autocross wheels and tires for a c4
03-15-2011, 11:27 AM
#1
Intermediate
Thread Starter
autocross wheels and tires for a c4
hi all
have to buy new wheels and tires for my race car (91 roadster) the past few years have been running stock 3 but am stepping up to to super stock this year in the past i have been running yokahama a008 295 35 18 on 9.5 in wheels the new class allows me to run r comps most guys run 315 s all round i have been thinking of running a stagerd set up has any one out there tried this and how did it work
tks
have to buy new wheels and tires for my race car (91 roadster) the past few years have been running stock 3 but am stepping up to to super stock this year in the past i have been running yokahama a008 295 35 18 on 9.5 in wheels the new class allows me to run r comps most guys run 315 s all round i have been thinking of running a stagerd set up has any one out there tried this and how did it work
tks
03-15-2011, 11:48 AM
#2
Le Mans Master
I ran stock sized C5 ZO6 wheels for 4 races last year, 295/35/17 and 315/35/18 on used up Kumho 710s that a friend game me, and it was an absolute blast! I prefer a staggered setup, but I'm still learning and it's nice to have a tad of understeer vs oversteer...for now.
03-15-2011, 02:07 PM
#3
Le Mans Master
Member Since: Oct 2007
Location: Akron Ohio
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2023 C5 of the Year Finalist - Modified
2022 C5 of the Year Finalist - Modified
St. Jude Donor '09-'10-'11
I run the same setup on my car for autocross and road racing because I focus more on roadracing and just kinda "show up" for an autocross. that said, I run the same size on front and rear because the car seems to handle better on the road course that way, but it does well in an autocross too.
On a side note, what type of wheels were the 18x9.5s? If you go with wider ones and decide to sell let me know, Im looking for some 18x9.5 wheels.
On a side note, what type of wheels were the 18x9.5s? If you go with wider ones and decide to sell let me know, Im looking for some 18x9.5 wheels.
03-15-2011, 04:10 PM
#4
Melting Slicks
I run 315s on all four. Seems to balance the car with the rest of the set up. It may just be my driving style or set up or whatever but when I tried staggered 18s the car didn't seem as responsive. Just my two cents of course.
03-15-2011, 07:00 PM
#5
Melting Slicks
We found that a square setup works a lot better on C4's.
The reason for that is that you can't put too much roll stiffness into the rear of a C4 or it starts to jack. Since you can't put more roll stiffness in the rear, you can't properly balance the car with bigger tires on the back than on the front. If were to just put bigger tires on the back it would push like a pig.
With a square setup you can take advantage more front roll stiffness and the car will stay balanced.
We tried bigger rear tires on the back of our BSP car and couldn't get rid of the push.
We went with 315's all around and that worked the best.
Maybe if you aren't using R comp kinds of tires you could get away with it, but if you are using Kumho's or Hoosiers, you really can't
The reason for that is that you can't put too much roll stiffness into the rear of a C4 or it starts to jack. Since you can't put more roll stiffness in the rear, you can't properly balance the car with bigger tires on the back than on the front. If were to just put bigger tires on the back it would push like a pig.
With a square setup you can take advantage more front roll stiffness and the car will stay balanced.
We tried bigger rear tires on the back of our BSP car and couldn't get rid of the push.
We went with 315's all around and that worked the best.
Maybe if you aren't using R comp kinds of tires you could get away with it, but if you are using Kumho's or Hoosiers, you really can't
03-16-2011, 11:42 AM
#7
Melting Slicks
We found that a square setup works a lot better on C4's.
The reason for that is that you can't put too much roll stiffness into the rear of a C4 or it starts to jack. Since you can't put more roll stiffness in the rear, you can't properly balance the car with bigger tires on the back than on the front. If were to just put bigger tires on the back it would push like a pig.
With a square setup you can take advantage more front roll stiffness and the car will stay balanced.
We tried bigger rear tires on the back of our BSP car and couldn't get rid of the push.
We went with 315's all around and that worked the best.
Maybe if you aren't using R comp kinds of tires you could get away with it, but if you are using Kumho's or Hoosiers, you really can't
The reason for that is that you can't put too much roll stiffness into the rear of a C4 or it starts to jack. Since you can't put more roll stiffness in the rear, you can't properly balance the car with bigger tires on the back than on the front. If were to just put bigger tires on the back it would push like a pig.
With a square setup you can take advantage more front roll stiffness and the car will stay balanced.
