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Yes you read right! I have a 72 cutlass supreme with an ls engine 6 speed t56 full UMI suspension set up for protouring. I have raced the car a hand full of times now at willow spring raceway and its AWSOME!!!! I had issues in the beginning of course. Power steering pump, suspension set up, rear sway bar. But I was able to really dial the car in and had a great time. She not a show car by any means ( plenty of dents and rust with all red primer) but I still get complements at the track.
Ok so to the point, the car seems plenty fast with about 470hp to the wheels but the brakes need to be upgraded. Mind you I have 2002 Camaro calipers front and rear with drilled and slotted rotors. I came up on a set of CTS V brakes 6 piston calipers and 4 piston rears. So I made it work with my set up. Had to open up the center bore of the rotors to slip over the hub. An had to drill out the mounting hole for the calipers to 9/16. Front calipers and rotors now fit. So to my problem. My current wheel is the ridler 650 18x9.5 0 offset which should be 5.25 backpacking. I was under the impression they would work.😣😣😣😣 but the wheel contacts the caliper. Just barely! But I dont want to grind down the caliper to make it work. Plus I would have maybe a 1/8 of clearance. I dont like that idea.
So bigger wheels it is! I would like a 19in wheel but who even makes one???? I see alot of 20in wheels was planning on just going to the same ridler 650 in a 20x10 and I would like the same wheel on all four corners for front grip and ease of tire rotation.
Any other track guys or gals running large wheels??? What size and backspacing? Again I currently have a 18x9.5 with 275/40-18 square. I'm thinking 20x10 with 275/35-20 or a 295/35-20 if I wanted to go wider. I'm asking for anyone's help or input. Thanks in advance, oh and I am literally waiting on responses before I make a purchase for new wheels and tires but no rush.
I don't think you will be able to fit 20x10 in the front, I think widest wheel that will fit is 9.5" but that's in 18" diameter, I'm not sure about 20". As you go bigger in size the wheels is obviously taller and tires get more square, so what fits with 18" wheel might not with fit with 20".
You are really gonna have to measure, buy one of those measuring tools or go down to the tire shop.
Asking internet will result in your hard money spent on wheels that don't fit, cause when you are trying to maximize the tire/wheel size everything matters and there is no way to tell without measuring.
There is plenty of room in the rear if you wanna run staggered wheels, you could go 10" easily maybe even 11" wide. Most common combo is 20x10 - 20x8 or 20x8.5.
For the track the additional weight of a 20 vs a 19 or an 18 is bad enough but also the more you go in diameter the less you can go in width.
For the fronts if you do a 275/35/20 that tire is 27.6". That's way too tall for our 70-72 Cutlass/442s unless you go really skinny. Keep in mind there are guys auto crossing with 68-72 GM A-bodies with 18x11s and 315/30/18s on the front (with lots of mods) but that tire is only 25.5" tall. The taller you go the more room you need to both the inside and outside not to hit something. You've got the sway bar and frame to the inside and inner fender wells and fender to the outside.
Here's where you need some space - right at the sway bar and frame. HPljRzo.jpg
This is a 26.7" tire =245/45/18. Looking at this pic you can see if the diameter is LESS - lets say a 26" tire, you would have a bigger space here. But with your 27.6" 275/35/20 you wouldn't be able to turn the wheel more then about 75% lock to lock and that's just to the inside.
Here are some 305/30/19s = 26.3" tall - these will needs lots of mods to fit but can be done since they are shorter. BS has to be perfect to the inside which I believe a 6" BS on an 18x11 wheel is the sweet spot. But you will never be able to run a stock sway bar. It will have to be splined or custom made to give you about an extra 3/4" turn in then tons of mods, cutting, flat head screws etc to the outside. I have fiberglass fenders so less of a project for me but make no mistake it will be a big custom project. nTJEG56.jpg ShnGRBZ.jpg b9Qzl6S.jpg
The rear has it's own set of issues but the 20s will be much more forgiving there. You could run 20x10 or 20x11 with a 295 or 305 tire with no issues again with the perfect back space. Of course you could go big money here too and notch the frame and do a mini tub and go all the way to something like a 345 tire but that's another story. Also a square setup on the wheels/tires is NOT ideal for the 68-72 GM A body because if the absurdly high roll center assuming you're running the stock frame. A staggered setup (about an inch taller and wider in the rear) will out perform a square setup. So if you really want to go with 20s, do it in the rear only and run some 19s in the front which will provide a smaller diameter and allow a little wider tire w/o any hitting or rubbing.
