My 2007 Cayman S is recommended to be 32 psi front and 37 psi rear!! Strange?

 

I have a '07 CS and it says 30F/37R on the door jamb

 

I took mine in for an oil change and the mechanic recommended 30F/35R. With X73 and 20" Goodyears it rides really smooth.

 

I'm really not sure why the tire pressure recommendations changed so much over the years? I just wonder with the Cayman R being the most performance oriented model if they found that the 31/31 tire pressure settings were optimal for performance?

 

Maybe it's model specific. Really, "recommended" tire pressure is based on specific tires. Normally you want them to be in the 30-40 range to prevent uneven wear associated with over and under inflation. Other than that its preference on what kind of ride quality, handling, and over/under steer balance you like. It's possible some of the older models were oversteer heavy and it was better to have higher pressure on the rears for reduced grip and lower in the front for increased grip. Normally it's better to reduce front pressure so you get more grip and reduce normal understeer, but it varies by model.

 

This is really interesting to me because of a recent experience of new tires (same size different make) on a non-P car. It turned out that the recommended pressure on the sticker was too low. The rough explanation was that "new" 51 lb max tires have different properties form 44lb max tires of old. But then I've since read that maybe the max pressures are somewhat arbitrary.

So now I am thinking to start with the sticker pressure as "recommended" (which is what they say anyway) and go up from there. The trouble is to find a good way to decide on what the right pressure is. Feel and handling seem less than exact, and waiting for uneven wear seems dumb.

 

This might be a dumb question. Recommended tire pressure displayed on the door post is 33 psi but TPMS shows 30 front and 38 rear and difference is 0 on all four tires. I have 20" wheels on my 2015 CS.

Can anyone explain why? Or is my TPMS malfunctioning?

 

Forget the door post. That is the MAXIMUM recommended pressure. Ignore that. Read your manual .Porsche iManual | 2013 - Standard is 33/33. That is for driving all day at 165 (like on the autobahn). Comfort is 30/30

Your TPMS numbers are weird. Remember Cold means 68 and the differences do account for temp. So if its is 90 degrees, out BEFORE you start driving, that for comfort tires would be at around 32.

 

I was at Tech Tactics Easton a few years ago and asked that question. One of the engineers replied it was due to the different suspension settings, this was in going from the 987.1 to the 987.2.

 

Porsche went to an awful lot of effort to design the original Boxster with mid-engine near-perfect 50/50 weight distribution and low polar moment of inertial for optimum performance and handling... and then specced out suspension and tires to make it understeer horribly in every condition. Spec tire pressures are a symptom of that.

The best way to test tire pressures is on a skidpad with telemetry. I found the factory recommended rear pressure for my 986S was pretty close to optimal, but the front was way off; like 10lbs off. The 987.1 (Boxster & Cayman) recommended pressures are almost identical to 986 recommended pressures. 987.2 recommended (cold) pressures result in almost perfect optimal hot pressures, though. The spring rates between 987.1 and 987.2 are so similar that I don't buy the "suspension settings" answer for such drastic pressure changes. I suspect this was simply coincident with a philosophical change at Stuttgart that let the engineers finally ditch the understeer that plagued earlier cars, and that putting out more performance-minded tire pressures is part of that. My 987.2S at factory alignment specs has oversteer, not understeer.

 

With all our mixed wheel/tyre combos, it would help if we had a shot of this sticker by different years/models.
During my night car wash just now - I took a pic for your reference.

Btw it was the first time I noticed Porsche had numbered their stickers with a part number too!

2009/2010 2.9 Cayman.

 

Mine's a UK 2011 and the sticker is the same... Just for your reference too!

With all our mixed wheel/tyre combos, it would help if we had a shot of this sticker by different years/models.
During my night car wash just now - I took a pic for your reference.

Btw it was the first time I noticed Porsche had numbered their stickers with a part number too!

2009/2010 2.9 Cayman.
View attachment 61134

 

Maybe it's me but this sure is confusing. In my case, my 2008 came from the factory with 17" tires so the door jamb label is for those. The original buyer, I bought it when it was 1 year old, had 19 inch wheels mounted at purchase and that's what was on the car when it became mine. The service manager told me the 19 inch tire pressure for my 2008 should be set at 32 front and 36 rear which I've been doing for the past 6 1/2 years. I'm a real stickler for accurate tire pressures and at this point I have no freaken idea if those numbers are even close to the ideal pressure setting or maximum pressure setting or just a recommended pressure setting but feel free to run just about whatever you feel like. Other posters with 987.1 and 19s seem to use 32 and 37 and yet others use something else. The change in suspension from year to year, I understand them doing so, also seems a little weird as it relates to tire pressures. How does suspension tweaking but using the same tires and wheels justify changing air pressures? None of this makes a lot of sense to me and it's starting to sound like mumbo, jumbo. Is there an expert in the house? Maybe the Tire Rack guy can way in. :gossip:

 

How does suspension tweaking but using the same tires and wheels justify changing air pressures?

The tires are a fundamental and very important part of the suspension. The sidewall of the tire has a "spring rate" just like the actual springs do, and the spring rates of the sidewalls work with the spring rates of the coil springs to affect the handling of the car. But the tire's spring rate is variable and directly correlates with inflation pressure. Also, changes in alignment settings affect the optimal inflation pressure.

Once you start recognizing the tires as an integral part of the suspension, it's not hard to see that the "optimal" inflation pressure is affected by many other variables.

 

So I posed this question to our local PCA president (he is heavy into autocross and road course racing) and this is his response "They changed the tire pressures to eliminate the understeer which they have in all their cars for the average driver. Same size and brand of tires."

I also asked him what he recommends for autocross and he replied "The Porsche Sport Driving School says for an autocross with OEM tires, to raise the rear pressures by 2lbs PSI to help eliminate rolling over on the rims and to raise the front pressures to the OEM rear pressures or even 2 lbs higher so they are balanced at 2lbs over the recommended rear pressures."