We tried bigger rear tires on the back of our BSP car and couldn't get rid of the push.
We went with 315's all around and that worked the best.
Maybe if you aren't using R comp kinds of tires you could get away with it, but if you are using Kumho's or Hoosiers, you really can't
He said it a lot better than I did.
03-16-2011, 12:41 PM
#8
Safety Car
I run CCW Classics with 11.5" front and 12" rear.
Tires are Goodyear Eagles,
25.5"x11.5"x18"
25.5"x12"x18"
I don't have any handling issues with it. I like the way the car handles with this arrangement.
As a comparison, I have full interior with roll bar and ALL the stock stuff in the car (including A/C). My 355 TPI is pushing 425 HP/525 lb.ft. With this particular setup I was .5 seconds off 2 SpeedGT Corvettes @ TWS. I gave up a good 400+ pounds on them, as well as 100 HP. One was an LT4, the other an LS6 (a '96 and one of the original Z06 "kits"). I surprised them...they even came over to my pit and had a look in, around, over and under after I set my lap times.
CCW is definitely the way to go with track wheels. My set of Classics new were $1,800. John even sent me 2 test wheels (with tires) to see if the back space was going to work. Custom 3-piece forged wheels are hard to beat. They can tweak your backspace to fit almost anything.
Granted, the same sized tires front/rear makes it easier to rotate tires and get better wear from them. The setup I run was the same they used on the C5R's...and they didn't do so bad on track
Tires are Goodyear Eagles,
25.5"x11.5"x18"
25.5"x12"x18"
I don't have any handling issues with it. I like the way the car handles with this arrangement.
As a comparison, I have full interior with roll bar and ALL the stock stuff in the car (including A/C). My 355 TPI is pushing 425 HP/525 lb.ft. With this particular setup I was .5 seconds off 2 SpeedGT Corvettes @ TWS. I gave up a good 400+ pounds on them, as well as 100 HP. One was an LT4, the other an LS6 (a '96 and one of the original Z06 "kits"). I surprised them...they even came over to my pit and had a look in, around, over and under after I set my lap times.
CCW is definitely the way to go with track wheels. My set of Classics new were $1,800. John even sent me 2 test wheels (with tires) to see if the back space was going to work. Custom 3-piece forged wheels are hard to beat. They can tweak your backspace to fit almost anything.
Granted, the same sized tires front/rear makes it easier to rotate tires and get better wear from them. The setup I run was the same they used on the C5R's...and they didn't do so bad on track
03-16-2011, 01:39 PM
#9
Melting Slicks
With my limited experience I hate to even suggest that what I experienced was setup vs driver error but I have to think (and want to think 
) that the setup played a big part in my severe understeer.
After 4 HPDE days and one autox day in my Z51 85 running 335/18 rears and 285/18 front street tires the push had become unbearable. I went to the next autox with my other setup 17x10 with 275/40 (street tire) on all 4. The car was definitely more "balanced", in that mistakes led to sometimes understeer and sometimes oversteer. So I wasn't faster but the car definitely behaved different. I hope that makes sense.
My plan is to swap the inner barrels of the 18" CCWs and at least be able to run 315s up front with the 335s out back. I bought the CCWs many years ago off a ZR1, they are 12.5 in the back and 10.5 up front. Swapping the barrels will give me 12rr and 11fr.
) that the setup played a big part in my severe understeer. After 4 HPDE days and one autox day in my Z51 85 running 335/18 rears and 285/18 front street tires the push had become unbearable. I went to the next autox with my other setup 17x10 with 275/40 (street tire) on all 4. The car was definitely more "balanced", in that mistakes led to sometimes understeer and sometimes oversteer. So I wasn't faster but the car definitely behaved different. I hope that makes sense.
My plan is to swap the inner barrels of the 18" CCWs and at least be able to run 315s up front with the 335s out back. I bought the CCWs many years ago off a ZR1, they are 12.5 in the back and 10.5 up front. Swapping the barrels will give me 12rr and 11fr.
03-16-2011, 09:48 PM
#10
Intermediate
Thread Starter
thanks for all the input i will be running r comps i think a6 hossiers i think i will run 315s all round and buy some new wheels but will keep the setup i have now for rains, the wheels i run now are just 2001-2 rear wagon wheels 18.5 lbs and tough as nails & cheep as chips
thanks to all
dan
thanks to all
dan
