A fact often overlooked by newbies and some ‘experts’ to the RC world is the importance of and science behind tires in the performance of your vehicle. Sure, it’s fun to do donuts endlessly in the driveway, but if you really want to go anywhere fast, your tires will have a big impact on how you get there.
The only part of your car touching the track most of the time are the tires. Think about how tiny an area of the tire actually touches the ground is. Vehicles under 1/8 scale may not even have 2 square inches of contact patch! You have to maximize your use of this contact patch as much as possible, sometimes it can make a bigger difference in track times than any other single modification.
Why is contact patch important you might ask? Since it’s the only part of your car touching the ground, it’s the only place where force can be transferred from the ?track to the vehicle. The amount of force that can be transmitted determines how fast a certain tire can accelerate a given vehicle in a given direction. A tire with a lot of grip always = faster. Unless you’re going for style points, a la drifting, you want as much grip as possible.The force a tire can generate is comprised of several factors which may help you decide what tire to run for a certain track condition. Rubber tires generate this force in three different ways, adhesion, deformation, and wear.
Adhesion is the rubber ‘sticking’ to the track. Chemical bonds constantly form and break and these bonds create the adhesion force. The amount of this force is dependent only on the force pressing down on the tire, and the coefficient of friction between the two surfaces. Coefficient of friction (Cf) is a dimensionless number that describes how well the two surfaces stick together. This value is different when sliding and when not sliding. The Cf drops off as the tire starts to slide, which means less grip when you’re sliding around. This is not necessarily the case on dirt though as sometimes there’s not much to adhere to. Some dirt tracks will wear in a ‘groove’ and it will be smooth and stable enough to form adhesive bonds. A green track that hasn’t been run on in a while will not have this groove and your tires will have to rely on the following two forces.
Deformation is a result of the surface of the tire bending to match up with the rough track surface, usually on a very small scale. Even very smooth paved tracks have tiny bumps if you look very closely. When it’s wet on a hard track, deformation is the only grip you’ll have, as even a thin layer of water will prevent adhesion.
The last way in which a tire generates grip is through wear. If the forces acting on the tire surface in any one spot exceeds the strength of the rubber, it will begin to tear on a microscopic level. This tearing eventually causes tire wear, and in extreme cases on a very sticky track can cause graining on a tire. As the tire wears, tiny pieces of rubber are constantly being removed. The energy it takes to split these pieces off of the rest of the tire generates force.
The sum of these three forces is the total friction force of the tire. All three forces are directly related to how much contact patch there is, the surface and material characteristics of the two surfaces, and the coefficient of friction. More contact patch always means more grip. This is not to say that tread pattern doesn’t matter, it does matter greatly, but more area of the tire touching the ground for a given type of tire, the more grip.