catwood

Running at willowsprings for the first time in this car. 275 fronts, 305 rears shaved toyo R888. Car's bone stock.

What's a good cold pressure pressure to start with?

I'll be taking temps and adjusting as the day goes on, just debating a place to start. My last car liked about 28 or 29 lbs dead cold but it had bigger tires and was heavier.

Thanks

JimbeauZ06

Maybe you'll hear from someone running Toyo's but if not I start my Nittos (similar compound to the R888) at 28 in cool weather (50s-60s) and then drop starting temps from there based on increasing outside temps. I generally run higher pressures in cool/rain but no more than 30lbs. I've heard of others starting Nittos as high as 34lbs but that's way too high IMHO for normal temp ranges IMO.

Last year at Daytona (90 degrees in Oct) I started with 24 front and 26 rear.

Regardless of starting pressure I'm looking for a hot pressure of no more than 38lbs.

You'll find a lot of guys getting a lot more scientific than that with IR temps etc, but I'm not racing.

gkmccready

http://www.aimtire.com/typ_category.asp?ObjectID=6828

R888s like a pretty high hot pressure. Aim for at least 40psi hot and you may find 42-45 even better. The Nitto 555RII is more like a Toyo RA1 than an R888. I've been starting at around 36psi and ending up low- mid-40s and the tires have worked well.

I used to run then starting at 28psi ended around 36-38psi and then Ron@AIM told me to bump up the pressures and the tires just continued to get better every time I added a pound. So, like I said, I now start at 36psi or so cold and things work well. To be honest, I haven't tried starting any higher since I'm already ending up hot at 42-45psi.

I'm in a C6 with some mods, including 18x10+18x11 CCWs running 275/35r18+305/35r18 R888s.

catwood

Thanks, that's good info.

DRUGschnorr

would i apply this same logic to as set of Yoko's 255/35 R18 and 305/30 R19? I have been doing HPDE for 4 months and loving it.....the first weekend in feb was 40 degrees and i started at 36lbs
now that it heats up i have been starting at 34 and immediately when i park i read 39-40 in the front and 38-39 in the rear.. so i should consider boosting by 1-2lbs this weekend.

wonder when the temps in TX start hovering around 95-100 for our balmy summer..

I do love changeing brakes but the C6 is a BIG *** BUCKET OF FUN ON THE TRACK..
-tomtom

AlwaysInBoost

I just finished a 2-day event running on R888's for the first time and was not a happy camper. Coming from RII's, the R888's have a lot less grip IMO. It took me a while to find a pressure that worked for my setup (stock suspension w/265/35/18 front & 305/35/18 rear on C5Z rears all around), but IMO they feel the most stable around 36 hot. I would start the rears @ 30.5psi cold and the front @ 32 and would finish with 36 rear and 38 front HOT. at that pressue I was just on the shoulder of the rears, but that was the only way they felt stable. I tried pressures as high as 43 HOT and everything in between, but ultimatley any higher pressures then 36 hot in the rear and the car was too loose for my taste.

Overall I felt they had little grip and were not confidence inspiring. It could have been due to the fact the tires I was running were previously used. I purchased a couple pairs of scrubs from a vendor on here who said they were shaved and had only 1 40min heat cycle on them. the way they handled made me feel like they were already heat cycled out.

gkmccready

No. Setting pressures varies by tire. As mentioned above, even two DOT-R tires from the same manufacturer wants different care and feeding.

longdaddy

r888s have ridiculously sharp drop-off in traction once they reach a certain number of heat cycles. i would never buy these tires anything other than brand new with stickers.

AlwaysInBoost

but would 1 - 40 minute heat cycle on a shaved tire be enough to heat cycle them out?

gkmccready

So, I've never had 555RIIs, but I have gone through a lot of RA1s on different cars. The C6 has only had R888s on it other than the stock tires. Both sets of R888s went on brand new and they didn't suffer the RA1 problem of being really, really slippery at full tread depth. I've never followed it with lap times, but I ran the R888s down to nothing in the rear, and I've run RA1s to the cord many times [on other vehicles] -- they just get better and don't seem to heat cycle out like the stickier DOT-Rs.

I daily drive the R888s on my C6 as well as taking it to the track. My biggest complaint? The road noise is insanely bad. It's a constant whir. Couldn't care less on track, but taking the wife out to dinner 30 miles away down the highway the noise gets annoying.

I've found the R888s to offer great grip, and great tire life, they easily pull 1.2+G around T2 at Thunderhill. No muss, no fuss, no nothing.

For daily driving, just like at the track, I just start the pressures at 36psi. Seems to get good wear. At the track, same starting pressures end up mid-40s and also provide good wear, and good grip.

Hopefully you just got a bit unlucky with a set...

gkmccready

Any idea where that occurs? I ran through most of a 295/30r18 front, and pretty much all of a 305/35r18 rear and never really found that. And that included several thousand street miles, including a drive from SF to Spring Mountain and back, along with several track days at Thunderhill which is something like 350mi roundtrip, plus back and forth to work and whatnot...

longdaddy

5 track days and about 1700 hwy miles for me. On the 6th day I started experiencing heavy understeer when I would go into 2nd gear corners at my usual speeds. Tires still had about 2/32nd tread depth in the front (maybe a little more). Talked to local club racers who use this as spec tire and they have confirmed sharp drop-off, one of them mentioned that the sanctioning body is considering going back to RA-1 because of heat cycles vs traction issues. the class is budget oriented so having to refresh the tires often to stay competetive is a big deal for them.

gkmccready

Guess I'll keep an eye out for it, but my first set of R888s had 8000mi and 20+ twenty minute sessions on them and didn't show these signs. But I have been told over the years that I'm very easy on tires... of course, I'm only turning 2:07s at Thunderhill for a track day pace, not the 2:low or 2:flat the V710 & Hoosier guys are running.

catwood

Well this is the first time for me out in the vette. I'm hoping to run better than a :40 but it really doesn't matter as this is just to establish a baseline for modding it later.