Finding the correct tyre pressure for your (race) car
This is a reply from Bill Babcock to a question
about what tyre pressures other people are using for a certain
race car tyre
24 pounds, and if you use that you'll be three seconds a lap
slower than you
could be. That's not the answer you want. The long diatribe
below is closer to the
It's important to develop your own tire pressure settings since
pressure depends on your car setup. Tires are springs, so your
weighting, brake bias, nature of the track, suspension setup
and how skinny
you are all play a big part.
Yokohama A008s are radial tires with low sidewalls and overhang,
camber is very important too. You'll need 2.5 to 3 degrees of
again, your mileage will vary--best way to set that up is with
a skid pad).
If you start with 20 pounds cold you'll have enough pressure
to keep the
tire firmly on the rim. Run a couple of laps and do tire temperatures.
need a needle pyrometer to do this properly. Push the needle
surface of the tire at an angle, deep enough to just bury the
about 1 inch inside from each edge and the center. Have a helper
do it all
very quickly after you've stopped in the hot pits. Read the tire
and the rim temperature at the same time.
The center of the tire should be about the same temperature
as the inside.
Depending on how tight the track is you may find the outer edge
is quite a
bit colder. This can be too much camber, but it's likely also
running down the straight (that's why a skid pad is better).
If the center
of the tire is substantially colder than the inside edge, add
a pound and
try again. Lather, rinse, repeat until the center is within a
few degrees of
the inner edge. By this time you will have built up some rubber
on the tires. If you have a smooth surface from edge to edge
camber is great. If there is nothing on the outside edge and
lots on the
inside then consider reducing camber a little. Look also at the
blocks. If they show scrubbing either inwardly or outwardly then
might be excessive either way. I like zero toe, but that's me.
If you can find a place to use as a skid pad (a place you can
run in a
100-200 foot or so circle for ten or more laps at a time without
arrested) then you can set your camber and tire pressures exactly.
On a skid
pad you set camber until your temperatures on the inside and
outside are the
same, and tire pressure so the center is the same as both edges.
After racing or at the end of your test and tune day put the
car on jack
stands and let it cool overnight. Record the tire temperatures
morning (anywhere) and the pressure for each tire. That's your
inflation temperature as long as the tire temperature is close
morning temp. If it's a lot colder or hotter you'll have to guess
bit, but keep it in proportion. What you find generally is that
side tires take a little more pressure.
Most people run too high a pressure. After some study you can
look at the
cars in the pits and see it. They have a hot band in the center
front tires. I find it hard to go from too high a pressure to
pressure. It just seems to make the measurements less sensitive.
If I wind
up with a center temperature that's even slightly hotter than
the edges I
find it necessary to reduce the pressure by a two pounds and
start over. One
pound seems to have no effect going downwards, where a half pound
substantial effect going up.