Are staggered tires good for autocross?

[ignaro]

I'm in the midst of measuring for the biggest wheels and tires I can fit under my Pontiac Tempest with a full UMI suspension. I'll be adding disc brakes from Kore3 at the same time.

At first I wanted to maximize tire in the rear but as I've struggled to find wheels with perfect offset that are under $400 each, I realized I may want a more square setup since oversteer is preferable to understeer.

Are there any successful autocross GM A-bodies who have a good balance of rear vs front tire contact area?

[65 drop top]

I've always heard it's best to keep the front and rear within 2" of each other. For example, if you can fit an 8" front wheel then you could run a 10" rear wheel. That being said, I'm building a car that'll have a 8.5" or 9" max up front, but will have a 12" rear.

[CampbellshotrodsAZ]

A square setup will always be the "best" way to setup a car for track, or autocross. But due to many factors, it might not be doable. In my case, I'm doing like 65 drop top... my 71 Firebird will have 18x9 up front, and 18x12 out back. Mainly because 9" looks like the biggest I can go up front within the confines of the stock fenders and frame, and 12" fit with minitubs... and I want a car with the steamroller rear tires. I know it's not the ideal setup, but I realize this car will be a lot more of the "touring" aspect of pro-touring... a car I can drive all year, with maybe 6-12 actual race/autocross events a year. I guess one could run a smaller wheel/tire out back to match the front, but as someone coming from drag racing... doing anything but cramming the largest tire I can in the back doesn't come natural to me. :bananna2:

If I feel my tire setup is holding me back, I'll build my 71 Camaro that I know I can get 50/50 balance with. I think getting a balanced car might be more critical, which may be hard on your Tempest.

[ignaro]

doing anything but cramming the largest tire I can in the back doesn't come natural to me.

This is precisely how I feel. On my Tempest, I can fit a 27"x9" tire in the front and a 30"x12" in the back. The problem I'm having is with finding matching wheels that support those sizes. The front can have zero offset which is common with muscle car wheels. The back needs to have the same "front-spacing" between the hub and the inner wheel well lip but I want more depth. This means an 11" wheel would need a +40mm offset which is about 7.5" of backspacing. While there are wheels designed for Corvettes that have the correct bolt pattern and around a +40 offset, there aren't front wheels that match that are 0 offset.... Unless I get custom wheels at $600+ each.

I've started making a database of wheel sizes and offsets. Ultimately I think I'll go with a wheel design I like and 9" wide tires in the front and back. Not as exciting but I can still do 28-30" tall in the back so the profile will still look rad.

This is about what I'm going for (http://www.superchevy.com/features/1010chp-1966-chevrolet-chevelle/). I'll go with more tire and less wheel but the overall dimensions will be similar. His are 19" and 20" wheels, I'd go with 18's or 18/19. I also probably can't fit his 13" width in the back but his 28" height is most likely what I'll go with. These are definitely custom wheels. :\

[Aficionado]

Perhaps an unsophisticated approach, but I just wanted as much tire as I could possibly get on my '72 Corvette autocross car. I wound up with a 305 x 19 front tire and 355 x 19 rear, all tucked under the fenders, but am still building the car so I can't report track results yet.

[ignaro]

That's awesome. What brand and offset are your wheels?

[Turbo6inKY]

The goal in an autocross set-up is to maximize grip at all four corners. A secondary goal is to extend the tires' lives as much as possible, which requires frequent rotation. That always leads to a square setup.

If your A-Body doesn't have a lot of prep, it's going to be nose heavy and very front biased. In that case, you'd actually want bigger tires in the front, because they'll be doing most of the work during the run.

[CSG]

It is usually easier to set up the car with a square setup but you can get a car that is better than most drivers without going square.

[Typhoon1015]

I am on square 275 35 18's on same offset 18x9.5 wheels. I use wheel spacers to be able to tune my turning radius and fender clearances. I can rotate f/r wheels if needed. If I had the option for larger, I would go larger all around.

