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Old 03-11-10, 05:53 AM   #1
xfimpg
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Bike Fit Question: Change your crankarms, lower your seat?

Hi Everyone

My current bike configuration has 172.5mm cranks.

If I reduce my crank length to 170mm, would that mean lowering the seat by 2.5mm or 5mm?
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Old 03-11-10, 06:05 AM   #2
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You should be able to raise the seat.
The measurement saddle-to-pedalstroke-bottom will reduce by 2.5mm.
Seat should be able to come up that amount.
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Old 03-11-10, 06:59 AM   #3
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Quote:
Originally Posted by Metzinger View Post
You should be able to raise the seat.
The measurement saddle-to-pedalstroke-bottom will reduce by 2.5mm.
Seat should be able to come up that amount.
I'm not sure that I follow.
If my crankarms will be shorter, I will therefore be lower to ground - 2.5mm so to speak. If I want to keep the same pedal-to-seat length ration, would I not be lowering my seat?
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Old 03-11-10, 07:41 AM   #4
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When trying to picture a mechanical relationship, it helps to imagine extremes.
Picture:
a: cranks so long they hit the ground. It's hard to reach the pedals because they're on the ground at full extension. Lower your saddle so you can reach those distant pedals.
b: 1cm cranks. It's easy to reach the pedals because they're basically at the level of the bottom bracket. Raise your saddle so you can extend your leg more.
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Old 03-11-10, 07:49 AM   #5
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Quote:
Originally Posted by Metzinger View Post
When trying to picture a mechanical relationship, it helps to imagine extremes.
Picture:
a: cranks so long they hit the ground. It's hard to reach the pedals because they're on the ground at full extension. Lower your saddle so you can reach those distant pedals.
b: 1cm cranks. It's easy to reach the pedals because they're basically at the level of the bottom bracket. Raise your saddle so you can extend your leg more.
Yes! You're right, because you're measuring from the bottom of the stroke.
I'm so glad there are smarter people out there than me.
Thanks!
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Old 03-11-10, 03:47 PM   #6
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You lost?
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