mwneedham

Just ordered my first set of R-888's as the RA-1's are no longer available in my size. Have been running the following pressures hot at the track: front is 35psig and rears 38 psig on Pilot Sports. (Not cups). With the R compound tires, are these pressures a good starting point? Tire size is 225/40 and 265/35.

Thanks for the help.

MWN

race911

Can't really go wrong from a baseline to optimize at 38 hot all around.

Lots depends on how the rest of the car is set up, and your driving style. Not to mention where you are in the food chain--cruising briskly, or lap record holder. Ultimately, documenting tire temps is the only way to figure out exactly. I've never run 888s, and with the fiascos dealt with when the various racing series I'm involved with/close to (SM, Spec 911) I've avoided using them. But absolute pressure-wise, I never heard the guys at the front end of the grid deviating from RA1 pressures.

Jimjacqmx5

Hmm interesting, I've never used R-888's but with the Dunlop Dz03G's I run 32 hot. Any hotter and the middle of the tyre gets hammered. I would ask the supplier of the tyres who I assume is a motorsport tyre specialist and familiar with that specific tyre.

boxsey911

Are you talking about 17 inch though Jim? The cold pressures of 18 inch tyres are recommended to be higher than the 17s, hence I think hot pressures for track will also be higher?

NineMeister

Tyre pressures should be adjusted to give an even temperature spread across the tyre when hot. The R888 will require less pressure than a Michelin Cup, so I recommend that you start with 30 front 32 rear cold, monitor the pressure as they warm up and drop the pressure if the centres run hot.

By even temperature spread, in an ideal world you would have (for instance) 35/35/35 C measured on the outside/centre/inside, however in practise this is rarely the case so one edge will be hotter than the other. On a road car with limited negative camber it is usually the outside edge which is hot, thus you might have 45/35/35 - in which case you should increase the tyre pressure to get the centre temp up to 40C for an even temperature gradient; however if the temp measures 45/45/35 you should drop the pressure to achieve 40C in the centre. I measure tyre temperatures with an infrared gun held around 25-50mm (1-2") from the surface.

Bob Rouleau

According to a bulletin from Toyo, 32 to 35 lbs HOT.

TAI2

With R888 on my 964, I started with 29/31 cold and ended up with 36/38 hot. Much depends on car set-up and driving style.

cobalt

I second that. Anything above 40PSI and they turn to grease and starting temps should be adjusted depending on ambient temps but this I found works best using 18's and same tire sizes.

race911

Which, I believe is what they carried over from the RA1 days. Which all of us moved passed once we got our own data. As I said above, I optimize at 38 hot. Worked perfectly fine on Saturday, from a damp, foggy morning through a dry line at 50F ambient in the afternoon. Excellent balance, if not lap times.

What I have heard though, and from someone attached to one of the "internationally known" engine/race prep shops around here, is that the Spec 911 guys are back down at 34 hot. But that's a ~2400 lb (w/ driver) car on 225/245. Similar weight on an SM with the 205s, none of the guys at the pointy end of the grid are that low. 38 recommended, don't go above 40.

Now I'll throw one out there--the old BFGs from the '90s. I don't think we ever went above 24 hot, "groove of doom" be damned!