[Slick68]

I asked a similar question when ordering my new wheels last year. The response was overwhelmingly for a square setup.
https://www.pro-touring.com/threads/119745-New-wheels-coming-Which-tires

[USAZR1]

This is precisely how I feel. On my Tempest, I can fit a 27"x9" tire in the front and a 30"x12" in the back. The problem I'm having is with finding matching wheels that support those sizes. The front can have zero offset which is common with muscle car wheels. The back needs to have the same "front-spacing" between the hub and the inner wheel well lip but I want more depth. This means an 11" wheel would need a +40mm offset which is about 7.5" of backspacing. While there are wheels designed for Corvettes that have the correct bolt pattern and around a +40 offset, there aren't front wheels that match that are 0 offset.... Unless I get custom wheels at $600+ each.

I've started making a database of wheel sizes and offsets. Ultimately I think I'll go with a wheel design I like and 9" wide tires in the front and back. Not as exciting but I can still do 28-30" tall in the back so the profile will still look rad.

This is about what I'm going for (http://www.superchevy.com/features/1010chp-1966-chevrolet-chevelle/). I'll go with more tire and less wheel but the overall dimensions will be similar. His are 19" and 20" wheels, I'd go with 18's or 18/19. I also probably can't fit his 13" width in the back but his 28" height is most likely what I'll go with. These are definitely custom wheels. :\


If your 66 has not been minitubbed, how are you going to fit an 18 or 19x11 rear wheel w/o clearance issues? What 18" or 19" performance tire has a 28" diameter?

[Schwartz Performance]

Our 1965 Tempest has been running 275 & 335 for 8 years and has been pretty competitive. In my opinion, a 275 square setup would be worse then what we have now. It has awesome rear grip and doesn't tend to push.
We do have our G-Machine Chassis on it, and BFG Rival S tires now, but this combo works well!
Maybe some day we will throw 315's up front & see what the difference is :P

-Dale

[ignaro]

If your 66 has not been minitubbed, how are you going to fit an 18 or 19x11 rear wheel w/o clearance issues? What 18" or 19" performance tire has a 28" diameter?

I meant that those dimensions can fit. I'm building a database of wheels and tires now to see what I can get to work.

Not sure, maybe I can't... The sidewall bulge on my current 225/70r14s gives me just over 9" wide. The tire is right up against the wheel well which I'll likely cut and smooth vertical to the quarter panel. On the inside I've got 2.75 between the sidewall and frame. I may not run an 11" wheel but I should be able to fit that much tire.

I'd like to go with something similar to Schwartz's recommendation of 275 and 335 but I'll probably have to step down a notch from there and keep a similar ratio.

[ignaro]

I asked a similar question when ordering my new wheels last year. The response was overwhelmingly for a square setup.
https://www.pro-touring.com/threads/119745-New-wheels-coming-Which-tires

Thanks, I searched but hadn't seen that thread

[JustJohn]

Isn't this car kind of notable for decent handling in spite of staggered tires?
142221

[dontlifttoshift]

Yep, with 60% of the weight over the _rear_ wheels.

[CampbellshotrodsAZ]

Probably a better example of staggered tires on a performance car is the Viper ACR. I was at Bondurant earlier this year and surprised to see 355's out back, with 295's (I believe) up front. That doesn't quite follow the convention of staying within 50mm that I've heard. Front engine, but 50/50 balance from what I just looked up.

[JustJohn]

Yep, with 60% of the weight over the _rear_ wheels.

Details...

[gator68428]

I'm not sure if asking whether or not staggered is the right question. With these front heavy cars, the performance answer is: As big as a front tire as you can fit.

It's pretty typical to get 315s to 335s out back. If you get anywhere close to that in the front your car will handle turns like a beast if setup properly otherwise. If can't do 315s up front, at least target 275s.
Need to do at least as big out back. Wouldn't help much to go staggered (bigger out back) on AutoX, but it wouldn't hurt much either I would guess. But it looks cool. And would help if you ever go to the drag strip... P-t cars are all around cars that are meant to do many things so why not.

I recently upgraded to 315s all around in my 68 Firebird. The TCI front clip made that possible without outer fender mods (just rolling the lip, and inner fender mods). Made me more competitive for sure.

[ignaro]

With these front heavy cars, the performance answer is: As big as a front tire as you can fit..

That's really interesting. I checked out the fronts again today and I do have quite a bit of clearance. It's really hard to tell and measure accurately with tiny-radius wheels. It doesn't look like my Tempest would require fender mods-- I'll search for the biggest fitment I can in the front and that'll likely be good enough for the rear. I'd certainly rather have oversteer than understeer.

