Before going into other aspects of the car I still feel that not enough has been said about the common tire.
This next discussion will guide us very briefly over how a car's tire pressure and suspension is optimized for peak grip through reading the tire. I will end with a brief overview of radial vs bias ply tires.
The main goal of a car's suspension and tire pressure in a racing application is to keep as much of the tire on the road as possible. Whenever your tire is crooked, you lose traction and thus don't go as fast.
If a tire's pressure is to high, then the tire will not evenly distribute the load across the footprint of the tire (the oval shaped contact patch). Thus stressing the rubber on the inside more then the outside. Proof of this can be seen after driving any car numerous miles with over inflated tires, the center portion will be worn away while there will still be plenty of tread left on the outside.
With an under inflated tire the outside of the footprint gets over stressed and thus the outside of the tire wears more.
There are a few ways to see whether a tire pressure is set to high or to low.
The easiest way is to look at the tread and see how much of it is left. Or if you have slicks, look for a non consistent surface if you see the tire has started balling up like washed fleece, then your tire is being overworked in that spot. A harder but much more instant and accurate method is to record the temperature of your tire during use with infra red sensors while you drive. If you can't do that the next best thing is to probe them with thermocouples (digital thermometers) after driving. If that is still out of your league, a hand held infra red temperature gun will suffice.
The temperatures of the tires tell a tremendous amount of information about how much grip the car is getting. A nice even temperature across the width of the tire means that your suspension and tire pressure is close to set up (all that is left after that is working out the under/over steer, turn in response, ride height, corner weights, aero settings, etc etc ;) haha).
Now, how suspension ties into tire wear and temperature.
It is goal of whoever is designing suspension geometry to try and keep as much of the tire on the ground as possible. This is an intricate process involving a few common styles of suspension geometry and their near infinite variations as well as various types of anti roll mechanisms. I'll save more information on this in other articles.
If either side of the tire are warmer or more worn, that means your tire is probably leaning to much on that side (known as camber). The other possibility is that your tire was a dud and came out of the mold badly (which surprisingly enough happens more then you would expect, I have seen standard sets of stock car tires vary in circumference by as much as 2 inches!).
Until the day we see full actively adjustable suspension geometry, there will never be a perfect set up. For example if a car is set up where the tires are perfectly upright with 0 degrees of camber. It's ideal situation would be going in a straight line i.e. going down a highway or drag strip. However if you throw a few corners in the mix the side of the outside of the tire (relative to the corner) will get a higher load then the inside (assuming little or no camber gain... which again I will discuss in another article). Point being, there is no ideal setup, even f1 cars adjust their suspension depending on the track they are racing on, or even for how warm/cold it is.
Now to finish up this brief interview on tires.
Bias ply vs Radial ply tires, what are they and how do they differ?
Put simply a bias ply tire is a tire wherein the cord that strengthens the tire wraps around from one sidewall through the base to the other sidewall (see picture below). Many consider this type of tire old technology, which it is, but it is still useful in certain applications and still holds a couple advantages over the much more popular radial tire.
A radial tire, is a tire which uses different base and sidewall materials and construction. The main goal of the radial is to reduce how much the tire rolls over itself. It does this by incorporating materials such as steel belts or layers of kevlar.
This means that radial tires will generally have a flatter bottom, meaning a more distributed load and therefore more traction. In a corner it's construction also resists rolling/lifting of the tire. The flatter bottom also means that there is less rolling resistance which leads to better fuel economy.
Overall Radial tires are superior to bias ply tires. However the couple ways in which bias ply tires are better are as follows.
They are generally lighter, less mass in your tire means less inertia. And a few pounds of tire weight means a lot more then a few pounds of chassis weight. I'll discuss sprung and sprung mass as well as drive line inertia in other articles.
Although bias ply will never produce as much traction as radials, they are still easier to race with. As the tire rolls over itself it slowly loses traction, this slow loss of traction can be felt and it's much easier to ride along the outside of that traction circle when you can feel your car starting to slip. When Radials slip, it's a much more sudden loss of control. It is my belief that any inexperienced driver if put in a race car would perform much better with bias ply tires for this reason alone.
And there you have it, a brief introduction into tires! Now I will feel comfortable with delving into other areas of discussion.
What do you want to learn about next?
Sensors and data aquisition
Or suggest your own topic!