take it off to mount the weights, and replace it to re-check it. It DOES make a slight difference.

Most of all SUPERVISE. They hate it, but it is your right. If they won't let you, go somewhere else. When I was still in the business, I was the only one in my shop that could get SSIII's down to zero. I hated pulling of a REAL job to do it but if we wanted that customer to come back. It takes someone who cares what they are doing.

I did find a local store with a knowledgable person who owned a set of SSIIIs and was able to balance the wheels with a "back cone" balance where the rim is put on the machine with the back of the wheel facing the balance machine (instead of the front). The technician said that the wheels should balance fine this way and with new tires the total weights that are required for a proper balance shouldn't usually be more that 1.5 ounces total (for inside and outside). All 4 of my wheels required less than the expected 1.5 ounces total so they appear to be OK. Now, I've got a proper balance (finally) with some good tires and a smooth ride. Moral of the story:

1) ask for "back cone balance."
2) be suspicious of bad balance if you have large weights on your SSIIIs with good tires.
[ Thanks to Ed Binnix, Thomas Bartee for this information. ]
Static Balance
If you have chrome wheels, and hate ugly balance weights showing, you may want the wheels static balanced. Nothing worse than having ugly lead weights on the outside of the rims.

However, while having the balance weights on the outside may look ugly, it really is required to properly balance the wheel dynamically. Static balance only balances in the plane of the tire, which is certainly the largest imbalance effect, however a side-to-side imbalance will not be taken out this way and can still lead to a noticeable vibration. Obviously you have to make the decision for yourself - looks or balance.

Note that by no means am I saying that you'll always need weights on the outside. In many cases an acceptable balance can be obtained with inside weights only. I just wanted to point out that if the balancer says you need them on the outside, you have to decide which is more important. Of course, you could always try to get the tire guy to dismount the tire and rotate it on the rim to try and better match the two up.

[ Thanks to Ed Binnix, Thomas Bartee, Mark Tupper, Joe Padavano for this information. ]


Super Stock I

These are known as option "P05". It is a chrome wheel that looks like a Buick wheel. These all chrome (no trim ring) wheels were offered in 1965 through to 1969 in 14x6. The Part Number in 1966/1967 was 393822. You can identify this wheel by the number 795C stamped somewhere on the inside rim area. They do resemble Ford Magnum 500's. Almost all of these will not clear disc brakes. Early SS1 can be identified if they are stamped "795 C". An early '66 (first year offered) wheel will have shiny chrome spokes, not satin finish.

Early SS I's are stamped 795 JK (JK is a heavy duty designation found even on some steel wheels). In '66 the whole wheel was shiny chrome causing problems with the black paint sticking (note shiny spokes). Late in '66 they started blasting the center sections resulting in better paint adhesion (note "satin" like finish to spokes). For disc brake models, SS1's are stamped 810 JK. They have a visible additional "groove" in the rim.

Early style SS Is (without the trim ring) that fit disc brakes were produced. They are just very hard to find due to the fact that not many disc brake cars were produced. 15" SS I's will fit disc brake, but there will be some interference. The fix is simple. Just by file approx. 1/8" off the two outermost corners of the outermost brake pad. Don't know about 14" SSI's though.

In 1970 they were offered as a 14x7 but with a trim ring and sized to fit disc brakes. This option carried on through 1972. Instead of the "795" number stamped inside, they're "810". At a glace they look the same, most noticeable is an additional groove in the rim section.

The SS Is were not available with disc brakes until 1970 (the ones with the chrome rings). From the backside, if you compare a disc and non-disc wheel, the difference will be obvious. The rim on the inboard side will drop down towards the center of the rim almost immediately inboard of the tire bead on a non-disc rim, whereas a disc rim will continue towards the outside of the wheel for a while before dropping in towards the center (this, of course, to clear the calipers). Note that there were some of the disc-compatible SSIs made in 1971 (?) which were chrome also.

All chrome (no trim ring) SS I wheels were offered by Olds only in 1971 in 14x7 size. There are quite rare, only offered on the 1971 SX's. So there arent that many out there.

Most of the 14x7 SS I's you see will have the chrome trim ring. Today you can buy them from several wheel manufacturers who will prefer to sell you the all chrome version because it is less expensive than buying a wheel and trim ring combination.

[ Thanks to Kurt Shubert, Jim Chermack, Joe Padavano for this information. ]
Brent Cnvrt67@aol.com


Buick Super Stock I Look Alikes

The difference between the Olds SS I wheels and the Buick wheels is that if you put them side-by-side, you'll see that the Buick wheels really don't look like SSIs. The radial ribs are flat on the SS Is, but are concave on the Buicks. The SS Is are, in fact, identical to the Chevy "Magnum 500"-style wheels (sorry, I know Magnum 500 is the F*rd designation; don't know what the Chevy code is).

Buick's have no taper on the spokes. The Olds' spokes are wider at the edge than at the center.

There are also aftermarket SSI clones available (for serious $$) which are available painted or chrome and in sizes up to 15x10. I just saw these in the latest Coker catalog that came with the Oct Hemmings. Note that they were listed as Chevy wheels, but since you have to buy the center caps separately anyway, they can also be SSIs.

A mixture of Olds an Buick SS Is, say Olds on the car with a Buick spare, can be used, they will bolt up, but not look exactly correct.

[ Thanks to Charley Buehner, Joe Padavano for this information. ]


Super Stock II

The SS II wheels were used first in 1968, with a size of 14 x 6 (option code N71). For 1968, all SS IIs for the Cutlass/442 were painted grey, or what some call argent. There were no tin or chrome bezels around the holes in the wheels; the raised area was painted silver. This was for 1968 only. They used the same centers as later SS II and SS III wheels with the bolt on center cap.

There are NO SSII/III wheels with a 5" on 5 pattern.

The 14 x 7's were only used from 1970 to 1972. This, of course, excludes the 1969 H/O which had 15x7s and the 1973(?) and later 15x7 wheels. There was also a 13" wheel offered as option code N66. Don't know what years.

These will work with disc brakes.

[ Thanks to for this information. ]


Super Stock III

The Super Stock III wheels are exactly the same, 14 x 7, as the 1970-72 SS II wheels, except that they were painted the same color as the lower part of the car (option code N67 - chrome). Option N73 was the 13" variation in lower body color.

Both SS II and SS III came with chrome bezels around the five holes, and a 14" trim ring. They also have a hub center cap in the center of the wheel that has the Olds rocket symbol.

