Correctly setting up Suspension, Anyone know how to do it? Options

[Nial]

I have been doing some research into setting up suspension correctly, I have worked out all the maths to calculate things like the roll centres, all 3 centres of gravity, spring rates, ride heights, sprung weight, unsprung weights, Roll bar rates and so on......... but now I dont know what to do with it...I can tell that the roll centres are X inches high, the locations of the centres of gravity, but whats the ideal? does anyone have any real world experience of setting up suspension on GT4s or any other car for that matter????

[Tom_SS2]

i don't think there is a formula, your best bet is just to set it at a safe setting then take if for a spin and find what you do like and don't like, i just fitted my coilovers set them all on medium and the rear ARB on medium and i'll then see what i like

[Nial]

Ok heres my go at trying to explain the maths behind setting up suspension. I hope I have got it right.

As with almost everything about cars we should have at least a basic understanding of how suspension works, what its effects are and what changes will happen to the suspension set up before we go about messing about with it, as especially ST205 suspension is very expensive and you dont really want to spend large amounts of cash making your car handle worse.

PART ONE - ROLL CENTRE

As the topic is still fresh in my mind I`ll make a start with ride heights and something called "roll centre"

What is Roll Centre??????

Roll center is the virtual pivot point in space that a car rotates around when subjected to cornering forces. The roll center is significant because its location determines how a car will handle and what factors must be considered when tuning its suspension.

How to calculate the Roll Centre?????



Now the above would allow you to calculate the roll centre for a 185, but I`m not sure how the set up of the superstrut suspension would change the way you work out where the roll centre would be.

A usefull program for calculating roll centre

http://performancetrends.com/rc.htm

but it appears you can do a scale drawing of your suspension to do this manually.

Another useful site

http://www.billzilla.org/suspensn.htm

Judging from this diagram




You draw a theoretical centre line of the car, you then draw a line from the lower suspension arm #1 and a line parallel to the spring cup on the shock absorber......where these two lines come together you make a mark. You then draw another line from this mark to the centre of the tyre contact patch, where this line intersects the theoretical centre line is your roll centre

Now depending on what you want to use your car for should dictate where abouts you want your roll centre to be...reading up a few articles, anything from 2 to 4 inches above ground level is what you are aiming for for the front wheels and from 4 to 10 inches for the rear wheels. This is different for a race car but their suspension set up is of course totally different.