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????

[nics]

it really depends on you. you are the driver so you're the one that will tune the suspension based on how you want your car to bahave when driving it.

[Culpable04]

it really depends on you. you are the driver so you're the one that will tune the suspension based on how you want your car to bahave when driving it.

this is only half true, in the end the driver is the one who will fine tune the suspension, but Nial is looking for the theorically " perfect " suspension for his application and how that translate into reality, he basically has the theorical numbers but he wants input on how this number / formulas translate in real world, that way he can use the info that he has obtained to setup his car.

I have a book that talks about this, will try to dig it from its grave, and see if I can scan some of the pages that are relevant.

[azian_advanced]

i don't have any experience but i think you'll need some sort of dynamic simulation program and create a model with the chassis, suspension components and suspension points accurately designed to 'spec' including the centre of mass to calculate the stresses on the chassis and the reactions of the suspension based on various road conditions and driver input.. of course you'd have to optimize handling by adjusting the suspension and see how the model reacts in the simulation. that would be the best approach to figure out what the 'ideal' settings are for your application.. but would take weeks or even months to complete.

also, i'm interested in this 'data' if you care to share it with us..

[nics]

op, whats your "ideal" conditions?

ideal on track/tarmac?
ideal on snow?
ideal on mud/gravel?
ideal on street driving?

[Nial]

op, whats your "ideal" conditions?

ideal on track/tarmac?
ideal on snow?
ideal on mud/gravel?
ideal on street driving?

Well theres only two of those to chose from really, the car will only ever see either the track or the street. Ideally I`d set the car up for tarmac which would be a halfway house between ttaking it to the track and taking it out on the weekends for a drive about.

If people are genuinely interested in the maths involved in working this stuff out I can "try" and write it up. Its not that complicated.

This post has been edited by Nial: Jun 23, 2010 - 1:51 AM

[RvA944]

Nial,

I'd love to see the math behind this. I'm juts getting into autox and setting cars up, so this might be good for me to learn.

Best,

Roger

This post has been edited by RvA944: Jun 23, 2010 - 1:02 PM

[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.