Board logo

how much tension on front springs?
whitstella - 14/1/12 at 06:46 PM

hi just want to know roughly how much tension to put on the front and rear springs?

cheers

mad-butcher - 14/1/12 at 07:35 PM

Not that I know anything, but in a perfect world with correct spring ratings and with the springs compressed to the desired ride height then they should be under the correct tension/compression

tomgregory2000 - 14/1/12 at 07:54 PM

quote:
Originally posted by whitstella
hi just want to know roughly how much tension to put on the front and rear springs?

cheers


None because you cant put tension on them, compression yes as they are compression springs

AdrianH - 14/1/12 at 09:32 PM

My thought on this is that the only way you can over do the springs is if you are tightening against the end stops of the dampers, then either the damper will give of the spring will break if you way over do it.

One the spring is supporting the corner weight of the car all it will do is lift up that corner of the chassis.

Hopefully the spring is long enough so that if the suspension is ever hanging the spring cap does not come loose and have a chance of dropping out. You set the spring platform to give you the desired ride height. You should have enough travel left to absorb bumps before hitting the bump-stop if you have one fitted.

If you have too much roll in corners then you need stronger springs.

Just thoughts in my head.

Adrian

Sam_68 - 15/1/12 at 01:24 PM

quote:
Originally posted by AdrianH
My thought on this is that the only way you can over do the springs is if you are tightening against the end stops of the dampers, then either the damper will give of the spring will break if you way over do it.

The ideal is for the spring length to be such that there is the smallest possible amount of preload at full damper extension, when the car has been corner weighted/ride heights adjusted.

No preload at all and the springs will rattle (and could, potentially, become unseated) at full droop.

Too much preload and at extreme attitudes of skewed roll (for example when the car is close to lifting a front wheel when cornering hard), there would be no movement in the spring despite variations in the load on the tyre, because the load variation is all being absorbed in the preload. This can do unpleasant things to your handling, though it's unlikely to place so much strain on the damper that it fails (unless you apply really stupid amounts of preload.

In practice, because the corner weights will be differenct at each corner, it's never possible to get exactly right spring length to give the desired negligble preload, unless you grind down the spring length to suit each corner to suit. You therefore have a choice between:


  1. selecting springs that are the next available size too long for the 'worst case' corner, and accepting some small degree of preload, or;

  2. selecting springs that are a little too short to 'fill the gap' between the spring seats when the corner weights/ride heights have been set, then using 'helper springs' (very soft springs that become coilbound under minimal load) to take up the slack.

Personally, I prefer the former - for no better reason than helper springs always struck me as a bit of a bodge.

DIY Si - 15/1/12 at 02:27 PM

Sam, what about the variable/two stage type of springs that I have on my rear dampers? They have a soft section that is designed to go coil bound before the longer stiffer stage comes into play. Caterham CSR's have the same set up.

Sam_68 - 15/1/12 at 03:00 PM

Variable rate springs are usually designed to serve a quite separate purpose - to give a fairly compliant ride around normal ride height, whilst rapidly increasing in rate to limit wheel movement so that low ground clearances/susupension movement can be used without the car bottoming altogether.

They're usually more trouble than they're worth (IMHO), 'cos you get rising rate occuring in the diagonal weight transfer that takes place when a car rolls through a corner, and the calculations/tuning of them presents some mind-boggling problems.

They're not intended as a solution to spring/damper length issues. Any professional company, or any properly designed and developed car, will have the right damper length/extension and spring length/extension to give the necessary minimal preload without resorting to bodges like helper springs; it's not difficult. It's just that here in Locostland, bodging and making do with less-than-ideally-suited components is second nature.