Tinea Pedis wrote:
Hence asking if someone could check...
i did the calculation based on ridley's geometry chart and the specs in the article, just on a piece of paper.
i did make some assumptions on the saddle. because i was only able to find the length of the saddle. So in knowing that and using an underside image of the saddle and measuring my computer screen with calipers.... i was able to find rail length from the ratio. Also i assumed that the rails were in the center of the saddle with equal material in front and behind the center point of the rails, this was based on measuring the picture as well. I also assumed that the thomson cradle was 27.2 length. Pictures show it to be slightly longer than the diameter of the shaft however. So i then assumed the clamp could be moved to the very edge rearward of the rails. Also assumed that rails were 25.4mm below the plane of the top of the saddle.
needless to say I'm interested to hear what the guy above me finds out, but the number i got was closer to 82mm which would be the tip of san marco saddle behind the vertical line 90deg drawn through the bottom bracket. I certainly could be wrong though through margin of error on assumptions of saddle
the numbers from the surface seem to make 'sense'. The horizontal distance if there was no saddle , from the bb-top through seattube (816mm) is 239mm, to get to directly above bb. Selle lists the san marco total length as 278mm. So if you imagine crudely the rails being in the middle and being clamped in the middle that would leave ~140 behind and in from of the seat post center. and that's 100mm 'setback'. (i am leaving out the horizontal extra distance because in reality the clamp is clamping the rail at a plane 1inch (assumed) lower than the top of the saddle). And despite moving a clamp fore or aft in rail, it's limited by the outer edge of the clamp, meaning the true adjustability of fore/aft is less than the total length of rail.