petert 588 Posted August 11 (edited) The material doesn't make a lot of difference, as the Modulus of Elasticity for all steels is within a narrow range. What does matter however, is that it doesn't go past its elastic limit during service. OEM torsion bars are hardened and tempered for example. I think they are made from a plain carbon steel, 1085. I had a 3 pairs of 21mm bars made a long time ago from 4140. We thought being a stronger steel they wouldn't need hardening. They all failed and had to be hardened & tempered. The 23mm bars made from 4140 at the same time, have been fine ever since, without heat treatment. The torsional resistance is proportional to the 2nd moment of area. ie J = pi()d^4/32 Thus being to the fourth power, a small increase in diameter makes a huge difference in stiffness. Going from 19 to 21mm is big, but 21 to 23 is huge on torsion bars. Ditto with ARB's. I run a 25.4 (1 inch) ARB which is a significant step up from 24mm (25% stiffer). Going to 28.5mm is massive. Also massive in price. I'd keep looking for a GTi6 bar to start with and spend the dollars on torsion bars, if tarmac is your thing. I put the std ARB back in on wet days. The lesser 306's such as XSi and HDi only have a 22mm ARB from memory. The Xsara VTS (XU10J4RS) is also 24mm. Edited August 12 by petert 1 Share this post Link to post Share on other sites
Tom Fenton 1,542 Posted August 12 The way I shorten the GTI6 24mm bar is to bore out the one end plate to 24mm all the way through, you can then put a prep on and get 2 nice welds inside and out from the end plate to the bar. It also means you can dummy assemble it into the beam to get the fitted length just right. There is one end that lends itself better to being welded, you'll see which when you come to do it. Pre heat and then oil quench is how I do it, I've done quite a few now for my own cars and other people, no failures that I know of. Share this post Link to post Share on other sites
