Droop

Droop is determined by the amount that the chassis can lift from normal ride height until the wheels lift off the ground.

When the car turns a corner most of the weight of the car is transferred to the outside wheels. If we had a fixed axle front and rear, the inside wheels would lift. But because our cars have independent suspension we can compensate for this. By giving our cars droop we allow the springs to exert pressure onto the inside wheels give us more traction at the front, reducing under steer. And increasing traction at the rear, preventing spin out and diff-out.

The droop is adjusted at the front by adjusting the screws on the lower wishbone. Screw out the screw-more droop. Screw in the screw-less droop.

On the rear this is usually adjusted on the top wishbone, screw in the screw –less droop. Screw out the screw-less droop. Remember, too much of something can be as bad as too little.

To start with, 3-6mm front. 4-8mm rear shouldn’t be far away.

Caster Angle

The purpose of caster angle is basically to allow the front wheels to self-centre. Imagine the wheels on a good shopping trolley (if you can find one), if you look at the wheels the spindle of the wheel is not directly below the mount but trailed back at an angle, this is the caster angle. When you push the trolley the wheels all point in the direction of motion so are self-centred.

All rear wheel drive cars have positive caster on the front wheels.

Neutral Caster  Positive Caster  

Although the main reason for the caster angle is to self-centre the wheels the angle can affect the car handling as well. Too much caster and you can get what is known as wheel shimmy. This is when the front wheels flick side to side rapidly .Too little caster can make the car oversteer and be a little nervous. The caster angle is adjusted by sliding the front wishbones on the hinge pins. To increase caster slide the top wishbone back or the bottom one forward or a bit of both, and do the opposite to reduce the caster. It is very difficult to measure caster angle so it is more a case of trial and error to get the correct setting.

The best starting point would be both wishbones in the centre of the hinge pins as there is positive caster built into the steering hubs.

Ride Height

Just a quick one on the car ride height. Try to run the car as low to the ground as you can without the chassis scraping the ground. Ride height is adjusted on the collars of the shocks, screw them down increases the ride height and visa-versa. Set the rear end a couple of millimetres higher than the front.

This is just the basic car set-up and will get your car round the track. Next we will go into more depth and detail about different changes.
If you wish to alter the settings only change one at a time to see if there is an improvement, don’t change two or three at a time as you will not know what has worked and what hasn’t.

Always remember, there is no such thing as a perfectly set up car. There is always a compromise, give to the front and you loose from the rear, give to the rear and you loose from the front.
 

Often overlooked and underestimated. The ride height of your car will determine a few things. Firstly and most importantly it will affect the centre of gravity of your car. The higher the ride height, the higher the centre of gravity. This will affect your cars ability to corner.

Let me explain: The centre of gravity of your car is basically where the centre mass of the car is, front to rear, side to side and height above the ground. All these factors will converge at one point on you car to determine the car’s centre of gravity. Apart from moving fuel tanks and battery packs we are limited to the amount of changes we can make to the linear centre of gravity. What we can do is affect the lateral centre of gravity.

When your car is travelling full speed up the straight it wants to keep travelling in a straight line. When we get to the end of the straight we want to turn the corner but the car still wants to keep going straight on. Now we have to think about leverage, the longer the lever, the more leverage. If your lever is 25mm long and you double it to 50mm then you double the amount of force applied. Now to apply it to the cars, if you run with 20mm ride height then drop to 10mm ride height you will have half the amount of force trying to push you in a straight line so it will let you turn the corner easier and quicker.

The front of the car should be a bit lower than the rear to allow for weight transfer during braking and cornering.

Run the minimum ride height that the track conditions will allow to prevent the chassis from Scraping the ground at every corner.

A good starting point is front-6-10mm and 8-14mm rear.

The dampers fitted to your car are there to ensure that the tyre remains in contact with the track at all times. The springs are fitted to support the weight of the car and prevent the chassis from scraping the ground.

That’s the basics, now for a bit of fine-tuning...

I am talking about oil filled dampers here. No matter what spring rate the springs are, the oil in the shocks must be the right viscosity to counteract the spring oscillation but still allow the piston to travel through the oil. In other words it stops the car bouncing up the track but still allows the car to soak up the bumps.

The shock oil is graded in numbers, the lowest number being the thinnest oil and visa-versa. Different manufacturers have different number systems so pick a brand and stick with that one brand throughout so you have a common reference.