A chromed version of the Super Stock III wheels was offered from 1983-1988 and came in two sizes, 14 x 6 and 15 x 7. The 14" option code was N66 and N83 was the 15" option code. The N66 wheels were available on any RWD Cutlass from 1984-1988, except for the Hurst/Olds and 442. They had black painted insets and no pinstripe around the edge of the wheel. Center caps show a black background with the red rocket symbol in the middle. The N83 wheels came only with the high-performance Cutlasses (H/O, 442) from 1983-1987. The Hurst/Olds wheels had argent painted insets and a red pinstripe, whereas the 442 versions had gold painted insets and gold pinstripes. Also distinguishing the 442 wheels are the center caps, which read '442'. All wheels were of a two-piece design. They were chromed as separate pieces and then assembled by Motor Wheel; therefore, re-chroming of the wheels wouldn't be very practical.

There are NO SSII/III wheels with a 5" on 5 pattern.

[ Thanks to Jason Adcock for this information. ]


Aftermarket SSII / SSIII Wheels

Coker Tire has Olds SSII/III wheels in just about any size you like. How about that! Chrome or painted. Your choice. Something like 85.00 for painted, and 135.00 for chrome. Good deal if you ask me. The picture looks like it is of the "newer" style, with the short snap-on center cap, not the bolt-on, but not exactly sure. It may have been mentioned on the list before, but if not, now you know. Center cap not included.

The manufacturer of the Olds wheels from "Coker" is Specialty Wheel in Oregon, call them, the prices are probably better.

[ Thanks to Mark Cornea, Mike Rothe for this information. ]


Super Stock IV

This "polycast plastic, molded to a conventional steel rim" was available from the factory on 1971 and 1972 Delta 88's only. Price was $101.11 in 1971 and $98.00 in 1972. These were not aluminum. They appear to have raised ovals outside the lugs, and the rim itself is gray. 14x7 are option code PE1, 15x7 are PE2.

These are a steel wheel with a soft plastic facing moulded onto the wheel. Motor Wheel, which is a large OEM wheel manufacturer produced such wheels in the late 60s and through the 1970s, and other OEM manufacturers may have produced similar products as well. Motor Wheel also sold aftermarket wheels under their own name for a few years, including a polycast wheel called the "Exiter" which was similar in appearance.

If you can get close enough to a polycast wheel to touch it, they're easily identified because the plastic material is fairly soft. Soft enough, that the edges of oval openings can be deformed slightly with just a little pressure from a finger. The plastic rebounds right back into proper position as soon as the pressure is removed however, meaning that the wheels are fairly durable and therefore maintain their appearance well.

The down side is that under the fancy facing, they're steel wheels, so they're heavy. Heavier of course, than a plain steel wheel, due to a couple of pounds of plastic material having been moulded onto the wheel. At the time however, they were considerably cheaper than any aluminum wheels.

[ Thanks to for this information. ]


Cast Aluminum Sport Wheel

Option code N78 (possibly N76), Cast Aluminum Sport Wheel with Die-Cast Ornament. Available in 1978, $290 on the Salon and Supreme, $274 on the Supreme Brougham and $283 on the Calais. These are the same wheels that were part of the 1979 & 1980 W-30 packages, but they were only available in gold. Still available in 1981, the price changed to $292 for the Cutlass Sedan and Supreme, $284 on the Supreme Brougham and $273 on the Calais. They were gone for 1982.

[ Thanks to for this information. ]


Magnum 500

These are SSI's, but used by Ford and Chrysler. They were built at the Kelsey Hase plant in Michigan. The 500's came with either chrome or trim rings depending if they were 1969 to 1972. No trim ring. (??)

[ Thanks to for this information. ]


Full Size Wheels

There are NO SSII/III wheels with a 5" on 5 pattern.

The later (77-up) RWD Deltas used the 4 3/4 pattern unless equipped with a 403 in which case they had the big bolt pattern that the 98s and Custom Cruiser station wagons have.

I've seen some late '70's and 80's Delta's, 98's with the Olds SS wheels and a few with factory alloy wheels and chrome wheels. It seems that anything after '76 with a 350 or less, without the tow and/or handling package, would have the Cutlass 4 3/4" bolt pattern wheels. '77-'79 with a 403, and maybe the tow package during those years, gets the 5" bolt pattern. Those measurements are the diameter of the bolt pattern - that's from one bolt center, through the wheel center, to the other side, halfway between two bolts. Not the easiest to measure when the different is 1/8"! An easy check I've found is that the Cutlass 4 3/4" wheel measure 5" exactly from the outside of one bolt hole to the outside of a bolt hole on the other size of the wheel. The 5" full size ('65-'76, some '77-'79) measures about 1/4" more. One of the extensions in my toolbox is 5", so I use it as a go-nogo guage. Very fast when checking a rack of wheels! I've found checking on the wheel's back side is quicker.

Here is what I did on my '66 Dynamic 88 that I owned years ago. I took '71 to '76 full size pontiac ralley wheels (they also came on newer fullsize Pontiac wagons) painted the area around the 5 spokes black, bolt the SSI centers on them and use 15 inch Olds trim rings found on later Cutlass and Delta models. Man did I ever get the questions, "Where in the h*ll did you get large bolt pattern Super Stock wheels from???" I always had everyone guessing!! It looked really cool too!!

If needing a wider 5" bolt pattern, you can use the 15X8 rims from the mid 70s-80s GM 2wd pickups. Most are "sport" wheels, but hubcaps should still cover them. You can find plain 15X8 truck 5 bolt rims, but they are rare. Most of the plain truck rims are narrower than 8". I have one plain 15X8 rim if you can find another one.

For differentiating between Chevy and Olds SSII and SSIII wheels, try this. Facing the wheel, rotate the cutout to the bottom of the wheel. The chevy design cutout has verticle sides with a triangle top (sort of a triangle on top of a square). The Olds design has no verticle sides. It's more or less a strange looking triangle (triagnel with rounded corners). Check a chassis manual. H5> [ Thanks to John Pajak, Tony Waldner, Dave Brode for this information. ]


Full Size Factory Rocket Wheels

These were a new wheel for Olds in 1990, and it was the only year they were available from the factory. Olds factory alloy wheels, alloys with a series of "ribs" radiating out from the center at different heights (much like the wheels used on Buicks of the early 80's). These had centers with large Rocket logos on them. 1991 brought the new Caprice body along with a different wheel.

