About grip

Summary

Grip, aka traction describes how much friction your tires are generating at a given time between themselves and the racing surface, whether it's carpet, asphalt, astroturf, dirt, or your living room floor.

Most of the work we do with tuning RC cars is to make them handle properly given a certain grip level. For high-grip tracks, you'll want to make different suspension adjustments than you would for low-grip tracks.

Grip can be increased through:

Weight
Aerodynamic downforce
Contact surfaces (tire & track)
Suspension tuning

Weight

Weight increases grip, but we don't want our car to weigh any more than it needs to, so let's look at the other two options first.

Tires

Start by generating as much grip as possible through proper tire selection (particularly tire compound) and tire preparation (often with additives.) Ask around at your track and see what tires other folks are running and what additives they're using - that'll get you started, and then you can experiment from there.

Aerodynamics

After that, look at your car's body, the body position, and the wing. Your body and wing generate downforce which will increase your grip at speed without adding weight, but they'll have little effect at low speeds. Body selection and mounting are particularly important for on-road racing (e.g. touring, GP, or drag) and dirt oval racing. Again, it's a good idea to see what folks are using at your local track to get started. For off-road racing, wing placement is the most important factor here.

Suspension

So, once you're getting all the grip you can from your tire and body choices, now it's time to look at your suspension.

The general rule for low-grip tracks is to allow the car to roll more which will generate more grip by allowing the car's weight to transfer to the outer wheels in a turn. To allow more roll, you can lower the roll center.

On high-grip tracks you want the car to roll less because it already has plenty of grip. By limiting the roll, you will improve the car's stability, steering, and responsiveness.