Categories : Blog Posts
Your tires have air in them. For autocross, that air needs to be at the best possible pressure to support the weight of the car and use as much as possible of the tread surface to give you the best possible grip as you turn and twist around a course. So, where do you start?
With a look at the driver’s door pillar. That’s where you will find the sticker with the manufacturer’s recommended tire pressures. Those pressures are based on the weight of the car and the desire for a reasonably comfortable ride. They do not take into account the potential for high cornering loads that autocross puts on the tires. If you try an autocross with the standard tire pressures, you will very quickly start to see excessive wear on both the outer shoulder of the tire and, possibly, out onto the tire sidewall. This means that the tire is rolling over onto its outside edge and beyond under hard cornering.
To fix this, you need to stiffen up the tire by raising the air pressure. A rule of thumb(based on the experience of lots of autocrossers) starting point is to add two to three pounds of pressure to your tires. This will help to stiffen the tires and reduce the tendency to roll over on that outside edge. This is just a starting point. Each car/tire combination then needs to be adjusted to find the best working pressure.
Some visual aids can be a big help with this. Marking from near the edge of the tread out onto the sidewall with a piece of chalk or a shoe polish applicator can help you see just how close to(or beyond) the edge of the tread you are actually getting. If your wear is not reaching the edge of the tread, the tire pressure is just a bit too high and you can drop it by a small amount, do another run on the course, and check the wear, again. If you are still getting wear out beyond the edge of the tread, the tire pressure is still just a bit on the low side. Try adding about half a pound of pressure, run again and then check the wear, again. Once you find that pressure that lets you use all of the tread of the tire, then the trick is to keep it there.
As you run around an autocross course and put all that stress on your tires, you are generating heat in them. Try putting your hand on the tread of a tire before and after a run to see how the temperature changes. Adding heat will raise the air pressure in your tires and make them even stiffer. You will need a good air pressure gauge to see how much the pressure rises, with a bleeder valve to let you adjust them back down to your ideal pressure.
Again, these are just some basic pointers to help you get started. If there is someone else running a similar car, talk with them about the pressures they are running. But, always pay attention to your tires. Check the wear patterns. Check the temperature. Check the pressure. As you do these repeatedly, you will quickly learn the best pressure for your car/tire combination and how to keep it there.
Article written by Walter Phillips