What's the ideal tire pressures for front and rear? I have 19" Bridgestone RE050A's and front and rear says not to inflate more than 40psi. Should I set all 4 at the max 40psi?

 

Go about 33 front and 37 rear from cold.
monitor your tpms and you'll creep up 2-3 when hot.
I'll be adjusting mine this weekend to be 33a and 36 hot and see how that goes for a week ....

 

Start with the factory recommended pressures and adjust to your preference. Fronts should be lower than the rear.

 

+1 , cold should be at 68 degrees F just to clarify.

Early on I thought cold' meant temp when car has not been driven ( overnight, etc. )...until a very wise member taught me

 

I think it does mean after they've sat for awhile (i.e. overnight) and at ambient temps of 68 degrees and at Sea Level. Altitude and Ambient Temp differences do change your pressures slightly. Once you drive on them they warm up and change your reference point.

Here's an interesting thread covering this very topic.

http://forums.rennlist.com/rennforum...-pressure.html

 

36 front, 44 rear

 

If it's cold enough that the garage doesn't reach 68 degrees, what then?

 

My rears say max 40psi?!?!

 

Let's see. If you're not driving it, leave it alone. If you're taking it out, adjust it then... where it's warmer.

 

I believe, if I recall correctly, that there's a chart in the manual where it shows you to adjust accordingly how much psi to add or subtract -if the 'cold' adjustment temp is higher you will have to add the*increment shown on the chart and if the adjustment temp is lower you will have to subtract,etc.

 

At 68 degrees on cold tires I run 33/37 on my mpss tires.

 

Start here; I did with my previous '08 C2S. Then play around and see where you like it best. Cold, I ended up at 37 rear / 33 front for daily driving on the roads and highways where I live.

 

I have RE050s on my GTS. I set mine at 34 and 37.

 

There's a more detailed examination of the issue floating around, but I can't remember whether I posted it here or on Rennlist. I agree with Dan (Edgy) on that thread by the way. We just went into more detail with instrumentation.

Another race driver helped me evaluate optimum pressures for the 997.2 wearing Michelin Pilot Super Sports. The criteria on track are temperatures in the optimum range for the tread compound and distributed across the width of the tire as the manufacturer planned. We worked toward that goal and after a long day, we arrived at a three-pound differential front to rear, using 34/37 for public roads. A track setting has to take into account driver preferences and variations between compounds across tire models, and it's too late at night to get into the details. The other report is fairly easy to find. It would have been around October 2011 I believe.

That differential is considerably less than the six pounds Porsche specifies but it wasn't really arguable looking at the data. Someone reported that the latest owners manual for the 997 GTS used those same numbers. We speculate in that other thread, but it turns out Porsche has answered us, so we don't need to guess why they originally published six-pound differentials for the 997.

The latest placards reflect two factors, not just light load vs full load. They now distinguish high-speed use and normal use as well. Basically, a Euro-Autobahn spec and a USA spec that includes our track days since the dividing line is 160 mph. I don't know of a DE track with straights long enough for a Carrera to reach 160. Maybe a GT2, but I'd be surprised. You need Autobahns to worry about the high-speed spec.

Now in current models we have a spec for Euro/light load; Euro/full load; USA/light load; and USA/full load.

The spec for USA/light load has a three-pound differential, just as we measured after a lot of track laps. That published value is for my 991 of course. They probably won't bother to go back and publish USA/light load numbers for the 997, but for what it's worth that is the differential we established in a long careful day.

All the pressures I'm talking about are 'cold' which means 68F as Hella says above. Leave them alone as the pressures change with work and ambient temp changes. They are supposed to change. We design for that.

However -- and take serious note of this -- with fully loaded cars, as if you went on vacation with luggage and kids in the proto-seats in back, the published differential is even more extreme. It is nine pounds now. That suggests that in the 997 fully loaded, we want to use the original spec pressures. I had to turn in my owners manual. Was that 36/44 or 38/44? Whichever you see on the plate. Use that when you're running fully loaded and don't fiddle with it. They have good engineers at Zuffenhausen.

Gary