Design and Build your own car

The grip provided by a tire is also based on the coefficient of friction (Cf) of the rubber compound and the tire’s construction (Radial/bias). This coefficient indicates the lateral grip the tire is capable of providing for a given weight being placed on it. A Cf of 1.0 means it is capable of providing 1 lb of lateral grip for 1 lb of vertical load on it.

Racing slicks (tires with no tread) are very high Cf tires, in the range of 1.0 or more. Street (treaded) radials, on the other hand, rarely even approach a 1.0 Cf. If you were to place 500 lbs weight onto a tire with a Cf of 1.0, you could expect 500 lbs (actually a little less) of lateral grip. Without aerodynamic aids to add to apply further weight to the tire, the vehicle could almost achieve a 1G turn.

Wheels

The wheel is what the tire mounts on and each type of wheel has its own particular characteristics depending on its width, diameter and construction materials.

The primary types of wheels used on cars are alloy and steel.

Alloy wheels can be constructed to very minimal weights, as alloying materials such as aluminum and magnesium can be used. They are also generally much more expensive than their steel counterparts, but they also lack the dent resistance of steel wheels. An alloy wheel, when struck by a curb will sometimes shatter and crack. Nonetheless, for most motorsports series and street vehicles, alloys are the choice.

Steel wheels can also be constructed to very low weights and their cost is quite a bit less than the alloys, due mostly to lower cost construction. Steel wheels are deformable when struck, and will usually allow air to leak out of the tire, as opposed to shattering. NASCAR and the general stock car scene use steel wheels due to the extreme forces encountered.

Wheels, aside from their width and diameter, have an important design characteristic called “Offset”.

In the wheel/tire cutaway diagram WH1 below, the sample wheel shows a red line that represents the mounting face for the wheel—the face with the lug holes that we bolt onto the hub of the vehicle.

The yellow dotted line represents centerline of the wheel and “Zero offset” from the centerline. If we move the mounting face toward the vehicle, as show on the left in the diagram, we create “Negative Offset”. If we move the mounting face away from the vehicle, as shown on the right in the diagram, we would create “Positive Offset”

Offset is important in relation to the design of the upright/knuckle, as it determines scrub radius (see more info below).

Brakes

It goes without saying that while the gas pedal on your car is the preferred pedal to push, the brakes are of vital importance as well.