[ Thanks to for this information. ]
[ Thanks to Blaine Sanders, Paul Martin, Joe Padavano, Greg Beaulieu, Nick DiGiovanni, Kurt, Dan, Glenn, Mark Prince, Mike Fisher, Paul, Jason Labay, Tom Stoner, Bob Barry, Roger Heath, Bill Culp, 37th Hollander Interchange Manual, Duane, Jim Chermack, Kevin Wong, Duane for this information ]


1980's SS Wheels

All the H/O's and 442's in the 80's came with 15" wheels. They did make the same type wheel for the others in the 14" size, but it is not as 'rare'. The H/O or 442 wheel had a pinstripe around them and different color keying. The H/O used red pinstripe with silver/argent paint inlay, the 442 used gold/gold. The 14" wheels used, at least what I've seen, black paint inlay. Of course ALL Olds wheels are special IMHO, but I would say rough guess, if they aren't pitted, maybe about $75-100 each. That's only a rough guess.

Al H/O and 442 wheels were 15x7's. I think the 14" chrome wheels were an option for other Olds models. Definitely something special, but not extremely rare. If they're in decent shape, maybe $200-$250 for the set.

The H/O wheels look like they're all chrome from a few feet away, but if you look closely you'll notice that the centers (around the lug nuts) are painted argent. They also have a red stripe around the rim. 442 wheels have a gold stripe around the rim and gold paint where the argent is.

A chromed version of the Super Stock III wheels was offered from 1983-1988 and came in two sizes, 14 x 6 and 15 x 7. The 14" option code was N66 and N83 was the 15" option code. The N66 wheels were available on any RWD Cutlass from 1984-1988, except for the Hurst/Olds and 442. They had black painted insets and no pinstripe around the edge of the wheel. Center caps show a black background with the red rocket symbol in the middle. The N83 wheels came only with the high-performance Cutlasses (H/O, 442) from 1983-1987. The Hurst/Olds wheels had argent painted insets and a red pinstripe, whereas the 442 versions had gold painted insets and gold pinstripes. Also distinguishing the 442 wheels are the center caps, which read '442'. All wheels were of a two-piece design. They were chromed as separate pieces and then assembled by Motor Wheel; therefore, re-chroming of the wheels wouldn't be very practical.

[ Thanks to Tom Lentz for this information. ]


16" Wheels

Someone on this list asked if anyone had put 17" wheels on their 70-72 Cutlass. I didn't, but I DID put 16" wheels on my 72 Supreme, with 225/60/16 Falken H-rated tires on them. The new wheels and tires look great, they really transformed the look of my car from "elderly gents beater transportation" to "almost kinda beater hot-rod" and the car definitely grips better in the turns. I love the end result. But getting there turned out to be a long and painfully exasperating experience, despite the fact that I tried to be well informed when I started out.

Before I went looking for new wheels, I did a little reading to find out what info I needed. I measured the backspacing on my existing wheels (3 7/8"), measured how much clearance I had around the existing tire, and made sure I knew my bolt-circle (4.75"). I decided to keep the tire height the same during my upgrade (by going to 60-series tires from the original 75-series Michelins) to avoid throwing my speedometer calibration out of whack. I lucked out by finding an ad in a local paper for a set of Pontiac Trans-Am 16x8 factory alloy wheels for $150. I went to the guys house, used my home-made paper template to confirm the new wheels had a 4.75" bolt-circle, and measured the backspacing of one wheel, which was 4 1/4". This was 3/8" more than my stock wheels, but I knew from my measurements that this would be no problem, so I talked the guy down to $120 for all four wheels (best deal I've got in a long time!) and headed home.

First snag, I took a look at the new wheels and found that they needed a different type of lug-nuts, ones with a big flat shoulder that seats on the wheel rather than the usual conical face that steel wheels use. I hunted all over two cities and about 7 different auto parts stores and even a couple of wheel & tire stores without finding the 7/8 - 20 nuts I needed (everyone had metric nuts for Hondas and similar wrong-wheel drive econoboxes). Finally I gave up, found what I needed (hah!) in the Jegs catalog, and ordered them. Turns out that Jegs is about as far as possible in the US from where I live (Los Angles), so they told me it would take something like 10 working days for the parts to get to me; I groaned, but seeing no alternative, I agreed.

Okay, might as well get the tires. Hunt through all the ads, find a discount tire place that has what I want, call them, they don't have the size I want in stock, but can get them in a week. That's a week before the lug-nuts get here, so I go ahead. I spend one weekend cleaning, sanding, and re-finishing my wheels with Plasticote bumper-chrome (comes out looking pretty close to satin-finish aluminium), then I go get the tires mounted. While rolling the wheels and tires into my garage I suddenly notice that the backspacing on the wheel in my left hand looks different from the backspacing on the wheel in my right hand. Big sinking feeling, I measure and find I have two wheels with 4 1/4" backspacing, and two with 4 7/8" backspacing! What in the world! Do more research and find that yes, F-bodies actually came from the factory with different backspacing on the front and rear wheels. Believe it or not. So now I have two wheels with 1" more backspacing than my stockers, and I'm no longer so sure they'll fit my car. And I just bought new tires and mounted them, too.....

I wait till the lug-nuts arrive, try them on, and find that the shank of these new nuts is just a little too thick to go into the holes in my wheels. $%&&8##, this is starting to get nasty. What the heck, I'm in up to my neck, I might as well go for broke. I take my tires and wheels in to work, one each day, and use our Brideport milling machine with a 11/16" drill chucked up in it to drill out all 20 holes in my 4 wheels. Okay, time to put the wheels on. I put the thick washer on the lug-nut, slip one into the newly opened up hole in a wheel. Then I find that the lug nut shanks are also about 1mm too long - the nuts bottom out on the wheel-stud by hitting the brake rotor/drum without actually clamping the wheel down at all!

Okay, this one should be easy, I'll run down to the store and buy some more hardened washers the same size as the ones that came with my lug-nuts, I'll just stack two washers on each nut, simple. I get my new 5/8" hardened washers home, then find that their outer diameter is just a teensy weensy bit bigger than the washers that came with the new lug-nuts. You guessed it, they are just big enough not to enter the recessed holes in the alloy wheel that lead to the actual seat for the lug-nuts!

By this time nothing surprises me any more. I decide to buy smaller washers and drill out their centres. I go back to the hardware store and buy 9/16" hardened washers; these are small enough to go where they should, but the centre hole is too small to slip over the lug-nut shank, so I take them in to work. After a few false starts I make a simple jig to hold one washer at a time in the good ol' Bridgeport, and get the centre holes all drilled out to 11/16"; the drill bit wears out halfway through (those hardened washers really were hardened!), so I re-grind it on the grinding wheel, and finally get about 25 washers drilled out (a few spares just in case).

