Anthony wrote:
One decent approximation of what type of fork a frame was designed for is to fit any old fork and a pair of wheels and measure the bb drop with that fork (i.e., the height of the bb centre relative to the hub centre). XC frames were invariably designed for a 30-35mm bb drop, so if you have a bb drop of say 15cm that is a clear indication that the fork is longer than the frame was designed for. The bb is about 40% of the way from the rear hub to the fork, so 15-20mm too high a bb indicates that that particular fork is 40-50mm too long, which gives you a general idea of what length fork to fit to give the intended head angle.
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You sir are a genius!!!
I've been trying to work out the right forks height for a 2003 XC/trail frame for ages. 99 pace forks seemed low (racy feel but twitchy and not great d/h) and 2006 + 2007 forks of different manufacturers, yet all with same travel and intended purpose were too tall (great d/h handling but poor climbing and straight line pedalling efficiency) . According to the manufacturer the frame geometry didn't change right up to 2009 when it was discontinued.
As you say the manufacturer only gives the usual "designed for 100mm forks giving head angle of 71". Although they did send the frame angles/measurements to me, i didn't have an accurate way of measuring angles. Plus they don't say if the 71 degrees is the standing angle or the riding angle (i.e. with fork sag)
I'm going try your theory and see what I get. If only they included forks on the frame diagram this would have been so much easier!
Thanks for this