Joe, that was well written and informative and backed up with real life facts. A nice read for anyone interested in maximizing a wheel and tire combo. Thanks!
OP, I can really appreciate your dilemma. Would spacing out your existing wheel a small amount and minor grinding result in sufficient clearance? You could go to a lot of expense and not really gain any additional tire upfront than you have currently. Alternatively, another 18" wheel with a different profile in the inner spoke or barrel could clear, saving a great deal of $$$.
I read your comment on a square setup, which on some cars works well, but the primary aim is to maximize rubber on the front. As mentioned above, our cars can actually handle well with a staggered setup, so maybe you could revisit that idea.
Lastly, 19" wheels do exist, ha ha. A 19x9.5 with a 285/30/19 could squeeze in there without some of the mods a larger combo would need. It is slightly wider but only 25.7 high than what you have now. Please keep us updated, and good luck!
The rear has it's own set of issues but the 20s will be much more forgiving there. You could run 20x10 or 20x11 with a 295 or 305 tire with no issues again with the perfect back space. Of course you could go big money here too and notch the frame and do a mini tub and go all the way to something like a 345 tire but that's another story. Also a square setup on the wheels/tires is NOT ideal for the 68-72 GM A body because if the absurdly high roll center assuming you're running the stock frame. A staggered setup (about an inch taller and wider in the rear) will out perform a square setup. So if you really want to go with 20s, do it in the rear only and run some 19s in the front which will provide a smaller diameter and allow a little wider tire w/o any hitting or rubbing.
-Joe
A little hi-jack here. My 71 is going to have 2" lowering springs and I want to run 18" wheels 18x10 in the back with 305-325 tires. I'll be running C6 brakes with the Camaro backing plates and custom brackets for the front. Do you have any recommendations for tire size or front wheel width?
Unfortunately 2" lowering springs in the rear will make your car handle worse assuming you have the stock GM A body frame. To be clear the stock 68-72 GM A-body has an absurdly high roll center.It is close to twice as high as modern cars. If a 68-72 GM A body is lowered too much with the stock frame (especially in the rear), it won’t corner as well because the already high roll center will actually be moved higher (lowering the rear raises the roll center)making handling MUCH worse. You should only lower the front 2” and the rear 1” to prevent this from happening.I had originally lowered my car 2” front and rear and was unknowingly causing this higher roll center issue. Intuitively you think the lower you go with our cars the better it will handle/corner but that is NOT true with a stock 68-72 GM A-body frame. Note: This does NOT apply to those who go with an aftermarket frame. I’ve seen some high-end Chevelles and other GM A bodies that are really low but since they spent $20k+ on an aftermarket frame they may still be improving their handling by lowering more. For the width front and rear, it's all about your budget and plan for the car. Technically you could do 345s rear and 315s front but you will need a frame notch, minitub, and maybe even fender flares. If you're looking for zero mods with the perfect BS you should be fine with a 305/265 or maybe 305/275 combo on 18x11s rear and 18x10s front.....or 19x11 and 18x10 would work well too (and have better tire options for autocross) and get the correct stagger front to rear that works with the roll center issues. If you want to go wider than 265/275 on the front be ready for massive mods there too on the inner wheel well and fender and the sway bar. The shorter the tire the less work you will have to do.
