Selecting The Correct Springs & Dampers For My Car

[CedricTheBrave]

that was going to be one of my questions! is the unsprung mass the whole unsprung mass of the car or just the corner weight?

[CedricTheBrave]

personally I would expect it to be done for each corner!

[BLiNK Motorsport]

that was going to be one of my questions! is the unsprung mass the whole unsprung mass of the car or just the corner weight?

It is done per axle usually,

you find your front rear weight split using a corner weight set-up, which may give the following for a 1000kg car:

Front axle = 400 kg's

Rear Axle = 600kgs

You then have the following averages/wheel - 200kg's front

300kg's rear

These weights are the sprung and unsprung mass together.

You then need to weigh the components of the unsprung mass; wheel,brake calliper, hub&bearings, wishbones,damper&spring etc (you use only half the weight of some of the components such as the damper/spring unit).- Lets say 30kg for the front axle components/wheel.

This figure (30kgs) is then subtracted from the above figure (200kgs) and this gives you the sprung mass per wheel. (170kgs)

It is this figure that you use in the formula.

The Motion Ratio in the calculation is critical; the spring rate needed is much higher than the wheel rate due to the inclination of the spring and the lever arm ratio of the lower wishbone.

HTH

[rocket_rabbit]

(Just as an aside; F1 & other full Aero Cars run at ride frequencies just over 5Hz. This is required because the aero force generated compresses the springs so much that they need to be such a high 'poundage' to maintain ride heights. The human body can just stand this - the ligaments holding your internal organs in place start to suffer around 4.5Hz and you organs start to bang into your skeleton causing bruising!)

I know they have heave springs to compensate for downforce.

I enjoyed reading the article BTW, but tyres are a motherfecker that could quite easily destroy best laid plans.

I know you said it was a basic overview and I can well believe it, but do you compensate for torque loading via suspension arm fulcrum to damper to loading distances? Do you go further and start looking at damper angle.

And referencing the linear damping motions - would you not want a digressive damper on track, albeit with a higher change point to accommodate curbing? I'd have thought the last thing you want is impulse weight transfer to the tyre already on the edge of grip?

[CedricTheBrave]

Do we know what the lever arm ratio is for the front and rear of a Westy?

[BLiNK Motorsport]

Do we know what the lever arm ratio is for the front and rear of a Westy?

You have to measure the Motion Ratio for individual vehicles (Westfield front suspension varies depending on design)

[CedricTheBrave]

motion ratio = wheel movement/shock movement ?

[John Loudon - Sponsorship Liaison]

Just the corner weight but you have to subtract the unsprung weight of the wheel and the hub, brake dis, caliper etc from it. There's plenty of info on the net about how to calculate it all but they tend to use cycles / minute rather than Hz. (1Hz = 60 cycles / minute)

[AdamR]

Bit of a bump, but doing some research!

motion ratio = wheel movement/shock movement ?

That's what I can work out too. I am guessing the distances are measured from the lower wishbone pivot to the centre of the tyre, and from the wishbone pivot to the shock mount. I am getting 1.66 at the front (500mm and 300mm) and 1.5 at the rear for my car (600mm and 400mm)...

The difference in spring rate required to go from 1.5Hz to 2.0Hz suspension rate is very surprising (although I guess on the other hand it's not, since the frequency is squared in the formula...).

[AdamR]

Been doing some more reading / spreadsheet-ing tonight, this is a handy link: http://www.startline...l26/springs.htm