HPDE Tire Pressure Help

[Phosita]

The suggested tire pressure (cold) for on-road driving for the Bridgeston Potenzas on my car says 37 psi front, 47 psi rear. However, I cannot find any suggested pressure information to drive them on the track at a HPDE event. Everyone suggests much lower pressures for both front and rear. However, I do not know how low to go. Any suggestions or information would be great.

[Loren]

:welcome:

You start with lower pressures at the track because the pressure will rise as the tire temperature rises.

You may have to adjust to what others with your same car are doing. Do not start below 32 PSI and remember to warm the tires before taking any high speed runs.

Best to take a few laps and see what the temps are then. Then adjust up or down depending on the cars handling. If you don't know how to do that let an instructor help you the first couple of times.

[jadatis]

Tire pressure advice is all about load on the tyre and speed you drive with.

I registerd to this forum to give you an answer, and I think,give usefull information.

Dont have a Porche, so wont introduce myself in a seperate topic.

Once got hold of the formula , the European tire-makers use for decades,and the American since 2006 for standard load and XL.

The pressures you write are for maximum load, and rear even maximum overload or shifted load R/L,For maximum speed of the car, so are even for on the road with only driver and a little load, much to high. This is only for the tire-maker, so he wont get a law sute when someone,goes to the edges of what is possible.

I must say that for tires with low aspect-ratio ( 235/40 ZR 18 92Y XL for instance the bold part) I have my doubts about the calculation of the maximum load the tire makers do, so there you better be on the extra save side.

If you first calculate the needed pressure for the weights you use when driving , and then fill it in another spreadsheet of mine, you will get the pressure you have to fill cold , to get a warm pressure that is right for the race.

Under here a link to my public map of Skydrive/hotmail. Click at the end of the line of the document or map you want to use on the I in a cirlcle. Then at the right barr the info appears about it. Click on Download, and after downloading open spreadsheets in Excel or compatible programm to work with it. In the browser wont work because it cant handle some things I used in them.r

You need the map "recalculating tyre-pressure" (7th map) and spreadsheet 1 from the bottom "pressurecalcution with temp" .

https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC%21128

If you cant figure it out yourselves, give me here the details needed, and I will do it for you as an example.

Greatings from Holland.

Peter

Edited September 7, 2011 by jadatis

[PAULSPEED]

I start out driving on the track with the pressure

2 psi lower on all four wheels.

After your first session you will see higher pressures

unless your tires are filled with nitrogen.

Drop to the 35 psi/45 psi for your next session.

Go to Radio Shack and buy a $20.00 surface temperature

gage. Measure the temperatures across. Try to get the same

across.

Fill up the tires before leaving the track.

Paul