s3 coilover spring rates

[daz-20vt]

hi guys
im probably going to regret asking this but after speaking to BC today about their coilovers they have advised me to work out my spring rates or find some from more proven coilovers for them to match

they were really friendly but openly admitted to not having a great deal of experience with the s3.

their stock spring rates are

front 7kg per mm
rear. 11kg per mm

does anyone have any idea what this would be like?

thanks guys, daz

 

[antwan64og]

Looking at the 8N TT as its a close neighbour

http://www.ttforum.co.uk/forum/viewtopic.php?t=264970&p=2247835

it looks like street front spring rates start ar 60 kg/mm to 100 kg/mm for track worthy Kw clubsport.

Rear rates look to be slightly stiffer than front for performance orientated set ups.

 

[<tuffty/>]

You had the car weighed at bills... send them that data... they must be able to recommend something from that I would have thought?

<tuffty/>

 

[daz-20vt]

typically the brands worth matching have no rear stats haha

would the tt be a fair enough match with weight distribution and my car is stripped so how would this effect things?

i reckon i need to ask for a stiffer front but would the rear need changing?

 

[daz-20vt]

i thought so to tuffty

i did make them aware it was weighed by each corner but they said im best checking other tested spring rates lol

nice enough phone manner but not over helpful sadly

 

[Prawn]

You need a fair bit more than corner weights to calculate spring rates sadly.

The front end is pretty simple, but on the rear as it's not 1:1 motion there's a leverage involved which changes the rate drastically.

You also need to decide on a target wheel frequency that's best suited to your tyres and driving style.

 

[daz-20vt]

You need a fair bit more than corner weights to calculate spring rates sadly.

The front end is pretty simple, but on the rear as it's not 1:1 motion there's a leverage involved which changes the rate drastically.

You also need to decide on a target wheel frequency that's best suited to your tyres and driving style.

so what you are saying about the rear having leverage would explain why the top brands use a progressive rear spring??

to be honest im not entirely impressed with having to match to another coilover.

whats wheel frequency and how do i figure that out lol

 

[Alex C]

you want to choose a wheel frequency based on your use case; the more track orientated the higher the frequency.

Road car 60-80cpm
Fast Road 80-100cpm
Race car 100-125cpm
Race with aero/ground effect 200+cpm​

60cpm = 1Hz

The 'motion ratio' of the rear spring is the ratio of the distance from pivot point to rear spring seat and the pivot point to the centre of the tyre contact patch. Basically because the spring is inboard of the wheel when you wheel goes over a bump and is deflected by say 5cm the spring is compressed less than 5cm so your spring rate will need to be stiffer to get your desired wheel rate

I'm only aware of this stuff because of trying to get a competitive car in racing games/sims (+it's interesting)

@Prawn The final spring rate is further complicated by the fact that the rear strut is inclined at an angle rather than vertical?