I think about the wheels backspacing situation for a while, there's more clearance on the inboard side of the front tires than the back, and the 8" wide deep-backspacing 4 7/8" wheels actually place the centreline of the tire in the same place as the old 6" wheel with 3 7/8" backspacing, which is good for maintaing the steering scrub radius, if only they will actually fit on the car and not hit anything, so I decide to put the deep-backspacing wheels on the front and the other ones on the back.

Yes, the story ends happily, this finally did it. I used one of my drilled-out washers and one of the Jegs-supplied washers on each lug-nut, and all the wheels went on okay. There is a very reasonable amount of inboard clearance( maybe 1" - 3/4" for the back wheels (225/60/16 tires on 8" wide rims with 4 1/4" backspacing), and lots of clearance on the outboard side of the tires. At the front, with the same size tires on the same 8" wide rims with 4 7/8" backspacing the inboard clearance is tight, the tire sidewall gets to within maybe 3/8" of the brake-hoses, but nothing hits. Once again there's lots of room on the outside for more tire width.

Guess I'll never believe in "easy bolt-on's" again! It took me about three weeks and much aggravation to get those wheels and tires on.

[ Thanks to John Carri for this information. ]


Wire Wheel Covers

I myself just picked up a set of used wires for my 85 Toro last week to replace the non-original caps that i bought the car with. I went for the "dismantle" they were filthy !. It's not that difficult, there will probably be some 7mm bolts on the backside of the center cap. Once you remove that you just need to pop the spokes out. DO ONLY 1 WHEEL COVER AT A TIME , DO NOT DISMANTLE ALL 4 AT ONCE !. It might seem that it's a no brainer putting the spokes back in, but believe me from experience and a lot of 4-letter words, there is a certain "pattern" to it. So do one at a time and as you put the one back together, have one of still dirty ones to use as a guide. If you don't put the spokes back in properly, the spokes wont lay flat enough to the center of the wheel cover and you will never be able to push the center cap down tight/close enough to thread the 7mm bolts back in from behind.

If you choose not to dismantle, wheel acid cleaners work but are risky. If you do choose to use them spray on, let sit a few and rinse, don't scrub the cleaner into the wheel. Rinse first then scrub with plain soap and water for stubborn, preferably with a sponge, not a hard bristle brush you would use for tires, or interior cleaning. The finishes on these wire wheel's that will really show age and wear is the chrome plated center sections(the center cap, and the piece directly underneath it). These are the most delicate parts that if scrubbed too hard, or you use the wrong chemicals, and or too much of a chemical on, will look like crap. You will start to dull the finish, because this can actually start removing the chrome from the metal. The rest/remaining part of the wheelcover generally holds up better to age and wear.

Since mine were so grimy, the first thing i did was go over ever thing very lightly/gently with steel wool. Watch that flat black painted area close to the edge of the wheelcover, you don't wan't to be steel wooling that at all. I then went over all of it (except the flat black) with Blue Magic Metal Cleaner.

[ Thanks to for this information. ]


Restoring


Colors

This is the breakdown on all the colors for SS wheels:
SSI's all years inserts flat black
68 14x6 SSII Wheel is Argent with silver around the 5 holes (no trim pieces)
69 14x6 SSII Same as above but with trim on the 5 holes and no silver paint edges.
70 14x7 SSII Pace Car and Rally 350 were the only ones body color this year, all others were Argent gray.
71-73 14x7 SSII All were Argent gray like 70's.
71-73 14x7 SSIII Were the same wheels as SSII with the lower body color of the car on the wheels.
74 SSIII 15x7 (bolt on cap, one year only) Lower body color.
75-77 SSIII 15x7 (snap on cap) Lower body color.

The shade of silver, cast grey or cast iron, is technically called "Argent", and several vendors sell it in spray cans. Unfortunately, all seem to be a slightly different color.

[ Thanks to Jim Chermack, Joe Padavano for this information. ]


Painting

I thought I saw a "with precut masking kit" that either Year One or Eastwood, or some darn place had. Mask, scuff and paint. Fairly straightforward. Maybe it was for the Chevelle wheel, which was similar. Don't remember. I haven't had a set of SSI's in quite some time. I do remember the black wasn't real shiny, something of a dull, very low gloss black. Either way, you need to start with a super clean surface, and all existing paint nicks, chips are at the very least feathered out and smooth. A good cleaning with some precleaner and a Scotchbrite pad only in the blackened areas should do it. DON'T scrub the chrome. If you are real handy with an X-Acto knife (razor knife) you can use regular masking tape and trim the overhang to where you need it. Any good chrome polish should work for the chrome sections of the wheel. Any inadvertant overspray onto the chrome parts can be removed with some paint thinner on a Q-tip, followed up with the chrome polish. I've used this on chrome SSII wheels in the past.

I just did a set, I stripped them to bare metal with a spray on stripper. I sandblasted one but the stripper is more effective for maintaining a smooth surface. The sandblasted wheel took more sanding for a smooth finish. I then sprayed a good rust inhibitive primer (3 coats with sanding in between with 400 grit wet-dry). Lastly I sprayed the wheels with Dupli-color to match my car. Two cans will put two good coats on 4 15" wheels (outside only). By the way, the stainless inserts remove and reinstall easily, don't try to mask them.

A perfect match in a standard spray can for the gold on your 442 wheels is GM-294 (Dupli-Color) Camel Metallic. It comes in the standard small spray can.


Chroming

Many of the shops that modify stock wheels can also rechrome them. Try Stockton Wheel, for example. Repainting the black areas is the problem, as getting the paint to stick to the chrome can be a challenge. I've heard (though not yet tried it) that the newer self-etching primers exhibit excellent adhesion to chrome. You might want to ask the question at the painting bulletin board.

The red stripe does have a GM part #, it might still be available. Otherwise, two methods would be to have a pinstripe painted on, or to go to your local auto parts store and buy some vinyl sticky back pinstripe. If done carefully it could come out nice. Or look in the aftermarket for a repo stripe.

As far as my situation, one full set (4) was purchased from one source with one rim severely bent, one pretty rusty, the other two in fair condition but still in need of help. The other two I bought just incase the one bent rim could not be fixed. This pair also included a bent rim, but not to bad and both looked like thye were brand new, other than the damage. So I would have to mix and match a set out of the six. I would be worried that they might not look like a matched set if I didn't repair and rechrome them at the same time.

