205/309 Suspension Queries - Corner Weights, Spring Rates Etc

[Ajr 0]

Hi all. I've bought a full 309 GTi suspension setup for my car.

 

I have read that the torsion bars in the 309 beam are 21mm, and the 205 ones are 18mm is this true?

 

If so obviously the spring rate is higher, somewhere around the ratio of 100lb wheel rate for 18mm and 170lb wheel rate for 21mm. If anyone knows the accurate wheel rates for these bars please let me know.

 

However the damper part numbers(aftermarket) are the same! So either the dampers aren't going to be valved correctly or i'm misinformed and the 205 and 309 share the same size of torsion bars.

 

Next questions.

 

I'm going to need some front springs and dampers suitably rated to balance the car with the 309 beam fitted(i have the wishbones & driveshafts too).

 

Does anyone know the rating of the standard front springs? Or the rough corner weights for a GTI6 205?!

 

Any help is greatfully received and i look forward to speccing some nice suspension for my 205

 

Many thanks

 

Alex

[Anthony 1,003]

I have read that the torsion bars in the 309 beam are 21mm, and the 205 ones are 18mm is this true?

No. 205 GTi torsion bars are 18.9mm, and 309 GTi torsion bars are ~20mm

[Ajr 0]

Ok so it's not such a major difference, the rate will still be up to 20lb/in different at the wheel i'd have thought though!

 

I'm trying to work out what springs will give me the balance i want, and which dampers to go for. Need to know weights and rates to work out the resonant frequencies.

 

Cheers for clearing that up

Edited March 23, 2009 by Ajr

[Tom Fenton 1,542]

I don't think the spring rate will end up being significantly different, remember that the 309 torsion bar is longer, hence the twist is being applied over a longer length.

[Ajr 0]

Ah but there is a larger volume of metal in a longer bar of the same diameter, the twist will be slightly less too as the bar is longer from what i can remember!

 

The wheel rate should be a good 20% more i think!

[Tom Fenton 1,542]

Volume has nothing to do with it. Cross section as defined by the OD of the torsion bar, and the length over which the torsion is applied, along with material properties, are used to calculate the torsion bar resistance to applied moment. The spring rate effective at the wheel is then a ratio attributable to the distance from the fulcrum. A shorter torsion bar is naturally stiffer than a longer one due to the length over which the twist is applied. Therefore a LONGER bar (e.g. a 309 bar, compared to a 205 bar) needs to be thicker to retain the same spring rate as a shorter bar.

I think the 309 bar probably does give a slight increase, but no way is it 20%.

[Henry 1.9GTi 36]

what tom said, try to twist a long fresh pencil and then a short old one, same thing.