Increase in rear torsion bars from 20.5mm to 21mm equals what?

[Jim (6)]

I would like to ask what the formula is to work out the increase in stiffness from using a 21mm torsion bar compared to 20.5mm.

Thanks

Jim

 

[R. N. Robinson]

I would like to ask what the formula is to work out the increase in stiffness from using a 21mm torsion bar compared to 20.5mm.

AIUI torsional stiffness varies with the cube of the diameter, so your 21mm bar should be about 7.5% stiffer, all other things being equal (and if I'm right).

Ron Robinson

 

[Dave Baker]

Subject: Re: Increase in rear torsion bars from 20.5mm to 21mm equals what?

AIUI torsional stiffness varies with the cube of the diameter, so your 21mm bar should be about 7.5% stiffer, all other things being equal (and if I'm right).

Ron Robinson

It's the fourth power not the cube.

Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.

 

[Jim (6)]

This is based on my assumption that the rear torsion bar is 40" in length and the arm length is 10". Used only an estimate to how much the SW 21mm and PS 23mm rear torsion bars would increase spring rate by.

Does anyone have the exact total length of the rear torsion bar and arm length?

20.5mm 124.95lbs OE spec.

21mm 137.60lbs Increased by 10.4%, 13 lbs

23mm 197.99lbs Increased by 58.4%, 73 lbs

Thanks

Jim

It's the fourth power not the cube.

Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do

though.

 

[R. N. Robinson]

It's the fourth power not the cube.

You're quite right. Sorry about that - need new specs. New brain wouldn't come amiss either.

Ron Robinson