There's no downside to having 3" taller tire though, right? It can't increase the contact patch _that_ much.... Looks-wise, staggered height is what I'm really after.

[gator68428]

That's really interesting. I checked out the fronts again today and I do have quite a bit of clearance. It's really hard to tell and measure accurately with tiny-radius wheels. It doesn't look like my Tempest would require fender mods-- I'll search for the biggest fitment I can in the front and that'll likely be good enough for the rear. I'd certainly rather have oversteer than understeer.

There's no downside to having 3" taller tire though, right? It can't increase the contact patch _that_ much.... Looks-wise, staggered height is what I'm really after.

By "big" I meant wide. The diameters of the tires I'm referring to are all around 25". Whether its a 245/40, a 275/35 or a 315/30, on an 18" wheel (most common for tire selection) they're all about 25" in diameter. When i had staggered setup i still had 18s all around. When i first got late model wheels i had 245/40 up front 275/35 outback. Then i went to 275/35 square. Then minitubbed out back and went to 315/30s staggered. Then played with the 315s up front and did the mods and now am 315 square.

A 3" diameter difference sounds like a lot BTW.

[silo84]

1968-1972 GM A-bodies
I used this for my second gen Camaro as a base line


http://www.hotrod.com/how-to/wheels-tires/fitting-tires-wheels/

1968-1972 GM A-bodies

15-inch: 15×8 with 4-1/2-inch back-spacing front and rear. Use 255/60 tires.

16-inch: 16×8 with 4-1/2-inch back-spacing front and rear. Use 255/50 tires.

17-inch: 17×91/2-inch with 5-1/2-inch backspacing front, 17×11 with 5-1/2-inch backspacing rear. Use 275/40 front tires and 315/35 rear. This is tight in the rear.

18-inch: Same as 17-inch.

[Slick68]

That's really interesting. I checked out the fronts again today and I do have quite a bit of clearance. It's really hard to tell and measure accurately with tiny-radius wheels. It doesn't look like my Tempest would require fender mods-- I'll search for the biggest fitment I can in the front and that'll likely be good enough for the rear. I'd certainly rather have oversteer than understeer.

There's no downside to having 3" taller tire though, right? It can't increase the contact patch _that_ much.... Looks-wise, staggered height is what I'm really after.

Staggered height for autocross? NO!!! Before I got my new wheels in a square setup on my truck, I had 17x8 255/50/17 front, 17x9.5 275/55/17 rear. There's about a 2" difference in tire height. It looked good, but didn't perform all that well. At my first event with the new, squared wheel/tire combo, guys at the event kept complimenting how much better the truck was handling compared to past events. They said the truck was much flatter in the turns. I went from being at the bottom of the times, to finally running somewhat average times. They said whatever I had changed since last year was really showing.

All I did was change wheels/tires!!!

From what I've learned, the offset height of the tires was distributing the weight differently. Also, the larger tire in the rear had more sidewall to roll. That's why a wider rear tire with the same height is still common and works.

[ignaro]

Staggered height for autocross? NO!!!

Ah, I see!

It's too bad that I'm having to choose between the look and rake I want and performance. Not totally surprising, I suppose. On the A-bodies, I really don't like the way square wheels looks. Perhaps I'll go mildly staggered diameter...? The research continues.

[CampbellshotrodsAZ]

How vital is autocross performance for you? All of our cars are going to have certain balances where to have to prioritize what's most important. If you think you're going to autocross maybe 4 times a year at a casual participant, I'd definitely go with a 28" tall tire in the back of that Tempest. It will definitely look better in those large wheelwells, IMO. I have a 66 GTO that I'll be building in the somewhat distant future, but I'll be going more "restomod" since I want it to look cool first off, ultimate track capabilities will be second in line. You aren't going to have a perfectly balanced autocross champion, so I wouldn't stress about it much at all.

[ignaro]

How vital is autocross performance for you?... I'd definitely go with a 28" tall tire in the back of that Tempest. It will definitely look better in those large wheelwells, IMO.

Still researching size options from different wheel and tire manufacturers. I'll definitely be going with a taller tire in the back since those wheel wells are so big. Width is a different issue. I plan to drive spiritedly through the canyons in LA. Understeer would literally be deadly so I don't want a fatter drag race tire in back. Trying to find a good tire combo thats around 275 width front and back with a 26" and a 28"+...