When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
First autocross this Sunday with my new to me 100% stock suspension/alignment C7 GS with 315/335 18's RE71 RZ. Last car was a C5Z with 315x18 square RT660's I ran around 32FR 30RR
Just looking for some ballpark pressure recommendations. My normal approach I found worked has always been the rear pressure was 2psi lower than fronts and to eyeball the wear around the shoulder given the course setup that day.
I run 295/30/18-335/30/18 RZ's, cold 28/28, hot 30/30, C7 Grand Sport, stock suspension except for AFE Front Sway bar.
Awesome, thanks. Have you tried staggered pressures? Or reason behind front/rear the same?
Did you notice a big improvement with larger front bar? I did similar on my C5Z running a C6 Zr1 front bar being the largest factory bar that would bolt on. Worked well, cheap too lol
I do autox and time trials on track. I had both AFE F/R bars, felt good, then added 2650 Magnuson S/C, so went back to stock rear bar to settle down the rear and put down power better.
I've run C5Z06 for 10 years, always ran 2 psi more in front, I starting running equal pressure with C7GS for track 25/25 cold, didn't want to go lower in the rear to set off TPMS warning, and it works. But 30/28 should be good for autox, too.
I do autox and time trials on track. I had both AFE F/R bars, felt good, then added 2650 Magnuson S/C, so went back to stock rear bar to settle down the rear and put down power better.
I've run C5Z06 for 10 years, always ran 2 psi more in front, I starting running equal pressure with C7GS for track 25/25 cold, didn't want to go lower in the rear to set off TPMS warning, and it works. But 30/28 should be good for autox, too.
How do you like the new RZ’s and what width wheels do you have them mounted on?
First autocross this Sunday with my new to me 100% stock suspension/alignment C7 GS with 315/335 18's RE71 RZ. Last car was a C5Z with 315x18 square RT660's I ran around 32FR 30RR
Just looking for some ballpark pressure recommendations. My normal approach I found worked has always been the rear pressure was 2psi lower than fronts and to eyeball the wear around the shoulder given the course setup that day.
I also ran lower rear psi than front with staggered tires because if the car has 50/50 weight distribution then the narrower fronts have more weight per sq in I figured though I also ran slightly more camber in the front than rear. What width rims do you have the 315/335 tires mounted on?
I also ran lower rear psi than front with staggered tires because if the car has 50/50 weight distribution then the narrower fronts have more weight per sq in I figured though I also ran slightly more camber in the front than rear. What width rims do you have the 315/335 tires mounted on?
18x11 front and 18x12.5 rear. Stock alignment and stock ride height.
My normal "simple approach" is to see where the tire wears/rolls over given the current course layout and adjust pressures based on that also factoring in how it feels and it does what I want/expect which increases confidence to push.
I do have a pyrometer to be "technical" but it rarely comes out. My past C5Z on triple adj coilovers had more ***** to tweak. This car is 100% stock suspension so, toss it in Race mode and do away with any nannies and let it eat.
Last edited by smitty2919; Apr 9, 2026 at 09:01 AM.
18x11 front and 18x12.5 rear. Stock alignment and stock ride height.
My normal "simple approach" is to see where the tire wears/rolls over given the current course layout and adjust pressures based on that also factoring in how it feels and it does what I want/expect which increases confidence to push.
I do have a pyrometer to be "technical" but it rarely comes out. My past C5Z on triple adj coilovers had more ***** to tweak. This car is 100% stock suspension so, toss it in Race mode and do away with any nannies and let it eat.
I like it and I have the same wheels, was debating on whether to go 315’s or 295’s up front. Have run 295 RE71RS and A052 on 10” and 305 RE71RS and 315 CRS on 11” wheels, but not 295’s on 11” though thinking back my C5FRC had 295 on 10.5” in the rear originally.
I will stuff as much tire as I can. Some school of thought is a lack of response with a tire that is pinched (315 on a 10.5). And that makes sense.
I also hate the stretched look but that seems to be the more “optimal” approach.
My C5z was 315 square on 10.5 RT660’s also to be able to rotate. The GS I have found many say stick to a staggered while also not deviating TOO far from OEM diameter so all the drive modes remain relatively happy.
I will stuff as much tire as I can. Some school of thought is a lack of response with a tire that is pinched (315 on a 10.5). And that makes sense.
I also hate the stretched look but that seems to be the more “optimal” approach.
My C5z was 315 square on 10.5 RT660’s also to be able to rotate. The GS I have found many say stick to a staggered while also not deviating TOO far from OEM diameter so all the drive modes remain relatively happy.
I don’t like the stretched look mostly because it doesn’t protect the rim, but pinched tire could just be more rotational weight which isn’t good.
I’m not concerned about stability control as I turn it off, but do want to keep ABS happy and feel the car handles better with a stagger personally.
Really interested hearing how these tires work out on track for C7 GS/Z06. I was tempted to buy a set but decided to hold off and wait for some reviews.
Really interested hearing how these tires work out on track for C7 GS/Z06. I was tempted to buy a set but decided to hold off and wait for some reviews.
From what I gather within my crowd/group...they are preeeety good. Reported to be better than the RT660's I had before.
From what I gather within my crowd/group...they are preeeety good. Reported to be better than the RT660's I had before.
Nankang CRS are also pretty good.
Nankang CR-S v2 and Supercar3R are my current go-to for HPDE so glad to have a new entrant in the same sizes I run. 305/30/19, 325/30/19 Hoping they're as good or better than CR-S. I really liked the RE71RS on other cars, but they never came in the sizing I needed for the C7Z.
Nankang CR-S v2 and Supercar3R are my current go-to for HPDE so glad to have a new entrant in the same sizes I run. 305/30/19, 325/30/19 Hoping they're as good or better than CR-S. I really liked the RE71RS on other cars, but they never came in the sizing I needed for the C7Z.
Yep, that's why I went down to 18's.It was an ordeal going through my head. 18 square...18 staggered...19 square...19 staggered...18/19 combo...
First event I ran 29psi square and the second event I ran 32FR/30RR and may stick with the 32/30 going forward. They give a little audible feedback if pushed too hard which I like.
C7 GS RE71 RZ pressures
