Yep, I'm new... and there maybe many opinions, but here is a simple question, "What tire pressures are best for a standard Cayman 2.7 with 18 in wheels?" The standard 30/37? pumped up a bit, different F/R stagger to improve turn-in ??

Thanks.. D of D&D..

Scroll down to the bottom of this page to see a few threads dealing with your question. And then do a search for even more. And you guessed correctly about "many opinions".

D&D,

Like Santa Fe indicated there are many threads and many opinions, but here is mine.

Whether the car is a 2.7 vs. 3.4 does not much matter. It is more your driving ability (speed), external temperature, and type of track. The brand of tires also matters, as they seem to like different pressures.

Your cold pressure is really not what is important, it is the hot pressure (achieved while running on the track) as this is what controls how the tire reacts. Remember, the primary goal of managing the tire pressure is to keep the maximum amount of rubber on the track and this requires the tire not be either under or over inflated (you have seen the pictures of how the contact patch changes with pressure). Keeping the most possible rubber on the track also helps to keep the temperature of the tire more consistent across the contact patch and ensures you are getting the maximum traction available (effect of camber aside).

You also want to start with enough pressure in the front tires that they do not roll over on to the sidewalls under initial hard cornering.

So, where to start. The factory pressures are generally too high in the rear and too low in the front for use on the track.

PS2s - these seem to like 38 to 40 PSI hot at all four corners. Start with about 33 F and 35 R and bleed them down to 39 or so after each run through the day. You will probably be at about 30 to 31 cold all the way around when the car cools after your final run. I also think these can run lower pressures when new.

RE050A - these like a bit lower pressure (stiffer sidewall?) and seem to work best at about 36 to 37 or so hot (still experimenting). Start at about 32 F and 33 R cold and go from there. These get more “gummy” when hot and seem more consistent throughout the run than the PS2s. They are certainly more durable.

I do not yet have a pyrometer so I can not tell you what the surface temps are doing at the various pressures (one of the next investments).

I hope this helps.

Cheers,

D&D: I like Krokodil's answer for tracking. I think his general statement that the recommended pressures for the rear are too high, and those for the front are too low, also applies to spirited road driving. For that, I generally set the fronts at about 33-34 psi and the rears at about 35-36 psi. Bringing the front and rear pressures closer reduces the understeer Porsche apparently wants us experience.

Thanks for the add Jim. I agree with your advice.

Got it... better to have higher fronts and less hard rears vs OEM standards.. thanks for the good advice and starting points..
D

Perfect starting point. I did this TODAY.

I would add that if you are looking to optimize for ultimate performance as opposed to trying to extend tire life, get a pyrometer and learn how to use it.

The theory is that you are getting the best traction when your tire is heating up evenly across the contact patch, more or less.

I am trying to get even wear (tripling the number of days I get out of PS2s) by starting at the above pressures and using white shoe polish to mark the top edge and sidewall on each tire. After each session, check to see how far over on the edge of the tread you are getting wear and adjust pressure accordingly. Too much roll? Add air. At this point I use a pressure gauge to check pressure more out of curiosity than anything else. I try not to chase an "ideal" pressure. I look for the wear.

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2007 Speed Yellow Cayman GT 2.7 (retired)
2008 Guards Red Cayman GT 3.4
"Carpe Cayman"

Is anyone using TPMS? my tires got up to about 44 psi the last time I was at Thunderhill and they felt a bit skate'y. Then again the track temp was about 130 F so I should have bleed the cold pressure lower.

TPMS will give you relative tire pressures and is fine for the street to alert you that you are losing air.

The numbers it displays at the track are way off actual pressures, and it constantly warns me about tire failure that it thinks occurred when the tire cools down in between sessions. It will show differences in tire pressures that can't be confirmed by a hand gauge.

Yesterday was the first time that I ran my non-TPMS 18 inch wheels and it was really nice to not have warning lights and chimes saying "you blew a tire and are about to die" as I am entering a corner at 95mph.

Just my experience.

__________________

2007 Speed Yellow Cayman GT 2.7 (retired)
2008 Guards Red Cayman GT 3.4
"Carpe Cayman"

Properly used, a pyrometer will also extend tire life. That's been my experience having used one for years. Among the things learned w/the pyrometer is that starting at a lower cold pressure can result in the same hot pressure due to greater tire movement and heat buildup, but with more even and higher tread temps, greater grip and more even wear. I mark tire sidewalls for my DE students (and for myself) to check on tire roll, but more to graphically demonstrate how much (or how little) of the available tire tread is being used. I use liquid sidewalk chalk rather than shoe polish because it's water soluble and washs off easily. Regardless of where you start, remember that pressures will need to be adjusted during the day because of changes in ambient and track temps, track configuration, and other variables. I start my street tires at 32F-34R cold and after a day of adjusting at the track I end up the next morning w/different cold pressures in each tire.

__________________
Dan