Suspension Tuning Guide

As every car set up and driver style is slightly different from the next, we wont be telling you exactly what settings to use in any given car. We will however be giving you some industry accepted tips on how to change your set up to suit your car specification and needs.

When we supply a Gaz Coilover kit we go through the process of finding out what the car is used for and its specification so we can have the kit built with the correct spring rates, damper valving and ride height range to suit those parameters. So with us, from the very start, you will have the correct kit specification, it is now just a matter of optimising and fine tuning your set up, with a little insight from what is going on with your cars suspension.

Understanding Grip

Your tyre sits on the road with the weight of the car pushing down on them, the tyres is gripping the road. Simple enough, and a great start – you have some grip!

Now, 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 guide however, we aim to show you how to increase the available grip regardless of the tyres uses. Once you have increased your grip to the maximum by mechanical means, only then will you reap all the benefits of fitting semi or full slick tyres.

So, this grip on the road that you have 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 that occurs when the car is moving. We assume your not going to change the drive configuration of your (changing a front wheel drive car to rear wheel drive car to change its handling characteristics is a bit excessive!) car so we will concentrate on weight transfer and suspension settings.

Weight Transfer – 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 to what is going on. Steer left, body rolls to the right adding weight to the right hand tyres, steer right, body rolls to the left, adding weight to the left side tyres.

Now, if we move weight towards a pair of tyres, grip will increase at those tyres. If we move weight away from a pair of tyres, grip will reduce from those tyres.

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. In some cases the rear can become unsettled enough to loose grip completely allowing the car to spin especially if you are braking hard and turning in at the same time.

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.

We now understand what is happening to our tyre’s grip on the road when we accelerate, brake or turn so let us look at what happens at the limit of grip and what we can do to increase grip.

So, at the limit of your tyres grip whilst cornering, one of two things is going to be happening. Your car will either be understeering or oversteering. We assume that either condition is a result of your car reaching its limit of grip and that you are driving smoothly as your instructors or the books you have read suggest and that you have not induced understeer or oversteer yourself by driving too quickly into or out of a corner.

What do we really mean by increasing grip? Remember we said there was a limit to your cars tyre grip and that it will be either understeering or oversteering at the limit? What we are now going to do is try to increase grip where we need it (and reduce it where we don’t need it) by altering the setup of your car to transfer weight in the most useful way and what other changes you can make to maintain the maximum amount of tyre contact to the road during cornering to corner faster.

As the majority of cars these days are front wheel drive, we will start with reducing understeer!

Reducing Understeer

your car will be trying to plough on straight ahead rather than driving around a corner. Accelerating makes the condition worse, taking your foot off the accelerator and even light braking sees grip return to the front wheels as weight is transferred to them but this takes time. You may run out of tarmac, run onto the grass, hit an armco barrier, tree or some other track hard furnishings.

So, in the understeer condition, say you are turning left, your cars body is rolling right transferring weight and grip to the right pair of tyres. You have some extra grip on these tyres but your car has this overwhelming desire to plough ahead instead of making the turn, it seems to want to run onto the grass, hit an armco barrier, tree or some other track-side hard furnishing with the front of the car. Accelerating makes the condition worse, taking your foot off the accelerator and even light braking sees grip return to the front wheels as weight is transferred to them but this takes time and that barrier is getting closer all the time!

The problem is you have too little grip on the font right tyre and too much grip on the right rear tyre. You need to induce more weight over the front of the car away from the rear.

The Rules Are:

• We know that if we move weight towards a pair of tyres, grip will increase at those tyres. To do this we need to stiffen the opposite end of the car or soften the end we want to transfer too.
• If we move weight away from a pair of tyres, grip will reduce from those tyres. To do this we need to soften the opposite end of the car or stiffen the end we want to transfer from.

So you can see that you need to make the rear stiffer or soften the front. For those of us with adjustable suspension the process is simple enough and just for good measure here is a list of the other things we can do to reduce understeer. The first four you will be able to do with a set of height and damping adjustable coilovers. The rest will depend upon the adjustability of your cars OE suspension arms and the availability of adjustable arms and top mounts to swap your non adjustable arms and top mounts if required (they are not usually expensive items and the change in handling they can make being adjustable parts can be significant).

• Softening the front damping
• Stiffening the rear damping
• Lower the front ride height of the car
• Raise the rear ride height of the car
• Increase front camber
• Reduce rear camber
• Increase toe-in at the front
• Increase toe-out at the back
• Use a softer front anti-roll bar
• Use a stiffer rear anti-roll bar
• Use softer front springs
• Use stiffer rear springs

If your car is not wishing to plough on, it wont be understeering, it will be oversteering. Read on!

Reducing Overersteer

In the oversteer condition, say you are turning the same left hand bend, your cars body is rolling right transferring weight and grip to the right pair of tyres. You have some extra grip on these tyres but your car has the same overwhelming desire hit an armco barrier or that tree but this time it would very much like to spin round and hit stuff with the rear of the car! Again, accelerating makes the condition worse whilst steering into the slide and taking your foot off the accelerator can sort things out quite quickly (unless momentum has already taken over at which point a trip backwards into the trackside scenery is very likely).

The problem is you have too much grip on the font right tyre and too little grip on the right rear tyre. You need to induce more weight over the rear of the car away from the front.

So here is the of the other things we can do to reduce oversteersteer.

• Softening the rear damping
• Stiffening the front damping
• Lower the rear ride height of the car
• Raise the front ride height of the car
• Reduce front camber
• Increase rear camber
• Reduce toe-in at the front
• Reduce toe-out at the back
• Use a stiffer front anti-roll bar
• Use a softer rear anti-roll bar
• Use stiffer front springs
• Use softer rear springs

The Goal

The goal is even out a finite level of grip to reduce understeer or oversteer at the limit to set the car up so that it corners more neutrally. This in turn will allow you to corner faster with more predictability and confidence and hence you will be faster down the straights and your lap times will come down. Without adding even 1 horse power. Awesome.