Stock - 20mm. Addco - 25mm. IPD - 28mm. Volvo R-Sport 1"/26mm.

Not really the place for this comment but, although I've never run one, the IPD bar has always seemed to be much too thick for a road car. I believe the diameter was used on their race 142 and that might have been fine. Can someone say if all of the IPD bars are the same across the 120 and 1800 range? Same as the 140 bars? Explaining it much better than me, the linked article says that going from the standard 20mm/3/4" bar to a 26mm/1" one, increases the stiffness by 300%, so the IPD one is at least 400% stiffer and that's a lot.

http://www.hemmings.com/mus/stories/2006/09/01/hmn_feature19.html