So I figure, that with my purchase price of less that $200 for all six, and the cost of the repairs, I should come close to what an NOS set would cost, if they are even still available. And even NOS are not guaranteed to be without some light surface rust and shelf wear. So I think I'll just about come up even if I go the full reconditioning route.

[ Thanks to Joe Padavano, Bill Reilly for this information. ]
[ Thanks to for this information. ]


Widening / Adapting / Interchange


Widening

Weld Craft (313-420-2211) in Plymouth, Michigan widens rims and fixes aluminum rims. Always add the space to the front.

I had my rims widened by a local sprint/dirt track race shop. They took the 15" x 8" rims, split them on a lathe and then welded a 2" band in to make the wheels 15" x 10". The job was very well done and the welds were done with a Tig welder, so they even hold air. The rims now have 50 series tires, and the split was done on the front face of the rims, so the back spacing didn't change. This way the wide tires won't rub on the inner wheel wells.

There may be a problem finding a shop to do this since there are major liability concerns with this type of work, but if you have any type of racing near your area, you should be able to find a shop to perform the work.

[ Thanks to Don Gatrell for this information. ]


Wheel Spacers

Using wheel spacers will put some bending stresses on your wheel studs, and they're not designed for bending stresses, just for axial (stretching) forces. Go too far with thick spacers, and you risk breaking wheel studs, probably at the worst possible time such as during a burnout or hard cornering. The rule of thumb I've read is, don't ever use a spacer thicker than a quarter of an inch. Even with that thin a spacer, make sure the studs are long enough to adequately engage the lug nuts.

Depending on how long the central hub on your rear axle/front brake rotors are, even a quarter inch thick spacer might move the wheels out far enough to no longer be hubcentric - they may no longer be positioned by the centre hub, but rather by the lug nuts only. Many aftermarket wheels are lugcentric (lug nuts centre the wheel) but I know of no OEM wheels that are - for good reason. Hubcentric is a better design.

On my '72 Supreme I tried out quarter-inch thick wheel spacers on the front spindles to see if they helped some wheel clearance problems I had. Used on the big 12" 1LE brake rotors I have, the wheels were still hubcentric because the big rotor has a long central hub. On the other hand the 11" stock '72 Supreme rotor had a much shorter hub and the wheel would probably no longer be hubcentric with a 1/4" spacer.

I looked around the local auto parts stores and found a zillion 4-hole spacers designed for Hondas, but *none* to fit my car; cost was between 25 and 35 bucks per spacer, if I remember right. Since that seemed rather pricy, the spacers looked like cheapo porous castings which didn't look very strong, and there were no 5-hole ones to be found anyway, I made my own. I pulled off a rear brake drum from my car, and used that as a template to lay out the position of the holes on a piece of 1/4" aluminum sheet, then cut the whole thing out on the milling machine at work. You could probably do the same with just a big drill press and a narrow bladed saw, like a fretsaw.

One more thing about wheel spacers, they make a handy template for finding good used wheels or brake drums or rotors at the junkyard! They're easiest way to tell the 5x5 from the 5x4.75 bolt patterns.

[ Thanks to John Carri for this information. ]


Wheel Adaptors

I tried a pair of these on a 55 ch*vy many years ago and did not like them. They creaked and groaned every time I turned the wheel. They move the center line of the wheel out, which has the same effect as too much offset. The load on those little plates is tremendous and I did not trust them to hold up very long. Dad had a set on a dune buggy with no problems, but it was a whole bunch lighter than the 55. Your truck is no light weight either. I would suggest having the drums and axles drilled to accept the 5 bolt pattern. It might cost a little more, but it will be safe.

[ Thanks to Dave Wyatt for this information. ]


Interchange

See Interchange for information.

[ Thanks to for this information. ]


Tires


Tire & Wheel Size Considerations

Measure, Measure, Measure
I'd like to say first that the only way to be *sure* what will fit your car is to crawl under it with a tape measure and measure all the clearances. Take off a stock wheel (or use the spare) and find out what backspacing you have now. Measure how much clearance you have on the inboard and outboard sides of each tire, on both sides of the car. Turn the front wheels all the way from lock to lock, and measure how much clearance you have between the tire and all the things it gets close to (fender, frame, brake-lines, sway-bar, fender-liner, etc,etc) at both ends of steering travel as well as in the middle. Measure boths sides of your car, it is very common to find that the body has shifted on the frame or been in a minor fender-bender that caused the two sides to have different clearances. You'll get dirty, but you'll then know what fits your car, since you can figure out how much change in backspacing you can accept, and knowing the sizes of your old tires and new tires, you can calculate how much of the available room you will use up.

My car is a '72 Supreme 2-door, which may have different sized wheelwells than your '69 'vert - I don't know. The stock steel rims on my car had 3 7/8" backspacing. The 16x8 rear wheels I have now have 4 1/4" backspacing, and they have more clearance on the outboard side than the inboard side, with 225/60/16 tires. The front wheels on my car are also 16x8", with 4 7/8" backspacing, different from the rear wheels. That happened by accident, but it turned out to be a good thing, as the tires (same size as the rears, 225/60/16) barely clears everything, even at full lock. With the Hotchkis lowering springs, my tires tuck up inside the front wheelwells, and in high-g cornering the lousy front suspension geometry of our cars causes the top of the tire to roll outward just far enough to ocassionaly touch the plastic inner fender lining.

The tires you're planning to use (245/50/16) are 25.7" tall, while the 225/60/16's I'm using are 26.6" tall, almost an inch taller. So your car will end up half-an-inch lower than mine, all else being equal. I have to use the small hydraulic jack under my car now, because the big one won't fit under the front frame cross-member.....so I'd suggest a check on your ground-clearance too. (I'm using the Hotckis springs which lower the car about an inch so you may not have this problem.)

As you say, there is lots of room for bigger tires both front and back. I was trying to do this on a limited budget, which meant I was stuck with factory wheels, and I ended up with 16x8 Firebird wheels. Two or three books on handling that I have state that for a given tire size, one should use the widest rim that will fit that tire for the best handling and feel (wider wheels "brace" the tire sidewalls apart and make the tire stiffer against sideways forces). That is to say, for a given rim width, one should use the narrowest tire that will fit on that rim for best grip. I realise that this goes against the popular belief, but I have it from a couple of authoritative sources. The narrowest tire that would fit on an 8" rim was a 225, which is what I used.

