Torsion Bar 'spring rates'

[mattsrallye]

Afternoon all

Hopefully this hasn't been covered before, I tried a search and didn't find anything.

Does anyone have any information about the effective spring rates of different diameter torsion bars? I appreciate it's not a straight forward linear spring rate because the bars aren't concentric with the trailing arm bearings but if anyone has any info. at all I'd be interested to know.

The reason I ask is that I'm planning to lower my beam at some stage in the future and swap the bars from 19mm to 20mm diameter ones at the same time. If I was to simply raise the hub by 30mm and fit the new bars as usual the car obviously wouldn't sit 30mm lower because of the stiffer bars, so I'm wondering how much extra the hub would have to be raised to account for the additional stiffness (giggedy)?

...and I'm too lazy to do it by trial and error, I'd rather get it right first time!

[Eeyore]

Are you going to mathematically work out what angle it needs to be at? D:

there is a thread somewhere with all the ratings listed but cant find it atm.

[zx_volcane]

just stick them in roughly (giggity) - lower the car and see how the ride height is

takes minutes if your splines are free n greased up

[mattsrallye]

Well yes, maths was the plan! I've done some rough calculations based on some values I found - mostly because I was bored at work - and I think the 20mm bars would effectively raise the car by 24mm if they were reinserted in the same position, but I guess I'll have to put that into practice when the time comes and see if I'm anywhere near right.

I suppose to check the ride height the anti roll bar won't need to be refitted so that saves some time in the checking/adjusting process? (not done this before see)

[powerandtorque]

That does sound broadly in the right ballpark judging from fitting uprated TB's to various 205's over the years.

Reducing the shock-shock centre distance on the dummy shock by somewhere in the region of 8-10mm per extra 1mm diameter of TB should get you close, but you'll probably need to tweak it slightly to get it exactly where you want it.

[welshpug]

If youre going 20mm bars then 322 is a good figure to go for, standard is 330, not enough travel or spring rate to go lower really as you end up on the stops all the time.

[mattsrallye]

Thanks guys that's useful info. Welshpug I assume that's hole centres for the damper? What does that relate to in terms of an overall drop? I'm only after a 30mm drop from the standard tractor spec

[welshpug]

Itll be about 25mm