Tire Pressure Question

[csj1]

We have run into a problem a couple times with gaining too much tire pressure by the end of the heat race. The car is still handling good but we know once we go to the main the lap counts go way up the car will fad with the elevated tire temps. Is it better to drop all of the tire pressures down by the same psi level or do you drop them by the same percentage. As an example on the percentage side if you have a right front at 30 and you drop it 10% you would start at 27. If the left rear was at 20 you would drop it to 18 to keep with the 10%. Thanks for the help. CJ

[RACEMAN]

Stick with actual number of pounds. If you use percentages it may lead you in a direction you don't wish to go. Think of it this way if you use percentages: 10% of 10 is 1 pound, 10% of 20 is 2 pounds. This happens all up and down the scale.

Using what I recommended before, I think it will be easier to track changes and performance.

If you can use tire bleed valves I'd go that direction. Once you understand them I think you can control the situation a bit better.

[84Dave]

Use a tire pyrometer and measure the temps in (3) places across all (4) tires immediately after every heat race. The temps, ideally, should be within about 10 degrees across the tires. And too much/too little camber in either front tire can/will show a heated tire on one side that can increase the pressure. The average of the temps in the RF & RR should be close to the same. The same is true of the LF & LR tires. An excessively high temp in the middle of the tire indicates too much tire pressure. And in our experience on our Pro-4, with a good handling chassis, the left side tires will show a temp average near 40 degrees LESS than the right side tires. And we always use a filter on the tire pressure hose to remove as much H2O/moisture as practical. Tires like air/N2 with as little moisture as practical. Oh....... with rear stagger & proper camber up front, the left side tires should show a slightly higher temp on the outside. The right side tires will show the slightly higher temp on the inside. -Dave-