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I'm 5'11 1/2". My inseam is 32". Currently on the roadbike I have 170mm cranks. I would like to move up to 172.5 for the leverage. Any problem with that? How about 175 as that is what is on the mtb?
 

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No problem

RetroG said:
I'm 5'11 1/2". My inseam is 32". Currently on the roadbike I have 170mm cranks. I would like to move up to 172.5 for the leverage. Any problem with that? How about 175 as that is what is on the mtb?
Road cranks usually have slightly shorter crankarms than MTB cranks to facilitiate spinning and because there isn't as great a need for leverage as there is on a MTB. Are you a spinner or a masher on the road? Do you have knee problems? If you like to spin and/or have knee problems stick with 172.5. If you like to mash and knee's aren't an issue 175's could work. Neither choice is likely to make a huge difference.
 

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Go for the 172.5's

RetroG said:
I'm 5'11 1/2". My inseam is 32". Currently on the roadbike I have 170mm cranks. I would like to move up to 172.5 for the leverage. Any problem with that? How about 175 as that is what is on the mtb?
I to had 170's on the roadie. With the shorter cranksarms it felt harder to stay on top of a tall gear like i lacked leverage. It also felt like my spin circle ewas to tight. I went to a compact road crankset with 172.5 cranks. It feels alot better.

Leave the 175 for a MTB or CX bike.
 

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I read a test in a magazine (I think it was in the short-lived Road Bike Action) where they had people do a time trial with three different crank lengths. Everyone improved their time with longer cranks.

This, however, doesn't account for personal taste, knee problems, riding style, etc.

TN
 

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Got clearance Clarance?

I went from 170 to 175 crank on my road bike and now I have toe overlap when the cranks are horizontal and my inner pedal hits the ground sooner in a turn.

The toe overlap only happens in slow riding and the pedal gound strikes only happen at high cornering speeds. My bike is very short coupled. You can see what I mean from the pic.
 

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I'm not suprised, however shorter cranks should allow you to spin more smoothly in a lower gear.

Long term, this would be better on the knees and hips. Also the guy who takes the spinning classes at my gym (semi pro roadie) says that research shows that you recover faster if you spin a lower gear as opposed to mashing a big gear.
 

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Discussion Starter · #7 ·
I would think...

Mingsta said:
I'm not suprised, however shorter cranks should allow you to spin more smoothly in a lower gear.

Long term, this would be better on the knees and hips. Also the guy who takes the spinning classes at my gym (semi pro roadie) says that research shows that you recover faster if you spin a lower gear as opposed to mashing a big gear.
the bigger gear would be easier to "mash" with the increased leverage of the longer crank arm.
 

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Funny thing is....

I have 172.5s on my roadie, but both of my MTnbikes have 170mm crankarms. The roadie is a Specialized that I built from the frame up and picked the components myself. The Mtnbikes are Treks 18.5" frames that I purchased as complete bikes. if I were to get the same frame size in a complete bike in the roadie, it would come with 170mm cranks as well. My inseam is the same as yours, but I am much shorter.

I really can hardly tell a difference from one crank to the next. I do notice that my knees will touch the bar with the longer cranks, and they did not with the 170mm cranks that I started with on the roadie.
 

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I think its all a matter of body size/leg power. Thinner guys aren't going to be able to put the same amount of power/torque down, but they go just as fast/faster because they weigh less. I've found that longer cranks feel pretty much the same on flat ground or downhills, but going up hill where they feel better. (FWIW Im a bigger guy and I push uphill in big gears fairly slow rpms)
 
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