Btrav1226

I tried to search this but came up empty so please excuse me if this has been discussed. I run 18 inch 315f 335r 888r on a c7 GS for my track setup. From what i gather 35psi hot seems to be a good target to start. However, I've noticed that im not getting tire wear all the way to the small "triangle indicator" on the sidewall. Is this important? Does that mean I'm running too much pressure? I've seen a max hot of 37 psi but then I bleed to 35 psi right after the session. So I'm usually starting the next session around 31 psi or so, tires not fully cool. Also, car is aligned to the DSC sport street/track specs. I guess my main question is to those of you who run 888r, are you seeing the tires wear right up to the triangle indicator and what psi are you using to get it there? Or should i just forget about that indicator? Thanks

STANG KILLA SS

i ran the 888R. same 315/335. hated them. i had same experience. i too was aiming for 32-34 hot, and was not getting anywhere close to sidewall arrows, and also wearing the center of the tire first (ie over inflated)
i found 30 psi to be the best for grip. and for proper wear patterns.
watching TPMS on track the second i would hit 31psi and above, the tires would start sliding and shutter and grip would fall off a cliff.
30psi seemed to be the key to getting everything out of that tire.

i did a ton of testing with these tires. tryed everything from 26-42 psi.

in the end i hated every session of everyday with those tires. coming from Rival S, and then going back to rival S after.
with same driver, same track, same car, same setup, same tires sizes, and same conditions and temperature. the Rival S was 1.8 seconds faster, and just MUCH higher grip everywhere. the R888R acted alot like a street tire. where the Rival S acted like a proper R compound.

i found many others had the same expereince as me. usually in heavier / high HP cars. all disliked the R888R.
however i found that many of the lighter, lower HP car owners loved them.

rbl

I know I'm outdated on the 888's and maybe they changed the compound. I ran low cycle scrubs on my C6 and found they had good grip at 40 Psi. After close to 2 years on the tires and probably 25+ track days I finally ended up starting around 35 Psi. Most all of the track time was at VIR and it is pretty easy on the tires.

harrydirty

Same experience with the 888R, 335 rear.......running about 35psi hot, but would actually feel better when I first went out when tires were 30-31 psi. Problem was had to drive to track and could not run with cold pressure lower than 25psi, otherwise would trigger error/limp mode. Usually started from home with pressures in 27-28psi region to get to 35psi hot (approx.). I suppose I could have bled air during the day to keep pressures closer to 30psi hot, but then would have to refill before going home. Noticed that middle of tire wore before sides on my rear 335 tire, indicating over-inflation.

Now trying NT01 this season.

Mark Leger

What would be the best pressure for running 315 rivals upfront and 335 rivals out back?

TCorzett

I target 32-34 hot... above that things feel a bit slippy.

Btrav1226

So has anyone running 888r’s actually gotten the wear all the way to the triangle marker? Sounds like a “no”

harrydirty

On my front 295's yes, but not so much on my 335 rears; it was close, but the middle wore out way before the edges/sides. Interestingly, the fronts were fine.

Btrav1226

Hmm. So maybe the wear markers work better on narrower tires. The 315 and 335 are the wider if not widest sizes in those tires. Maybe the wear markers are optimized for the average sized width and not specific to each size if that makes sense? IE maybe on a 275ish tire the wear marker would be accurate but on a 315 or 335 its just so wide that its not accurate. I bet a pyrometer would help. Ugh

Kubs

Tire pressures are track and vehicle specific, and can vary based on alignment, temperature, weight, etc. Pressures should be set by taking tire temps at the track. The wear pattern should confirm your settings are correct. If you are wearing the center you have too much pressure. If you are wearing the inside or outside more you either have too little pressure, too much toe, or a combination.

Kubs

Keep in mind the wider you go on the same vehicle changes the footprint of the tire and you will have to compensate with pressure. The footprint area will not change for the same weight and inflation, but the shape will. Going from a narrow tire to a wide tire at the same pressure will make the footprint wider, but much shorter in length. Reducing inflation on the wider tire will get you closer to the same of the narrow tire.

Also, the little triangle on the side of the tread is not a wear indicator, it shows you where the tread wear indicators are located within the tread itself. Using those as a gauge to set pressure is not correct.

andersnor

I ran 26PSI cold and 31-33PSI hot now last trackday.

STANG KILLA SS

i agree with 32-34 for rival S. i usually run 34 just to help shoulder wear a tad.

fuggles

I run 315 square on my C5z. Wear looks good to just past the point of the triangle. Nice and even across the tire. I start around 26 cold in the morning and bleed off through the afternoon. Thunderhill gets pretty hot in the afternoon. I'm running a mild alignment of 1.9 f and 1.2 r. Stock springs with delrin bushings.

BrunoTheMellow

Yes. To the tip was my target. On a c7 z51 with z06 springs I got 255/295 to the wear triangles at 35 hot. And on 295/305 the same. I targeted 33 the last time I ran the tires. Had good results. 35 hot was sticky for me but the first track day was 1 second faster than subsequent days

BrunoTheMellow

Wait. What. These comments don't make sense. Higher inflation = less contact patch.

Manufacturers have started using the side markers for years as the "edge" of the treads. It's perfectly fine to use them to gauge tire roll-over.

BrunoTheMellow

Over inflated rears if the edges wore equally.

Btrav1226

Ok i have my first time trial coming up this weekend. First day is a DE “practice” so to speak. I’m gonna try going down to 33psi hot and see how that works. Also, It’s supposed to be around 100 degrees and sunny both days so I think I’ll have to really stay on top of the pressures.

Kubs

What doesn't make sense? Yes, the contact patch at 35psi is smaller than at 30psi. The car weight and the inflation pressure determine the shape of the contact patch. The total AREA of the contact patch is the same (both at 30psi), but it will not perform in the same way for a wider tire. By going to a wider tire and keeping the same inflation pressure the contact patch gets wider side to side but is shorter front to back. You would need to lower the inflation pressure to gain the length back.

It is OK to have the shoulder of the tread contact the ground under cornering, but that is not why those triangle markers are on there. They are a government regulation to show where the tread wear indicator on the tread are located. Their purpose is not for setting inflation pressure.

Btrav1226

What are your pressures hot? Do you take measurements immediately after a session? You said you bleed off through the afternoon but is there a specific hot target you aim for?