Pat's Column - Car set up

Von: Pat Clarke

Apologies to all for the lack of a column over the last few months. Insane work pressure has kept me away from home for 7 of the last 9 weeks.

Last week had me in Adelaide where I witnessed the finish of the Solar Challenge. It was almost like being at a FS event as the front running universities all have active FS/FSAE teams.
Special congratulations to Tokai, who won the event over all and to Uni of NSW and Uni of Michigan at Ann Arbor who took the podium places. Incidentally, our friends from TU Delft have won the event on four occasions, in 2005 setting the record of 102.8kph for the 3000km crossing of the Australian continent. I am sure there is a huge store of electric vehicle information at Delft which will be shown to us in FSE!

When the Solar Challenge was started, the area of solar panels on each car was limited to 8m² based on the fact that each person on planet Earth has a potential space of 8m² of ground. The performance of cars like the Delft ‘Nuna’ forced the organizers to lower the area to 6m² and that may well be further reduced to 5m². Like FSE, the organizers are well aware of diminishing global resources and are doing something about it!

I like the idea that a car is like a Rubik’s cube puzzle, in that any adjustment causes changes in unexpected areas, just like setting up a car.

Car Setup, another variation on the Rubik’s cube.

Have you ever tried to solve a Rubik’s cube? You get one or two sides solved and then no matter what you do you mess up what you have achieved in trying to advance further.
Car setup is similar. Each time you improve one aspect of the handling, something else goes away. An example would be you have under-steer on turning into a corner so you do some adjustments to improve the turn in only to find you now have trouble putting the power down coming out of the corner!

Assuming the car is finished in time, the limited availability of track time and the cost of private practice means that most teams never get enough time to properly sort the car. Even worse, their drivers don’t get enough seat time to stabilize their personal performance so their ‘seat of the pants’ feedback is unreliable.

The availability of relatively cheap data loggers has not really helped because, in amateur hands, they tend to have the setup engineer (often the driver) micromanage the situation by concentrating on insignificantly small increments of too much data. How often do you hear a driver say something like “Toe it out half a millimeter and see what happens”.  Michael Schumacher might feel a tiny adjustment like that but the average FSG driver will not and by attempting to do so will lose a track session. Some common sense logic needs to be applied.

First, it is important to know that the basic setup of the car contains no hidden flaws that will lead you astray. These settings need to be noted in a notebook and any changes recorded. You do keep a setup diary, don’t you?

• Check that tyre diameters are equal across the car (L R).
• Place scales (bathroom scales?) in position to go under the tire contact patch. With a straight edge and spirit level, shim until the scales are level across the car. Fore & aft is not so important. With the driver in position, use ramps to roll the car onto the scales.
• Disconnect the anti-roll bars (if fitted).
• Set the ride height and cross weight.  If the car is heavier, front plus rear, on one side it is not possible to equal both the front an rear unless something can be relocated across the car, if not then the front is the most important to make close to equal because of its effect on braking.

You are now ready to set the suspension, KPI, Caster, Camber and Toe. Ensure the steering is locked in the central position.
If you have prior setup knowledge use it, if not check that the KPI and Castor are the same on both sides. It is not generally understood that both Caster and KPI will cause a change in camber as the wheels are steered.
High KPI settings can cause the outside front wheel to develop positive camber which destroys both grip and tyres.

Baseline settings for Camber and Toe are as follows

For cross ply tires.
Camber front, 1° to 2° negative, rear 0° to 1° negative. 
Toe out front ½°.
Toe in rear ½°.

For radial tires.
Camber front 3° to 4° negative, rear 1° to 2° negative. 
Toe out front ½°,
Toe in rear ½°.
Make sure settings are even side-to-side.

If the front toe is not set evenly on each side, the toe will automatically centre on the track as a result of the caster/KPI effect. This will put the steering wheel off-centre and will upset any ackermann angle side to side.

If the rear toe is not centered, this will cause the car to ‘dog track’ on the road and will also cause the steering to go off centre as the driver corrects. It is very worthwhile to make sure the front and rear toe is equally split.

A mistake often made by students is to measure toe at only one side of the wheel, usually the front at the front and the rear at the rear. If you do this you must remember to adjust the toe you are measuring to only half the desired figure. Remember, the other side of the tyre where you are not measuring is moving too!

Finally, connect the anti roll bars; adjusting the links so there is no preload.