| TIRE BASICS 1 |
| "The tires on your car have more effect on its handling than any other component" |
| Herb Adams - 'Chassis Engineering' - pg.1 |
| Tires are unquestionably the single most important component of vehicle performance. The reason being is the simple fact that they're the only part of the car that comes in contact with the road surface. I read a quote from a guy who had an excellent autocross website a few years back, and he was discussing tires. Basically, he said in regard to setup that if you're on the wrong tires you're not going to win. |
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| The first day I ever took my car to the race track, my class instructor showed me a diagram like the one above and asked me which of the two lines was the fastest. The correct answer is completely counter-intuitive to the average person, but the inside line, despite being shortest distance, is the slower line. The outside line is faster because it requires less steering input, and hence the tires scrub off less speed. The guy who steers the least is going to win. |
| This is helpful to know when you're out there running laps; the key to being fast is taking the line that requires the least amount of steering. |
| Increased steering angles limit our ability to put power down, the more steering, the greater the lateral loading of the tires |
| and the greater the lateral loads, the less available traction remains for straight line acceleration. Understanding lateral and longitudinal loading of tires is elemental to success be you a tuner, driver, or both. So let's dig in.... |
| TIRE TRACTION and VERTICAL LOAD |
| The two most basic concepts when dealing with tires are understanding tire load and tire grip, more specifically, 'Vertical Load' and 'Traction.' |
| "Vertical Load' - the input for tire performance is the vertical load, or weight, on the tire. 'Traction' - the output of a tire from a handling standpoint is its traction, or how well it "sticks" to the ground." |
| Herb Adams - Chassis Engineering - pg.1 |
| Herb Adams elaborates further on tires by defining tire behavior in terms of input and output behavior. Basically the tire input is the amount of vertical loading placed on the tires, while the output, is the amount of traction the tires have as a result of the loading on them. |
| Tires are tricky to understand, as with most anything that relates to tuning. This is because performance and results are always on a curved graph. Too much of anything tuning is bad, and too little of the same is, well...bad as well. What this means is that tires will lack grip in one of two ways: |
| 1- Not enough weight or loading of the tires. 2- Too much weight or overloading of the tires. |
| Tire loading becomes more complicated based upon the fact that as soon as the car gets set in motion the loads change. Tires are loaded in four basic ways: |
| 1- Static Load - This is the load on the tires from the vehicle's weight when at rest. 2- Lateral Load - The transfer of weight from the inside tires to outside tires during cornering. 3- Longitudinal Load (dive) - Weight transfer to front tires under braking. 4- Longitudinal Load (squat) - Weight transfer to rear tires under acceleration. |
| Basically, the more you load the tires, the more grip you get, but to a limited extent (because it's on a curve, right?). Once the weight on the tires exceeds its tractive capacity (co-efficient of friction) the tire loses its grip and breaks loose. To better understand the concept, we need to understand the tire performance curve associated with any tire, from a street tire to race tire. |
| In order to elaborate further, we can assign some values to the numbers on the chart (below): |
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| Based upon the information above, we can infer the following: |
| "By looking at tire cornering efficiency, you can easily see that you get the most cornering power as a percentage of the vertical load when the vertical loads are lower. A tire's cornering efficiency reduces quickly when asked to support more and more weight......Understanding this aspect of a tire's performance is necessary to analyze the more complex conditions that a car experiences during actual driving conditions." |
| Herb Adams, 'Chassis Engineering' - pg.2 |
| The amount of traction available from any given tire dependent on how much weight is on it. As weight (load) is increased the traction also increases. The important thing that must be recognized, however, is that the increase in traction becomes less and less as the load is increased. Hence, although there's an increase in total tire traction, its cornering efficiency decreases. |