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Discussion Starter · #1 · (Edited)
I'm currently riding Shimano Ultegra 170 mm cranks. Am wondering if moving to 165mm cranks would be any beneficial (performance and efficiency-wise). Would I notice any difference at all? My height is 5'5" with an inseam of 30", and my riding style is serious recreational.

Any helpful advice is greatly appreciated.
 

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While there's tons of speculation out there, there's nothing out there proving that a change in crank length can increase overall performance (= speed) or efficiency. If you've been comfortable with the 170s, stay with them.

There is one situation in which shorter cranks could make sense. If you prefer your saddle relatively low and you feel a bit scrunched up at top dead center of the crank circle, a shorter crank would give your thighs more "breathing room" in relation to your upper body. Installing a 5 mm shorter crank and raising your saddle and handlebar 5 mm to accomodate that change would give you 5 + 5 = 10 mm more space between your thigh at top dead center and your upper body. Doesn't sound like much, but if you're at your limit of a comfortable thigh angle, it is.

/w
 

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The only reason a person needs 165's is if they have them on a track bike, and will be spinning 125/150 rpm's at the end of their races.

170's (or even 172.5's) would be fine for you.
 

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Generally spinners prefer turning the smaller circle of short cranks, and low rpm power riders prefer longer cranks. Otherwise, there's little hard data to support the conclusion that crank length affects performance either way, as long is it's within a usable range for the rider.

While taller riders can easily turn shorter cranks, overly long cranks are a handicap for short riders, bringing their knees too high at the top of the stroke, and/or forcing them to reach for the pedals at the bottom. That's why children's bikes use shorter cranks, but where that comes into play for adults is a judgment call.

If you have short legs, (say, 24" inseam or less) and can't find a seat height adjustment allowing you to pedal smoothly without that feeling of bringing your knees up to your gut, shorter cranks will help, otherwise don't expect any meaningful change.
 

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BikeFixer said:
Also, the shorter length will give less leverage
Yes, but the shorter crank has a smaller crank circle. So at the same leg speed, you'll have completed a crank revolution quicker than you would have with longer cranks, making up for the "less leverage." People often say "shorter cranks allow you to spin better." But again, that's just because you're done with one revolution a little earlier than you would be with longer cranks. You can spin a long crank just as well as you can a short one, but you have to increase your leg speed to do so.
 

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iamddn said:
funny - I have a 30" inseam and I want to go from 170mm to a 175mm crank for more leverage.
Grinding up a hill at a cadence of 60, that "longer leverage" may actually be of some use, as it would be for trundling down to the pub on a black, fendered coaster brake bike at 6 mph and a cadence of 30. But if you're talking about fast riding, you need to make lots of power, which is the rate at which work is performed. So while "leverage" is part of the equation, it's not going to get you much unless you team it up with leg speed. You could say that "leverage" is good for pedal pumpers, but is not the answer for riders who want to produce large amounts of power with the appropriate combination of pedal force and crank velocity.
 

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5’5”, 29cm inseam. I’ve got 165mm cranks on my road bike. I’ve also got 172.5mm cranks on another bike. Can’t tell the difference.

I only got it because it was an Ultegra crankset on Nashbar, about 2 years ago.
 

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3v1lD4v3 said:
I've been riding on 165mm Sugino XD600. It's fine when I'm seated and spinning, but I can feel the difference from my 170mm Trek when standing. Doesn't feel like a long enough stroke.

FWIW, I'm 5'6" with a 31" PBH.
It's very difficult to turn high cadences out of the saddle. But with enough training, it can be done—as evidenced by L. Armstrong in his finest years. I'm convinced it took a grueling training regimen to get him to be able to do that.
 

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wim said:
It's very difficult to turn high cadences out of the saddle. But with enough training, it can be done—as evidenced by L. Armstrong in his finest years. I'm convinced it took a grueling training regimen to get him to be able to do that.
I can do 85 rpm while standing, it's the lower grunting that feels too short. Lower RPMs in general don't really do it for me anymore.
 
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