A tire is a tubular corded carcass covered with rubber or synthetic rubber, which is mounted on a wheel and inflated to provide traction for moving a vehicle and for assisting the brakes in stopping it. Today`s tires, when properly inflated, will absorb bumps on a road’s surface and give a safe, comfortable ride, while providing a reassuring grip on the road at all speeds.
TIRE TYPES AND MATERIALS
There are two basic types of tire: the tubeless tire for passenger cars and light-duty trucks; and those requiring inner tubes for medium and heavy-duty trucks. Government regulations require that every passenger tire be stamped either “tubeless” or “tube-type,” but more than 90% of the passenger cars are tubeless. “Belted” would indicate that a tire has extra strength in its construction. In addition, if the tire were a radial, it would be designated as such – a necessary precaution because radials should not be mixed with other tire types except when the radials are used as the pair on the rear axle.
Bias Ply Tires
There are three general methods of arranging or laying down the tire plies. They may be laid down “on the bias,” “on the bias and belted,” or “radially.”
The standard, and least expensive, tire is a bias ply. In this type of ply, the cord strips are arranged diagonally (i.e., at a bias) to the center line of the tread and alternate plies are reversed to cross at a 30 or 40 degree angle. The result is a uniformly firm body, which will wear satisfactorily at moderate speeds, with sidewalls that can stand curb bruises. In fast driving or hard turning, however, the tread elements squirm together and spring apart, producing heat that weakens the tires.
Bias Belted Tires
Bias Belted Tires are the same as Bias Ply Tires except that they have additional layers or cords – or “belts” – circling the tire beneath the tread. This adds some strength to the tires.
Radial Ply Tires
Radial Ply Tires (or just “Radials”) have ply cords which run across the center line of the tread and around the tire. The two sets of belts are at right angles to each other. Most belts are made of steel wire (“Steel Belted Radial”), but others are made of ployester or other substances. Most tires today are radial tires.
Drag Racing Tires (“Slicks”)
Drag Racing Tires (or more commonly called “Slicks”) are a special type of tire used in drag racing where maximum acceleration in a straight line is essential. They are made of a soft compound of rubber, which affords better traction, but they tend to wear out very quickly (around 100 miles). The sidewalls of slicks are designed for straight-line performance, rather than cornering. In fact, as they are perfectly smooth with no tread pattern, they provide almost no traction in turns and thus are not street legal. Slicks are made of a soft compound, which are designed to give way to any stresses. The are also known as “Wrinklewalls”, as they actually deform when you stomp on the accelerator. The power from the engine goes through the transmission and rear-end components, through the axles, and is applied to the rear tires. The slicks try to rotate, but are resisted by the friction of the ground. The tire ends up spinning faster at the center of the wheel than at the outer edge near the ground, which results in the tire wrinkling around a portion of the bottom of the tire. The physics behind the wrinkle is this: when the slick wrinkles, the tire creates a larger contact patch with the ground, or area where the surface of the tire and the ground are in contact. Looking at it from the ground’s perspective, you would see the original contact patch, and then when power is applied, you hold onto what you had, and the tire forces more of itself down onto the ground on the front. In simple terms, the tire does flatten out, creating a larger contact patch, and thus better traction. What if that first application of power is too much for the ground’s friction to hold onto, though? Well, that’s simple too: the tires spin, and you lose.
The soft compound of the tire is composed of not just a special formula of rubber, but of some traction-aiding chemicals as well. To activate these chemicals, you have to heat the tires up. The usual method is a burnout. Heating the slicks releases some of the chemicals, and the tires become sticky to the touch. This sure doesn’t make them last any longer, but consistent traction is a key to winning races. Not heating the tires is going to lead to traction deficiency, but over-heating the tires can do the same. If too many of the chemicals are released and get too hot, they can actually make the tire slippery.
UPGRADING YOUR TIRES
Standard tires, bias or radial belted, are compounded to provide the best overall combination of tread mileage, traction in both wet and dry conditions, durability in hot and cold driving, stability in turns, resistance to road hazards, etc. Specialty tires will trade one or more of these attributes for improvements in specific areas. Drag slicks with no tread pattern obviously would have no traction in wet conditions, and terrible handling in any kind of driving other than a straight line, but do provide optimum traction on a clean dry surface. DOT approved drag race tires provide some limited driving capability, (albeit very marginal) while maintaining good traction on clean roads. BF Goodrich has introduced a radial tire with improved straight line traction, and the normal good handling of the radial design. In general, long mileage tires are generally weak in straight line traction. If you plan to use conventional tires for drag racing, look for a relatively soft tread compound, a minimum of tread openings, a wide and flat tread, and a larger diameter. Increasing tire diameter by one inch will always increase traction more than increasing the tread width by one inch.
Increasing the Size of the Tires
It is generally accepted that larger diameter tires are preferred for greater performance. This is generally due to two reasons:
- They have a larger contact patch. For the same tire width, air pressure, tire construction, and material, a larger diameter tire will have more rubber on the road because the patch is longer from front to back.
- They apply the force more parallel to the ground. The force is applied at a tangent to the surface of the wheel. With a larger tire, more of the force will be available to move the car forward.
However, larger diameter tires do have some drawbacks as well. Some of these include:
- Larger diameter tires tend to be heavier. The tire is part of your rotated mass and part of the unsprung weight so heavier is bad.
- They have more inertia because the rotating mass is further from the center of the tire. Thus, more energy is wasted just to overcome the tires’ increased inertia.
- They require more room in the wheel well which may mean having to “jack” the car up, which is bad for weight transfer.