Unfortunately 2" lowering springs in the rear will make your car handle worse assuming you have the stock GM A body frame. To be clear the stock 68-72 GM A-body has an absurdly high roll center.It is close to twice as high as modern cars. If a 68-72 GM A body is lowered too much with the stock frame (especially in the rear), it won’t corner as well because the already high roll center will actually be moved higher (lowering the rear raises the roll center)making handling MUCH worse. You should only lower the front 2” and the rear 1” to prevent this from happening.I had originally lowered my car 2” front and rear and was unknowingly causing this higher roll center issue. Intuitively you think the lower you go with our cars the better it will handle/corner but that is NOT true with a stock 68-72 GM A-body frame. Note: This does NOT apply to those who go with an aftermarket frame. I’ve seen some high-end Chevelles and other GM A bodies that are really low but since they spent $20k+ on an aftermarket frame they may still be improving their handling by lowering more. For the width front and rear, it's all about your budget and plan for the car. Technically you could do 345s rear and 315s front but you will need a frame notch, minitub, and maybe even fender flares. If you're looking for zero mods with the perfect BS you should be fine with a 305/265 or maybe 305/275 combo on 18x11s rear and 18x10s front.....or 19x11 and 18x10 would work well too (and have better tire options for autocross) and get the correct stagger front to rear that works with the roll center issues. If you want to go wider than 265/275 on the front be ready for massive mods there too on the inner wheel well and fender and the sway bar. The shorter the tire the less work you will have to do.
-Joe
Thanks for the info. No autocross or drag racing, just a street car. I want something that fits without having to modify the car. That and the frame is already powder coated. 19/18 would be better for the roll center issues? 5.5" backspacing is what I want for the back with 11", right. What about the front?
Thanks for the help, hopefully I'll be getting wheels and tires this year.
If you're not looking for all out performance with a drag radial for launching in the rear or autocross tires for hardcore cornering and you haven't invested a fortune in eliminating all the steering and suspension geometry issues with something like the AFX spindles upgrade, adding a fast ratio steering box, and tubular control arms, and custom sway bars etc, then a modest size/width rim and tire that clears your rotors should be fine. No reason to push the limits on anything. I would just go with something like a 275/40/19 rear tire (27.7") on a 19x10 (no reason to go 11" wide on the wheel) and a 245/45/18 front tire (26.7")on a 18x8 wheel on the front and be done with it. BS is different for every car and wheel/tire combo. Different brand tires come in different widths and after market rear ends, rotors, spindles, sway bars etc all change the perfect BS for your setup. If I had to throw out a best guess for your setup and the combo above I would say 5.75ish rear and 5ish front to center in the wheel wells. Also if you buy new wheels make sure you tell them about your rotor and caliper brand and measurements so there is clearance. Happy to share my combo but it may not be right for your setup. I have 13" rotors front and 12" rotors rear and AFX spindles and a custom sway bar in the front:
old setup:18x8 rims 5.25” BS w/245 45 18 Mich P 4S ...note: w/o rotors and spindles would around 4.5 to 5 BS would be better
18x10 rims 6.0” BS w/Nitto*** 555r 305/40/18s.....note w/o rotors or with a thinner tire like a 275-295 5.5 to 5.75 BS would be better
You can spend hours going through it and you will see some Chevelles and other GM A bodies with all kinds of wheel/tire combos. In my opinion a 2" stagger (in both wheel size and tire diameter) front to rear just doesn't look right. The difference is so much the car looks strange from the side view with the front wheel being so much smaller and the rear looking like it's jacked up even when the stance is "perfect" - meaning the top of the wheel wells are hitting the same spot on the wheel/tire front to back (like the Supreme in the picture). But it comes down to what you like. Some really like that raked look with the rear much higher. I believe a 1" stagger front to rear for both wheel size and tire diameter is perfect for 68-72 GM A bodies (meaning 18/19 or 19/20) with the fronts being around 26.5" tall and the rears being around 27.5" tall (1" difference in diameter front to rear). This also happens to be the perfect setup to deal with the roll center issues with the frame (lowering rear 1" and front 2"). That Supreme in your pics has 26" fronts and 28.7" rear (going off your provided tire sizes of 225/45/18 Front 275/40/20 Rear). If those rears were 275/40/19s at 27.6" it would make the car look more "level" and your eye won't notice the 18" vs 20" difference wheel to wheel as much. It would also be better if the fronts were slightly taller.
Oldoldslover is that your 71? Is that why your post about Hurst Olds stripe options? Just curious
Its a 72 cutlass supreme. I like the graphics of the h/o but white isn't my favorite color.
black is ok but i know the body has to be perfect.
I have saddle brown interior, took out power bench and im in the process of installing buckets.
I'm looking for paint ideas to distract myself from reality and its problems....
thanks
Last edited by OldOldsLover; February 20th, 2022 at 05:39 PM.
April 1st, 2021, 08:35 PM