Using this criteria, to fit those 315's you'd need something like 11" wide rims. With only 4" of backspace those wheels would stick out a long way. Not sure how well they'd fit.

One more thing, the two ball-joints in the front suspension dictate the line about which the front tires pivot (steering axis) and this hits the ground somewhere in the tire contact patch; the distance from this point to the centre of the tire contact patch is called the scrub radius, and if it is changed too much steering feel, loads on the wheel bearings, tie-rods, etc, all change for the worse. Using extremely wide tires and stock offsets will increase this scrub radius considerably.

He might have them up front but that's WAY to much rolling resistance and contact patch for the delicate suspension components to muster over long time especially if you have rubber bushings. you will accelerate wear as well as harm the tire ah he alreadr states the rub factor that stresses the components and heats/damages the tire. Trust me ray. 235/60/15" on 7" with stock offset on front, 255/60/15" with 8" and stock ofset on rear. You'll not rub and tire contact will be more than sufficent. Not to mention the extra initial bucks there larger tires and spacers cost and the occasional tire boo boo because of rub. I spent quite a while researching tire/wheelsize/wheelwell clearence with suspension flex both with rubber and Polly bushings. Your safest/best fit/longest lived combo I've told you. Unless your use is the track only than stuff those rear puppies with slicks. But for overall street use. You might envy the wider meat these other have but you won't suffer the accellerated replacement costs or higher initial purchase cost. Your tires/car/and pocket will thank you. BTW, I spent 5 years in the tire field. Both recapping and retail. Sure the customer is always right. Especially when they are right brings them back early for new, smaller tires. Do it right the first time. You'll thank me and have a couple bucks to spaire to rebuild that carb or do an allignment (suggested) right off the bat.

I think part of the reason there is so much disagreement on this issue is that all of us have different opinions on what tire is desirable. It's absolutely true that tires with big aspect ratios (like 80 series and 75 series tires) have tall sidewalls that are soft enough to bend over and accomodate a relatively narrow rim. The cross-section of these tires looks relatively close to an O shape. Because the sidewalls are tall and curve over, the tread is able to lie flat on the ground as intended, and the tire doesn't wear unevenly, as Blair said. Because all tires were built this way twenty five years ago, the manufacturers put narrow rims and big tires with tall sidewalls on the cars back then.

However: an 80-series or 75-series tire with tall sidewalls, curved in by mounting them on a narrow rim, also gives you just about the crummiest possible transient handling response. When you steer the car into a turn, the tall tire sidewalls deform sideways more than you can believe till you actually see it - look for photos of handling tests on some 70's era American car in old copies of car magazines - the tread can move some three or four inches sideways relative to the beads on the wheel! So when you turn the steering wheel, first the tires deform, then they "reach the end of their rope", then the car slowly and reluctantly starts to change direction.

I hate this kind of handling, so I would never use 80 or 75 series tires on any of my cars, and it never occurred to me that anyone else would voluntarily do so, either!

When you use tires with a lower aspect ratio like a 60 series or 50 series tire, the sidewalls start to get shorter and stiffer, and the cross-section of the tire starts looking more like a square-bottomed U than like an O. This kind of tire works best on a rim that is about as wide as the tread itself, or alternatively, the tire section width is about 10 - 15% wider than the wheel. If you squeeze these tires on a narrow rim, the sidewalls won't curve, instead the tread itself will, and you'll start to get higher wear in the centre of the tread.

Perhaps I can put an end this thread by suggesting this: If your goal is to put the widest possible tires on your wheels, you're better off using a 75 or 80 series tire. The result will be the big-tire look, combined with, shall we say, vintage era handling. If on the other hand your goal is to get better handling as well as the big-tire look from your car, choose 60 series or lower profile tires, pick the widest rims you can afford or fit on your car, then pick tires no more than 15% wider than those wheels. The car will respond much more quickly to what you ask it to do via the steering wheel. Do this with no other suspension mods and your Olds will roll violently as the tires quickly respond to your steering commands; but add stiffer anti-roll ("sway") bars, and/or springs and shocks, and the car will become far more nimble than it used to be, and far more fun to drive. Roger and I can testify to that! ;)

[ Thanks to John Carri, Gary Couse for this information. ]

Affects on Differential Gear Ratio
Jeff Newman wrote: But here's where my thinking gets me to. Swapping tires is a whole bunch easier than swapping a rearend or ring and pinion, so why doesn't anybody change them instead? Stefan Gadecki wrote: So, theoretically if you spin the larger diameter wheel at the same rate as the smaller diameter wheel, you should cover the distance faster correct? Am I missing something? Yep, in order to spin the larger diameter tire at the same speed as the smaller one you would need a proportionally greater amount of torque and power. Big diameter tires have some obvious drawbacks such as: 1) generally they will be heavier. The tire is part of your rotated mass and part of the unsprung weight so heavier is bad. 2) they have more inertia because the rotating mass is further from the center of the tire. In order to move the car forward it must first rotate the tire (duh). In order to rotate the tire it must overcome the tires inertia. Ergo, more inertia is bad. 3) they require more room in the wheel well which may mean having to "jack" the car up. Very bad for weight transfer. So why don't racers use smaller diameter tires? I believe larger diameter tires have two benefits. 1) they have a larger contact patch. For the same width, air pressure, tire construction, and material a larger tire will have more rubber on the ground because the patch is longer from front to back. This is a good thing. 2) they apply the force more parallel to the ground. The force is applied at a tangent to the surface of the wheel. With any wheel you can draw a line from the center of the axle directly down into the ground. This line is perpendicular to the ground and the turning of the tire moves the tire under this line from front to back. The force being applied through the tire under this line is parallel to the ground and 100% of it goes to moving your car forward. Only a fraction (from 99.9% to 0%) of the force applied through any other line goes to moving your car forward. With a larger tire more of the force will be available to move the car forward. That's my poor understanding. Of course tire size is a balancing act. Over a certain size the weight and inertia disadvantages out weight the advantages. Probably the smallest diameter tire that you can get to not spin is the best. You note I keep saying diameter to avoid the confusion of greater width. The contact patch is directly proportional to the width.

[ Thanks to Cliff Simpson for this information. ]
Sidewall Ripple
I think ripple is an effect rather than a cause. That is to say, I don't think it's a really good or bad thing just a result of tire construction. If you could get the same size tire of the same sticky rubber to have the same contact patch I would expect it to perform similarly. It just that the tire construction "requires" wrinkles to get the larger contact patch. I think.

Did you know that rubber expands and compresses very little? It deforms which is different.