To be precise you must ensure that all the wishbones are free to move and none of the hinge pins are bent. Remove your shocks and wheels and put the chassis on a block to clear the surface. Disconnect any anti-roll bars. The wishbones should lift and drop with no tight spots or resistance. If there is any, solve the problem before testing the shocks. Now re-fit the shocks and wheels and put the car on the flat surface.

To get the car to its normal ride height you must push down and lift the chassis a couple of times finishing with a push on the chassis. Release the chassis and let it rise on its own. Now without pressing on the chassis, roll the car back and forth about a car length. This will ensure the tyres don’t have a grip on the worktop.

You must do this every time you test the shocks.

Now, to test the rear spring/oil balance, push the rear of the chassis down to the stop and release. Note how the chassis returns to its ride height. If the car springs back straight away then the oil is too thin. If the car starts to rise and stops then the oil is too thick.

What you want is the car to rise up to its normal ride height under the control of the dampers.

If you don’t know what oil is in the shocks to start with have a starting point. This depends on the spring rate, if it’s a soft spring start with thinner oil and the same with stiffer spring use thicker oil.

You may have to buy 2 or 3 bottles of oil for both front and rear to get the exact oil/spring balance but it is well worth a few pounds to get it right. And the oil you don’t use can be used if you change springs or do a bit of tweaking to suit track conditions which I will cover later.

If you want a bit of a reference try it on your full size car, push it down and release and you will see it slowly returns to its ride height.

Now we have covered the balance between the oil and springs I will just say a bit on the springs themselves.

In general the springs on the front should be stiffer than the springs on the rear.

This may confuse some people as a lot of cars come from the factory with stiffer springs on the front or the same on both. To simplify matters, the softer the spring the more grip. So to get the drive to the rear wheels we tend to put a softer spring on the rear, within reason. 1 or 2 spring ratings of a difference is enough. As long as you have the oil matching the spring you can balance the car with toe-in, camber etc.

Always remember, car set up is a compromise. What you gain at the front you loose at the rear and what you gain at the rear you loose at the front.

I have gone on a bit about spring/oil balance but it is essential that whatever springs you have the oil in the shocks should match them.

Just a quick note, if you have some fancy pistons fitted, the set up is the same; the oil still has to match the spring.

Camber Angle

Camber angle is the angle of the wheel when viewed from the front or rear of the car. There are three possible angles, positive camber, neutral camber and negative camber. If the top of the wheel leans into the centre of the car you have negative camber. If the wheel is vertical you have neutral or no camber and if the wheel leans out you have positive.

Neutral or no Camber Negative camber.

Imagine you are driving your full size car round a fast right-hand corner, the body rolls to the left. The same happens to the wheel, If there is no camber on the wheel the top of the left wheels will lean out and you will end up running on the outside rim of the tyre. To counteract this we put negative camber on our wheels. This allows the wheel to tip over in corners but still maintains full tyre surface contact on the track giving maximum grip on corners.
The camber is adjusted by lengthening or shortening the top wishbone (usually the top but if it is at max adjustment then adjust the bottom).
A good starting point is 2 degrees negative on the rear and ½ to 1 degree negative on the front.

Toe-in & Toe-out

These angles are the direction the wheels are pointing when looking at the car from above

Neutral Toe  Toe out Toe In

The above pictures show the toe angles on the front wheels only but the same rules apply to the rear wheels.
I am not going to explain in any depth why we have these angles as this will be covered in later articles. What I will say is that on a rear wheel drive car the front wheels will have neutral toe or toe-out. The rear wheels will have neutral toe or toe-in.

With the correct toe angle on the front you will have a stable car that has good front end grip.
The correct toe angle on the rear will give good rear end traction through corners.

The front end toe angle is adjusted on the steering links or track rods as they are called on a full size car. Shorten the links – more toe-out, lengthen the links –less toe-out.
There are different methods to adjust the rear toe angle depending on which make and model of car you drive, almost all adjust the rear lower wishbone to give desired angle.

To measure the toe angle is not easy, one method is to use the camber gauge. If you want 1 degree toe-in set your wheels up with one degree of negative camber. Take a measurement from the top centre of the inside rim on the left wheel to the top centre inside rim of the right wheel. Do the same for bottom centre inside rim on both wheels. Transfer these measurements so that the distance top centre is the same as front centre on the inside of the rim, this sounds complicated but when you try it it’s not that bad. Another way of putting it is measure at 12 o’ clock and 6 o’ clock and transfer to 3 o’clock and 9 o’ clock.

Start settings are 2 degrees toe in at the rear and 1 degree toe-out at the front.