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Old 06-16-2020, 06:48 PM
owly owly is offline
Senior Member
Join Date: Oct 2015
Location: australia
Posts: 420
Will going to a 5mm longer crank upset weight at bars?

Been using 172.5mm arms for a few years. A couple of years ago when hunting around for a suitable gravel frameset, the Competitive Cyclist fit calculator suggested in its numbers that I use a 177.5mm arm.

When I fit anything larger than a 700x33 tyre, I find the ride height too tall and haven't been able to get used to it / like it. So rather than shell out quite a bit of money for a new frame with a lower bb, I am thinking that longer crank arm will pull me down about 5mm into the bike, which should offset running a 35mm. (I'm hoping to be able to try a 38mm ideally; achieve a good ride feel/height).

I think I'm correct in thinking that longer arm length will pull me a bit forward in the saddle when the arm is pointing forward (parallel with ground), and thus at the bars my balance in the bike would now be too far forward. I would need to move my saddle back a bit to compensate, however I can't really move my position back as my cleat fore/aft position is locked into place in the shoe.

I have experimented with moving my cleats forward a mm at a time in the past. When they get to a little over 2mm forward, I start getting some numb toes.

So in summary is there any way to run a longer crank arm and still find the right fore/aft weight/balance feel when riding, by tweaking component position? or am I going to run into trouble?

Edit: Geometry/maths speaking, is a lower bb position the only correct (fit) solution here?

Last edited by owly; 06-16-2020 at 06:54 PM. Reason: txt
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