flash911

First official tech thread started on this forum, so treat the newb kindly please

I've done the reading and still don't have a definitive answer. I have a c5z that I'm prepping for the track. Intended use is HPDE days mostly with some AutoX, but not much (80/20). I've read Zenak's sticky and am pretty sure bushings, motor / trans mounts and coolers will be first on the list. Seats, harness and harness or rollbar will be next. At some point BBK and suspension mods. I figure I'm in for months of cash burn and wrenching.

Onto my question: What size and how big of tires can you fit in the front and rear of a c5z without flaring?

I know Popp runs a 315 / 335 but not sure I need to go quite that big?

I'm 'thinking' 18x10.5 285 or 295 tire front and 18 or 19 x 11.5 rear 315 or 325. I"ll mock up a sway bar and brake ducts for clearance and see how far I can go. I'm pretty sure I know the BS measurement to get close to zero scrub, and a balanced track set up is the goal. I know tuning will be involved no matter what I do, and would prefer to not have too much under or oversteer right out of the gate due to a bad decision on tire sizes.

Whaddaya think?

63Corvette

I think you would benefit from reading some of the prep features on the roadrace and autocross board. Most who are competitive run "square" settup with 305X18 all the way around. This helps with the C5 Corvette tendency to push in lower speed turns. Good luck and post your results.

flash911

Thanks for the response! I've been reading for weeks, still learning but not my first rodeo either.

mountainbiker2

4 C5 Z06 wheels 18x10.5 315/30/18 on all 4 corners. Done.

Steve

flash911

Thanks Steve!

Name's Ron BTW, Sherman Oaks

theseal

I think you'll find that going wide on front track hurts the handling worse than the extra tire warrants. Tuck those fronts in. I think Thomason ran 295's tucked way in on his asp car back in the day.

flash911

Great comment. Too wide and it hurts turn in, which can be tuned to an extent. OTOH, I am not familiar with vette weight distribution and whether these cars 'need' a little extra grip in the rear to stay balanced. Conventional suspension theory says your track car's grip is limited by front tire size, so one would think you'd stuff the biggest tire possible?

(no flames please, this comes from a successful race team owner and suspension guru).

JakeL

Can't speak to always, but for at least a time, (2004-ish) he ran 315/35-17 on the front, and either 315 or 335 in the rear. Ran a real deep backspace, so the wheels would rub at full lock (just had to be careful not to do that). That way, had the best of all worlds - wide wheel, not an overwide front track (for solo), and lots of tire.

I know this because his 17x11.5's and 17x12.5's are on my car still , bought them out at Wendover ProSolo eons ago. IIRC, he sold them to me as he was moving to 18's and a 12" () front, based on his testing showing greater grip. The wheel rub must have been substantial around paddock Been a long time though, I could be misremembering.

Myself, I'm inclined to do something similar, and with the wide front and rear fenders (L5 etc) available these days, try to run a 335 square and see how that does ...

As the earlier posters have said, it would seem that a great way to get to a 90% setup is to get 4 Z06 rears with 315-18's, and go have fun.

Cheers!

-Jake

mountainbiker2

Hi Ron,

Not to far from you. If you need help let me know. I've gone full circle with Corvettes. Mostly Autocross though.

Steve
Before.


Current. Stock C5 Z06.

flash911

Thanks and I'll be in touch Steve. Oh, I've seen your old car before

SunnydayDILYSI

Steve, do you run shims with those? I have 275s up front and am rubbing/wearing on my DRM brake ducts. Do you run without ducts?

flash911

Good question. I think Steve said he runs mostly AutoX, so brakes get minimal heat in 'em. I plan to run roadcourse as well, so ducts are in the plans.

Also Steve what tires are you running? Most 315s want an 11" rim.

Soloontario

I've had smallish 315s ( Nitto NT-01s) on 18 x 10.5" speedline rims at all 4 corners but they provide a lot of rolling resistance and rub a lot.

Likely would be happier with a 295

Last C5

Done twice!!

mountainbiker2

No shims. Just stock 18x10.5 wheels bolted on. Stock ducts. Nothing rubs at all. A regular C5 could be different. I think the Z06 steering rack might have come with a limited stop.

315/30/18 Hoosier A6's. Max out on neg. camber and castor.

JRitt@essex

One of my favorite setups was running rear OEM C5 Z06 18x10.5's at all four corners with 305 Hoosiers. My car was dropped on stock bolts a bit, running T1 front and rear sway bars with 2004 OEM shocks. The edge of the tires came right out flush with fender, but never made contact. On the inside, my tires would just barely kiss my brake ducts (DRM) if I went to full steering lock in the paddock. The mechanical grip with 305's all around was tremendous, and the car was nicely balanced. I never saw the need to go bigger.

As for other mods, I think you're heading down the right track. I ran a Ron Davis radiator/oil cooler. My tranny only ever overheated if I was running in the desert during summer. Otherwise it was okay. That said, a tranny cooler will keep your wear and tear down. The OEM seat is pure *****, and a good seat will put you in touch with the car far better than most other mods. Safety equipment should definitely be a top priority if you like your head attached, and the way it is now. Brakes are my specialty, so when the time comes ask me about that.

Good luck and welcome.

flash911

Thanks JR!

smokinZ1

I'm having L5 rear fenders with the 2 inch lip installed and want to know if anybody can tell me what size wheel combo will fill in extra space? Please include pics if available.

37pat

Has anyone tried the PSS 295/35ZR18s all arond on stock Z06 C5 18 inch wheels? Thoughts? Mostly I'd use as a street setup that I could rotate. Too much "pushing" for the street maybe?

troyguitar

That size is new for the PSS, previously they only came up to 285/35/18 but several people have run the 285's on 4x C5Z rears and liked it just fine. I'd assume 295 would be fine too, it's not much bigger.

To a certain extent I'm of the opinion of "go big or go small" though - in other words either run flared fenders with 335's on 18x12s all around to be as fast as possible or just run whatever is cheapest. I'm going to run whatever's cheapest myself, which means using 4x C5Z fronts at 17x9.5 and probably 255/40/17 Hankook RS3's at $600 or so per set.