Durometers can be a very effective tool
for selecting the best tires from a new stack as well as helping to decide when
your used set needs replacement.
Durometers measure the relative hardness of the rubber on your racing tires.
In order to get the most accurate results you need to follow a standard routine.
You must apply equal pressure to the durometer each time you take a reading. If
you press the durometer down very hard one time and then very soft the next your
results will vary due to the uneven hand pressure.
You must also take a measurement quickly and be consistent when taking
readings. If you place the durometer on your race tire and leave it in the same
spot for several seconds the rubber will deform, giving you a false reading. The
rubber conforming around the durometer-testing probe will create the false
For the best results you should take your durometer readings as quickly as
possible. Simply place the durometer on the tire surface with the footpad at a
slight angle. Lightly roll the footpad until it is flat on the tire, take your
reading and record the measurement.
For accurate results you must also consider the temperature of the tire. Hot
tires will be softer than cool tires. If you are looking for the softest tires
in a stack then you need to take care that you take durometer readings in equal
environmental conditions. For example, if you take a reading on a tire that is
in the hot sun your durometer reading will be softer than an equal compound tire
that is in the shade. The side of a tire facing direct sunlight will generally
read softer than the side facing the shade. The temperature difference results
in a durometer reading difference.
Temperature can affect the tires that are on your car. Tires that have heat
from a hot lap session will give you a softer durometer reading than tires that
have not yet been run. If you check the tires with a pyrometer you can insure
that the tires are the same temperatures to insure more accurate results.
On tires that have been run be sure to prep the tire surface for a proper
durometer reading. You should take a small scraper and remove any loose
rubber from the tire surface. Removing the loose rubber requires little
effort on hot tires. Cold tires require a little elbow grease to get down to
the true tire surface.
When race tires are hot they are very sticky. Riding around the track
on a cool down lap and driving through the pits allows the hot tires to
pick up the loose bits of rubber that are lying on the track surface.
The loose rubber adheres unevenly to the tire surface causing false
readings. The loose rubber must be removed with a scraper to allow the
durometer footpad to sit flat on the actual tire contact patch. You must
remove the loose rubber to get accurate durometer results. If you are
checking your tire wear with a tread depth gauge you need to remove the
loose rubber as well.
Remember, durometer hardness is only part of the tire equation. Tire
compound, chemical composition, tire tread gauge, sidewall design, heat
cycles and tire wear are all factors that affect the performance of your
tires. Considering all the variables and using your durometer
measurements will help you to select the right tire for the right
conditions. Proper use of the durometer will allow you to track the
condition of tires, giving you the chance to replace them before the
tires get too hard for competition.