Just did a couple of track days at Lime Rock. I started the day with 34psi front and 42psi rear. Measured the tire temp multiple times during the day. Found that the outside/middle/inside temp's are all linear even when the temps are not the same for different tires and between inside edge and outside edge of the same tire.

I pushed the car rather hard so the hot psi went way over 50 front and back.

I've heard people recommending lower hot pressures. The question is should I go with the pyrometer or should I go with the lower pressures which will surely decrease the temp on the middle and make the readings nonlinear?

Thanks.

 

I believe that you should stick with what gives you the similar readings across the tire. That is telling you that the tire's contact patch is flat to the road and you are using the tire's surface optimally.

 

Where was you car feeling better?

 

Didn't the car start to feel slippery @ 50 psi+?

 

ypshan:

What camber are you running?

 

Beware of taking pyrometer readings unless you take them
almost immediately after the last turn. Tire temps will
be at their most telling then, but a short distance of non-racing,
non-cornering will allow the tires to cool, but more importantly
allow the temperature *difference* across the tire to dissipate.
Some race cars actually install temp sensors in the fenders to
see the tire temps at three or more places at real time to
get this 'fresh' info.
How is you tire wear? Are you looking for even wear over time,
or for maximum lap times? These may be conflicting...
Joe

 

My camber are:
-0.14 Front
-1.5 Rear

I turned in the best time (1:08) when the tires were hotest so I didn't feel they got slippery. I have Conti Sports Contact 2 by the way. They are not very sticky. I'd say less traction than P-zero. And they squealed like a pig.

When I looked at the wear marks, they seem fine with the high hot psi readings. I did not roll into the sidewalls nor just wore out the middle. My purpose is faster lap time instead of even wear.

I have the needle type pyrometer that I need to stick deep into the tires. The temp inside doesn't seem to go down as fast as the surface. I also try to take the temp as soon as I pit. I could get 25 degrees difference between the inside and outside.

 

Independent of tire temps/pressures, you are probably
experiencing a lot of understeer, if you turn of PSM.
If you want to corner faster, try -1.5 degrees of camber
in the front too.

 

It's funny that I got a lot less understeer than I expected. The car seems to want to drift on all 4 wheels. I thought I might not be driving aggressively enough so I asked a club racer to push it hard at Pococo. He indicated the same that the car feels neutral with slight understeer.

Also -0.15 seems to be as far as the Porsche spec allows in the dealership. It's the max value on the compute print out.

 

Increasing the camber will get the inside of the tire hotter quicker but will wear quicker as well. The extreme of this example is the cup cars that are now running > 5* neg camber and slightly inflating the tires (higher than the usual 6# less than cold PSI recommendations) so that not only do the insides get really hot quick, but the middle gets hotter, too. This results in very sticky tires, spring effect from the sidewall stored energy without significant loss of tire patch, and consequently, they go through tires quicker than my daughter goes through diapers.

The trouble with the pyro readings is you really can't afford a cool down lap for good readings and it is true the ideal temp range is happening during the turn and not once a straight is completed and then jump out of the car and measure. I would say though that you can still get a good idea about comparing the three zones, know the hot pressure recs of your individual tire brand, and it is OK to have 20-25* spread between the three zones of each tread.

IMHO, if you really want to get the lap times down, get slicks and then concentrate on your skill and the fast line.