Ripple tires actually give you a "cushion" when launching. The axle (rim) has "room" to move before the outside of the tire (tread) does. Resulting in the car squating for a longer period of time during launch, therefore giving you better weight transfer to the rear. The downforce keeps your tires planted, otherwise the rear suspension will unload and your tires go up in smoke. You have to factor in spring weight (stiffness), shocks, type of rear suspension (4-link, ladder bar, stock) into the equation also.

[ Thanks to Cliff Simpson, Randy Geisel for this information. ]

Technical Stuff

For maximum lateral grip in the twisties, and best turn-in feel, the rule of thumb is this : Use the widest rim recommended by the tire manufacturer for that tire.

In the absence of information from the manufacturer, you can get close to the ideal rim width as follows:
Divide the tire section width by 25.4, which will convert it to inches. In your case, your tire is nominally 255/25.4 = 10.04 inches wide at the widest point. For maximal lateral acceleration out of your car, pick a wheel rim within about +5% to -10% of this width, i.e, for a 10" tire a rim width between 9" and 10.5" wide.

While this tells you what rim width is best for a 255 tire, it does not tell you if that tire and wheel will fit in your car! Many people run 255 tires on 8" wide rims, and I believe some people on this list have fitted this combination on their G-bodies. However an 8" rim is not wide enough to properly support a 255 tire. The sidewalls will be bowed in to meet the narrow rim, which makes the tire weak against lateral forces (cornering forces). Here's the catch, though. If you use the appropriate 10" rim, the tire/wheel combo gets wider than the SAME tire on an 8" rim. Think of the sidewalls as "hinged" where they are attached to the edges of the tread, the free ends are spaced apart by the rim. For every 1" wider the rim gets, the midpoint of the sidewall moves roughly 1/2" outwards! So a 255 tire on a 10" rim is going to be about 1" wider at its widest point than the same 255 tire on an 8" rim. I don't know if this will fit your car or not.

If you need to go smaller to fit the wheel-well, a 235 tire on a 9" rim or a 225 tire on an 8" rim (this is my combination) will likely give you more grip and better transient response (turn-in) on the twisties than a 255 tire on an 8" rim.

My information comes mainly from Fred Puhn's book How to make your car handle. You can also take a look at OEM tire sizes for newer high-performance cars and usually you will find that the tire is about the same width as the rim. This gets more and more important as the section height of the tire gets smaller - the sidewalls on a 35-series tire are so short and stiff that there is very little choice of rim widths - pretty much only the rim exactly as wide as the tire will fit. On the old 80-series tires one could get away with pretty narrow rims - lousy for cornering, but a help for straight-line acceleration.

Not always same size all around, but you're right about a specific ratio of front to rear tire sizes for best handling. The main ingredient behind this is as follows. Lets say there is 200 lbs of weight on a certain tire. Our hypothetical tire has pretty good grip and you can now push it sideways with 180 lbs of force before it loses grip and starts to slide. That means that the tire has 180/200 = 0.9 G of grip.

Now if you put 400 lbs of weight on the same tire, it shouldn't slip till you push sideways with .9 x 400 = 360 lbs of force, right? Actually, no. It might support, say, 320 lbs of side force before sliding. Its grip went DOWN, from 0.9 G to 0.8 G, as the weight on the tire went up. This is how ALL tires behave. This is why lighter cars corner better than heavier cars.

Now, the four tires combined support the entire weight of the vehicle; we just saw that putting more weight on one tire LOWERS its grip. So, to get the most lateral grip, the car should have equal weight on the front and rear tires, or a 50/50 weight distribution. With equal sized tires at all four corners, this car could coast through turns faster than any other combination of tire sizes and weight distribution. In real life one doesn't coast through turns, the engine is feeding power to the rear tires (RWD car), so they need more grip than the fronts in order to handle the additional forces from the engine as well as the cornering forces. So the car should have 50/50 weight distribution and rear tires somewhat wider than fronts. This is exactly what a Dodge Viper has....

What if your car is nose-heavy, as all our Oldsmobiles are? Well, weird though it sounds, such a car could coast through turns fastest if it had wider FRONT tires than rear tires. In order to apply power through turns instead of coast, the rears get somewhat wider. How much wider? It depends on the weight distribution, and cornering style of the driver, but equal sized tires all around or slightly bigger tires in FRONT would probably corner best!

Note that cornering balance - understeer/oversteer - is also affected by tire sizes. Wider tires on the rear contribute to understeer, wider tires on the front to oversteer. For any specific set of tires, the swaybars and springs can be used to help tune the handling balance. But here's a little realised fact - swaybars and springs can only WEAKEN the grip at one end of the car, not strengthen it (one exception, see below). They affect handling balance by shifting more weight to the outside tire that has the stiffer springs or swaybar, weakening its grip. If your car understeers, that means the rear has more grip than the front, and a stiffer rear swaybar will weaken the grip of the rear tires to match your fronts. Now the car will corner more neutrally. But you would have neutral handling and MORE overall grip if you instead put on bigger front tires (rather than the stiffer rear swaybar).

Exception: If poor suspension geometry is reducing the grip at one end by tipping the tires on their sides as the body rolls, the swaybar reduces the amount of roll and lets the tires stay flatter. The flatter tire position increases grip, the extra weight transfer from the stiffer swaybar decreases grip. The net outcome - grip increased or decreased - depends on just how bad the suspension geometry was and how stiff the swaybar was.

Backspacing is basically this : how deep a "bowl" does the tire/wheel combo form on the inside face. To measure it, lay the wheel face-down, lay a straight edge across a diameter, and measure the depth to the mounting surface.

As you can see, a larger backspacing will move the tires in towards the cars centreline. When you use fatter than OEM tires, you may have to choose your backspacing carefully to position the tire in the wheelwell so that they dont rub on anything.

A related term is wheel offset. This is a measure of how the wheel's backspacing differs from its "frontspacing" (not a real term, but it helps get the idea across). An 8" rim with 4" backspacing has no offset (mounting surface is 4" from both inside and outside edges of rim). An 8" rim with, say, 5" backspacing has one inch of offset towards the outside of the wheel. (5" from inside rim to mounting surface, 4" from inside rim to wheel centreline, hence 1" offset to the outside).

