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Just had my bike fit session using the "bike fitting system".

Aside from the other changes i've had to do, move my saddle forward so as to achieve the proper plumb line and lengthen my stem so the over all reach is corrected, they also recommend that I use a 170 crank arm lenght instead of my current 172.5 mm.

Will this make a big difference?
 

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grnhrnt said:
Just had my bike fit session using the "bike fitting system".

Aside from the other changes i've had to do, move my saddle forward so as to achieve the proper plumb line and lengthen my stem so the over all reach is corrected, they also recommend that I use a 170 crank arm lenght instead of my current 172.5 mm.

Will this make a big difference?

Its a difference of 2.5mm per crank arm. 172.5 - 170 = 2.5mm

Hope this helps.
 

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"Crank Length

The right crank length, like any other part of fitting a bike, boils down to body size and riding style. Longer cranks provide more leverage for pushing large gears at a low cadence in climbing, time trialing, and the like. Riders who sprint or otherwise use a high cadence will do better with standard crank sizes.

Longer cranks tend to cause a sharp bend in the knees at top dead center, right when power begins to be applied. Cranks that are too short won't be as efficient, as sticking to higher cadences involve the leg mass moving around more than with a shorter crank.

For general road racing and touring, those with road frames smaller than 21" (54 cm), or people less than 5'9", will want a 170 mm crank. Frames from 21.5" to 24" (55 to 61 cm), people from 5'9" to 6'1", will probably want cranks from 170 to 172.5 mm. Those with frames over 24.5", typically over 6'2", tend to want cranks of 172.5 to 175 mm. Be sure to read our article about your optimal frame size.

The story isn't over, of course. If you are a track races, reduce this estimate by 2.5 mm, more if the races are short or the track is steep. If you have frequent knee problems, shorten the cranks by 2.5 to 5 mm, and adjust your gear choices downwards to reduce the stresses your knees have to endure from mashing a crank with more resistance.

If you're calculating this to use an a mountain bike, use cranks 2.5 to 5 mm longer than on a comparable road bike. If you ride time trials or hilly races, add 2.5 mm to your crank. For pure hill climbs, add 5 mm."

Source http://www.bicyclesource.com/bike/fitting/crank-length.shtml
 

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grnhrnt said:
Just had my bike fit session using the "bike fitting system".

Aside from the other changes i've had to do, move my saddle forward so as to achieve the proper plumb line and lengthen my stem so the over all reach is corrected, they also recommend that I use a 170 crank arm lenght instead of my current 172.5 mm.

Will this make a big difference?
How tall are you? 4'11"? 5'3"?
 
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