Your tyre’s grip on the road allows you to accelerate, brake and turn. There is a limit to the amount of grip your car will have depending upon a number of factors such as the drive layout (RWD, FWD, 4WD), weight distribution within the car, suspension setup and weight transfer. We could of course increase grip by fitting sticky track day tyres and be done with it (although the high side loads generated by these tyres will quickly ruin your OE dampers or road biased coilover kit very quickly). In this article however, we aim to show you how to increase the available grip regardless of the tyre uses. We will assume you won’t be changing the drive layout or weight distribution in the car and so we will concentrate on the changing the suspension setup to increase grip after we have explained about weight transfer and it’s affect on grip.
Weight transfers occur as a result of the chassis twisting around the car's roll centre. In simple terms, whilst accelerating, braking or steering, your car’s body “rolls” in the opposite direction. If we move weight away from a pair of tyres, grip will reduce, if we move weight towards a pair of tyre, grip will increase.
It stands to reason then, when you accelerate, the weight of the car is transferred towards the rear of the car, the rear suspension compresses and grip at the rear increases whilst decreasing at the front. In a rear wheel drive car this increase in grip at the rear can help to reduce wheelspin, whilst in a front wheel drive car, as the front wheels loose grip due to the rearward weight transfer, wheelspin becomes more likely. The opposite happens when you brake, the weight of the car is transferred towards the front of the car the front suspension compresses and available grip at the front increases whilst decreasing at the rear.
When you turn a corner, the weight of the car is transferred laterally. If you are turning right, weight is transferred towards the left side of the car, the left side suspension compresses and available grip on the left side of the car increases whilst decreasing on the right hand side (and vice versa). It is worth noting that weight transferred whilst cornering can increase grip and get you through the corner quicker ONLY if the steering is used progressively and weight is transferred smoothly. However, if you turn into the corner too quickly, the sudden transference of weight can unsettle the car and cause the tyres to break traction suddenly often resulting in a spin.
So now we understand what is happening to our tyre’s grip on the road when we accelerate, brake or turn we, can look at increasing grip where it is needed. We will assume you have reached the limits of your available grip whilst cornering and that one of two things is happening, your car is either understeering or oversteering. Please see the appropriate guide for Reducing Understeer or Reducing Oversteer but first, let us consider the most basic of modifications that will improve any cars grip on the road.
Suspension bushes help maintain a cars geometry during cornering if they are worn out on your car, it probably isn’t griping as well as it did when it left the factory! Rubber bushes are used by car manufacturers to give a compliant ride as well as suspension location. Uprating your cars suspension bushes to hardened rubber or polyurethane bushes will help reduce geometry changes further to maximise suspension performance.
Strut braces and chassis braces will also reduce suspension geometry changes by reducing flex in your cars body shell. Uprated bushes and bracing bars should be right at the top of your list of suspension upgrades! If you are embarking on a serious track-day build, a roll cage will not only protect you but also does a wonderful job of reducing chassis flex helping to maintain suspension geometry too.
One Last Idea!
Just altering your driving style can improve things! Your tyre will have longitudinal grip (front to back) which allows you to accelerate or brake, and lateral grip (side to side) which allows you to turn. If you are using all the grip longitudinally for braking, you won’t have any grip left for turning. Getting all your braking done in a straight line before you turn will give you maximum grip for turning when you release the brakes and turn in, invaluable advice for those in the early stages of track day driving!