Planet 9

BillL223 · #1 04-11-2009, 01:16 PM

I ran a set of R888s at NJMP and thought I'd report my findings. The tires are 245/40 x 18 and 275/35 x 18 on OEM Cayman S wheels. I have -2 degrees camber on the front and - 1.8 on the rear. After playing with pressures and collecting some pyrometer data, I ended up with 33 hot on the front and 36 hot on the rear. The tire temps were taken after a full cool down lap and back in the pits so they are lower then if taken immediately after a hot lap. Ambient temperature was about 55 degrees. Average on the fronts was 114 outside, 125 center, and 137 inside. Average on the rear was 124 outside, 131 center, and 130 inside. An alignment problem was discovered on the left rear so these temperatures may change. Does anyone else have any data to share?

**ValveTubeHead** · #2 04-11-2009, 01:23 PM

There's some thread chatter goings on over at Corner-Carvers. While not porsche specific, may be informative.
vth

**KS-CS** · #3 04-11-2009, 05:31 PM

Originally Posted by BillL223

. . . I have -2 degrees camber on the front and - 1.8 on the rear. After playing with pressures and collecting some pyrometer data, I ended up with 33 hot on the front and 36 hot on the rear. The tire temps were taken after a full cool down lap and back in the pits so they are lower then if taken immediately after a hot lap. Ambient temperature was about 55 degrees. Average on the fronts was 114 outside, 125 center, and 137 inside. Average on the rear was 124 outside, 131 center, and 130 inside. . .

That's an interesting finding on the fronts - to me it would imply that maybe that much front camber isn't necessarily a good thing, especially since the hot pressures weren't that high. It would be interesting to see some more data from someone who has closer to stock camber on the front. Any indication of uneven wear on the front tires?

BillL223 · #4 04-12-2009, 06:50 PM

I measured wear today. LF outside was .060" more then inside, RF was outside was .033" less then inside, LR outside was .010" less then inside but this is the tire that developed an alignment problem (too much toe in). RR had equal wear inside/outside. My conclusion is that on the heavily loaded outboard tires camber angle is not excessive.

**fondueski** · #5 04-12-2009, 07:54 PM

Did you have them shaved?

BillL223 · #6 04-13-2009, 07:38 AM

I did not have them shaved as I drive to the track with the tires on.

Jim Michaels · #7 04-13-2009, 11:29 AM

The Toyo website recommends hot pressures in the high-30s to low-40s. I thought I remembered Toyo initially recommending mid-30s hot, but the current Toyo recommendation is more consistent with the thread chatter mentioned above.

janderson · #8 04-13-2009, 05:07 PM

Bill
How do you know there was an alignment problem and what was the problem.
Jim A

BillL223 · #9 04-14-2009, 08:06 AM

During one session I noticed that I had the steering wheel angled to the right as I was going down the straight. PSM also disabled itself. Upon inspection I found extreme toe in on the LR. Did a quick and dirty toe change at the track. After returning home and getting some suggestions from the folks on Rennlist, who suggested that something moved on the camber, I found the LR camber eccentric bolt head at the inside position and also, without loosening the nut, was able to, move the eccentric with modest effort using a combo wrench. I believe that the camber eccentric bolt was not properly torqued, moved and changed the toe.

BillL223 · #10 06-04-2009, 05:55 PM

Since my original report, I have run two more track days, both "Advanced" days with 5 ea. 45 minute sessions. I found that 36H in front and 38H in rear became greasy as the session went on. There has been some discussion of running higher pressures and I tried 40H front and 42H rear. I could not feel any improvement. Yesterday I decided to go the other direction. I tried 32H front and 34H rear. The tires did not seem to go away at the end of the session. Pyrometer readings looked good. Tried 30H front and 32H rear. Pyrometer readings also looked good. My last session was a compromise, 31F and 33R. I'm thinking this pressure is where Toyo R888 on a Cayman need to be.

DaveD · #11 06-04-2009, 07:13 PM

Thanks for posting the info, Bill. I may as well add a brief bit of info myself.

'06 CS, -0.8 camber front, -1.5 rear, 245/40-18 & 275/40-18.

At summit with low 70's ambient I was running 36 front / 38 rear
probe style pyro gave front temps 182/179/184 L, 160/155/163 R (outer first).
I didn't take rear temp readings. FWIW, my cheap IR temp meter was within 5 degrees as long as I took readings in the shade.
Half a lap cool down, so actual temps would have been higher.

Also, looking at wear on the shoulder of the tire, I could see there was still room before I was hitting the edge of the tread area.

Based on all this, I was planning to go a bit lower pressure at my next event. Since the recommended temp range is 160-220, I'm thinking lower pressure will bring my temps up some. Your experience seems to confirm that. Also, I saw a posting from a boxster racer on rennlist that was running in the low 30's with good success.

Dave

FT · #12 06-04-2009, 09:10 PM

This whole R888 pressures threads across all the boards is quite interesting. There are couple Caymans in Potomac in my run group running on the high 30s pressures with stock suspension with really good results.

However, after trying several pressure sets, my car feels very skittish with high 30s. Finally, after 42-46 session on the current set, I have settled to using 34 front and 38.5 rear pressures with very good wear and excellent grip IMO, stock suspension with -0.95 front and -1.6 rear camber. No matter what Toyo says, I am sticking to these pressures

To me the most suprising about these tires have been their consistency as they wear down; at Summit I am still running within 1 second compared to when they were still fresh. I think I have 3-4 more days left of them and that will be close to 60 sessions on a single set; great value for me.

chuckb · #13 06-04-2009, 09:36 PM

what sort of lap times are you running?

FT · #14 06-04-2009, 09:58 PM

Ranges between a best of 1:29.8 to 1:31 (most consistently).

chuckb · #15 06-05-2009, 09:13 AM

That's honking! Thanks

FT · #16 06-06-2009, 08:31 AM

Not quite, average times overall; I'd like to be able to do 1:27-28 consistently; may be new shaved R888s may give me that, we'll see. But its tough to take some risks without a roll cage and other safety precautions.