Measuring chassis stats

[Output Flange]

How do you measure the following:

1. C of G height
2. Roll centre height
3. ARB lever length

?

TIA

[Nick1point9]

Output Flange said:

How do you measure the following:

1. C of G height
2. Roll centre height
3. ARB lever length

?

TIA

C of G height is very difficult to accurately measure, but will require some accurate corner scales (preferably reading to the nearest 0.1 kg) and a ramp to lift one end of the car. Then there is some trigonometry to do to calculate the C og G height based on the angle change of the car and the subsequent movement of weight. It's not a great method and fluid slosh/suspension travel blurs the result. Another method (used by many vehicle manufacturers for modelling/validation) is to mount the car on a (virtually) frictionless bearing and bounce one end against a spring. Incredibly expensive to do (probably min £10k at somewhere like Cranfield), or you can do it by modal analysis of the car (extremely expensive hardware/software required and a lot of know how required).

Roll centre height can be derived from suspension geometry. Reasonably simple on double wishbone suspension cars, but can't say I've ever done it for any other suspension type. Providing you have accurate measurements of inboard and outboard hard points it's pretty simple.

ARB lever length is very simple, it's the perpendicular distance between the centre of the ARB and the line of force through the drop link. Take accurate measurements and it can be derived through trigonometry but will usually change as you go through ARB travel (this gives the ARB an increasing or decreasing rate at different levels of roll.

Curiousity has gotten the better of me, what are trying to achieve?

[Output Flange]

Thanks for the info.

I'm looking to get some coilovers made for my race car, for which they want the above information amongst others. Some of it is simple to get, some isn't.

The same company made a set for a previous car of mine, but had already built some to the same spec, so had everything they needed. This time they don't.

[Nick1point9]

What car is it?

[Output Flange]

BMW E28 535i

[Nick1point9]

Surely there must be some off the shelf coilovers for a BMW? I'd imagine you'd have choice over spring and damping rates too, it's hardly a rare car! I had something much more exotic in mind!

[Output Flange]

The choice is very limited for E28s as so few are still around. It's on Gaz now and they're rubbish, so looking to go to something better - I had Black Art Design 3-ways on a previous M3, so looking to get them to build some for this car. The problem being, they've not done them for an E28 before so need all the stats.