Baz 421 Posted January 17, 2008 After searching for a good few hours now, trying to find a thread i'm pretty sure i've seen before that lists all the different size TB's and ARB's that come as std across the PSA range, -without any luck, i thought it would be very handy to have a definitive 'Pinned' topic for that very purpose? For instance, i remember there being a change in ARB and possibly TB sizes at some date for 309 GTi beams? Something like '91 onwards were larger than the previous years versions... and so on. Would certainly be helpful! Share this post Link to post Share on other sites
Henry Yorke 269 3 Cars Posted January 17, 2008 GTI16 had the change on the 309 IIRC Share this post Link to post Share on other sites
pug_ham 245 3 Cars Posted January 17, 2008 Only claimed difference on the 309 GTi is for the front arb which changed from 21mm to 17mm (same as 205 GTi front one) around 1990 but no one has ever found this to be true afaik. Rear bars on the UK spec GTi were 20mm right through production afaik. Like henry says, only difference on rear tb & arb was fior the 309 GTi16 which were 1mm bigger iirc. Graham. Share this post Link to post Share on other sites
McPikie 0 Posted January 17, 2008 So bigger = stiffer, and it's "buy new" or so to speak to change parts?? Share this post Link to post Share on other sites
pug_ham 245 3 Cars Posted January 17, 2008 So bigger = stiffer, and it's "buy new" or so to speak to change parts?? effectively yes. Graham. Share this post Link to post Share on other sites
Baz 421 Posted January 17, 2008 I wa s kinda hoping for a list of what has what standard... Share this post Link to post Share on other sites
markw 1 Posted January 30, 2008 alan knight from the factory special tuning told me that for every 1mm increase in bar diameter you increase the spring rate by 1.5 times Share this post Link to post Share on other sites
niklas 1 Posted January 30, 2008 alan knight from the factory special tuning told me that for every 1mm increase in bar diameter you increase the spring rate by 1.5 times Actually it's like this: diam increase19 - 20 22,8% 21 21,6% 22 20,5% 23 19,5% 24 18,6% 25 17,7% 26 17,0% 27 16,3% 28 15,7% 29 15,1% 30 14,5% Share this post Link to post Share on other sites
pug_ham 245 3 Cars Posted January 31, 2008 Actually it's like this: diam increase 19 - 20 22,8% 21 21,6% 22 20,5% 23 19,5% 24 18,6% 25 17,7% 26 17,0% 27 16,3% 28 15,7% 29 15,1% 30 14,5% Are they incremental increases on the previous increase from a standard 19mm bar? ie; a 21mm bar is 44.4% stiffer than a 19mm one. Graham. Share this post Link to post Share on other sites
Rob Thomson 6 Posted January 31, 2008 (edited) Stiffness is proportional to the fourth power of the diameter. So in the first example above... (20x20x20x20)/(19x19x19x19)=1.227, or 22.8% So for 21mm vs. 19mm... (21x21x21x21)/(19x19x19x19)=1.492, or 49.2%. Edited January 31, 2008 by Rob Thomson Share this post Link to post Share on other sites
Mandic 0 Posted February 3, 2008 niklas says that 20mm in 22,8% stiffer compared to 19, 21 is 21,6% stiffer than 20 and so on... Cheers Ziga Share this post Link to post Share on other sites