Why mention offset at all when its obviously more confusing than backspacing? The reason is that when engineers design the front suspension of a car, they design the centreline of the tire to be in a specific place with respect to the steering axis (line through upper and lower balljoints. If the steering axis goes through the exact centre of the tires contact patch, steering is easiest, and the tire can turn easily without "scrubbing" across the ground. In practice the steering axis is usually designed to meet the contact patch a bit inboard of this position. This small amount of "scrub radius" improves steering feel. When you put wider tires/wheels on the car, you can maintain the same scrub radius if you use wheels with the same OFFSET as the stock wheels, not the same backspacing. This lets your car steer as designed, and will probably reduce wear and tear on your ball-joints, bushings, tie-rods, and other bits and pieces. Also if the engineers did a good job of centering the OEM wheel in the wheel-well, your new tires and wheels will also be centred.

My stock rims were 5" wide, with 3 1/2" backspacing. That means they have 1" offset to the outside. (3 1/2 inch backspacing, 2 1/2" from inside rim to centreline of wheel, hence 1" offset to the outside. If I want to replace these rims with 8" rims and keep the same scrub radius, I need the same 1" offset to the outside. So I need an 8" wheel with 5" backspacing. (5" backspacing, 4" to the centreline, hence 1" offset to the outside).

Of course, a big fat tire on an 8" rim with 5" backspacing may end up not fitting your car. When you try to fit the biggest possible tires on your car you usually sacrifice scrub radius, suspension wear, and maybe turning radius in exchange for looks and better traction. You have to decide which trade-offs you want, but now you have the information to make an informed decision.

I've tried hard to make this offset thingy understandable rather than quoting the usual formula for calculating offset given rim width and backspacing. Hope this makes sense to someone out there...

Since the tire/wheel thread produced many responses, I went home and dug up more advice regarding selecting wheels and tires. Here's a quote from Hot Rod, April 1996 issue:

"According to David Shelton of Dunlop's proving grounds, Dunlop and most tire manufacturers recommend a wheel width between 70 to 90 percent of the tires section width. So if a tire has a 10-inch section width the rule of thumb is that a 7-inch wide wheel will produce a smoother ride but will be less responsive to steering input. Conversely, this same 10-inch-section-width tire mounted on a 9-inch-wide wheel will offer improved response and handling at the sacrifice of some smoothness."

This rule-of-thumb is fairly conservative, Joe Padavano posted BF Goodrich data for one of their 255 tires (10" wide) which stated that up to a 10" wide wheel could be used with it, while the 70% - 90% rule above says that the widest useable rim is only a 9-inch one. Here's another quote, this time from Don Alexander's book Performance Handling, subtitled "how to make your car handle techniques for the 1990's", published by Motorbooks International :

"The diameter of the wheel has no direct effect on traction, but it can change the tire contact patch area size if a lower aspect ratio tire is used on a larger diameter rim, with the overall tire rolling radius remaining constant. This wil also affect ride and responsiveness.

The width of a wheel, however, can have a major effect on traction. If the rim is too wide for a given tire, the bead will not seat properly. This can also happen if the wheel is too narrow. All tire manufacturers specify a range of rim widths for every tire. It is crucial to stay within this range for safety reasons.

But what effect does the width of the rim have on the tire contact patch? The rim width will affect the contour of the tire tread, and therefore affect the shape of the tire contacth patch. If the rim is too narrow, the tire tread will bow out and less than the maximum tire contact patch area will meet the road surface. It is unlikely to have a rim too wide within the specified range of rim widths for a given tire size.

After considerable testing, we have found that it is best on most tires to use the widest rim width recommended by the manufacturer for a specific tire. This will optimize the tire contact patch area for that tire, and allow the highest cornering force for that tire. Narrower rims tend to crown the tire too much, hence reducing the contact patch area.

Lets look at the problem from the other side. If you are limited to a maximum rim width because of rules, budget and other factors,then it is usually best to use the smallest-width tire that will fit on the rim. In most, but not all,cases, the smaller tire wil have a larger tire contact patch area. This will increase cornering force, improve tread wear and allow better suspension settings for overall performance.

We have found that most brands of tires respond in this fashion. However, some tires, due mostly to stiffer sidewall construction,are less sensitive to rim width differences within the manufacturer's specified range (of rim widths). "

Here's my attempt to distill all the information presented so far:

  1. Never exceed the widest wheel rim-width specified by the tire manufacturer. This will usually be between 90% and 100% of the tires section width.
  2. As long as rule (1) is obeyed, the wider the rim, the better the cornering grip. Smoothness of ride may decrease as the rim gets wider, though.
  3. If you already have a specific wheel, mount the narrowest tire that will fit that rim if you want the most cornering grip.

I guess the -10%, +5% (of tire section width) rule I posted earlier should be modified to -10%,+0% , with a check with the manufacturers data to make sure that the maximum allowable rim width hasn't been exceeded.

[ Thanks to John Carri for this information. ]

Examples

The tire sizes that are optimal for you car will depend on what will fit in your car, weight, weight distribution, spring rates, shock stiffness, and the size of your sway bars not to mention what kind of feel you prefer. With all that said, I would personally move up to the 15" rims, and if they are stock width and backspacing, you will be able to move up to 245/60's on the front and 275/50's in the rear. With an 8" rim in the rear (or wider, with factory backspacing) you can put 295/50's in the rear which will give you 10" of rear tread width. I ran this on my 72 and it handled very well, but I didn't have the same suspension setup.

With the 245/ 275's your not talking a major difference in width so your handling balance should stay the same and if anything give you more understeer. The major outcome will be more grip, both in the corners and off the line. The major problem I see about pushing the car in corners while upshifting/downshifting is that if you downshift and give it too much throttle, you may break the rear tires loose (easier to do than you might imagine with a big motor), but the larger rear tires will do two things. First off they will give the car more understeer at the cornering limit and also make it harder for the rear tires to break loose. Both of these facts will give you more of a safety margin if you should feel the need to push the car hard, but will be invisible until you do.

Yes you can fit larger than 295's on a 72, but I put them on 15x7 stock rims. You're not supposed to, but it worked, it just wore out the middle of the tire quicker than the outside. With a 8" rim I would keep the same backspacing as the stock rims which would give you 1" more towards the outside of the car. My car still had plenty of room on the outside, but the inside was as close as you'd want to go, especially if you have rubber bushings w/o a rear sway bar. The reason is that when you corner the rearend will shift some which will lead to minor rubbing. The sway bar and poly bushings will keep the rearend better centered and allow you to add 1/2" of backspacing but there is plenty of room to just go to the outside. If you look on my page, you can see the pics of my 72 which had the 295's on it. There are no real clear shots under the car but you can see how much clearance I had to the outside.

[ Thanks to Mike Bloomer for this information. ]



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