Measuring tire temps at AX, What am I doing wrong? Options

[Joseph Mills]

At the last AX, after several runs, I went from 36# to 30# for the front tires (Hoosiers). At 32# and above, the inside was about 5 deg. hotter than the outside. Below 30# the outside started heating. At 30# they were about 117 deg. all the way across the tire. Good. And the car does not push.

The rear tires were about the same temps. However, even when I went as low as 26#, they are STILL about 6+ deg. hotter on the inside. And at 26# the car was starting to get a little loose, but easily controllable. Below are some things I've considered, but really, I don't know where to go from here.

My car does have 1/2 deg more neg camber in the back than the front....

It was a short AX - around 38 sec's with some straight ahead driving - which would tend to heat the inside tread....?

Maybe I need a faster/longer AX? Or can you only do proper readings on a skid pad or figure 8 only....?

Could the engine heat up the inside of the tires? Usually spend 5 -10 minutes with engine idling and slowly creeping up the line.....???

My "pyrometer" is very cheap, but seems to be very reliable with repeated readings.

Any ideas out there??? HELP! (IMG:style_emoticons/default/ph34r.gif)

[john rogers]

Tire temps seem to be a black art, almost. Here's what I have noticed over the years: many PCA 914 auto-x'ers run pressure too high, such as 34# or even more but get even temps across the tire. Many have gone much faster when they lowered pressures to the 26# range but get uneven temp readings, usually the outside is getting too hot. This temp increase can be from some tire roll-over and the fact it is gripping much more since the foot print is larger. To compensate more negative camber (varies as to which tire) must be used but since alignments are expensive they do not get done. You need a person to check the tire temps for you immediately after your run and if possible use a probe type pyrometer but any type is better than none. 914s can get some heat build up on the rears if you are sitting in linefor extended periods and this can raise the rear tire pressures a pound or two which can affect the way the car handles from one run to the next. A very accurate tire pressure gauge is a must so you will know exactly what the tires are doing. As Chris said, a 5 degree difference is fine but if you get over that then tunning is needed.