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  1. #1
    Member Ramfactor's Avatar
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    155 mm crank on comfort bike?

    I hope someone can help me. I'm trying to find shorter crank arms for my comfort bike. I'm 5'3" and current cranks are 170mm. I've been having a lot of knee pain and it has been suggested that a shorter crank may help. My current setup is a Shimano FC-M191, 28/38/48 teeth crankset. Problem is that this right crank arm has 4 spindles (for lack of a better word) and all the after market arms I'm finding have 5. Does anyone know where I can get 155 or 160 mm crank arms that will work or will I need to replace the whole crankset?
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  2. #2
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    Contact Terry Precision Bicycles. They used to market shorter cranks intended for shorter people.
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    The 'spindles' are the 'arms' of the 'spider.' 4 arm spiders are very common, but perhaps not in the length you like. No matter, though, it is usually not any (much) addisitonal cost to buy a crankset with rings.

    BTW, are you sure the length of the cranks is causing the pain? The two most common causes of knee pain from cycling are riding in too high a gear, and riding with the saddle too low.

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    At 5'3" the OP probably would benefit from shorter cranks. At that height the difference in height at 12 vs 6 o'clock is so great that what's too high for the bottom of the stroke will also be too low for the top.

    Odds are the OP will need a complete new crankset, but as LarDasse pointed out that's no issue, because since complete crank sets are usually cheaper than left and right arms bought separately. (they charge extra for removing those pesky chainrings).
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  5. #5
    Senior Member Shimagnolo's Avatar
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  6. #6
    Member Ramfactor's Avatar
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    Quote Originally Posted by DCB0 View Post
    The 'spindles' are the 'arms' of the 'spider.' 4 arm spiders are very common, but perhaps not in the length you like. No matter, though, it is usually not any (much) addisitonal cost to buy a crankset with rings.

    BTW, are you sure the length of the cranks is causing the pain? The two most common causes of knee pain from cycling are riding in too high a gear, and riding with the saddle too low.
    So what do I need to know before ordering a crankset with rings? I want to be sure it will fit. The only info I have about my BB says "TH Cartridge". Also, I try to stay in a lower gear and keep my cadence up and yes, I've been through the seat height trials. I really think the problem is my short legs. lol!
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    Quote Originally Posted by Ramfactor View Post
    So what do I need to know before ordering a crankset with rings? I want to be sure it will fit. The only info I have about my BB says "TH Cartridge". Also, I try to stay in a lower gear and keep my cadence up and yes, I've been through the seat height trials. I really think the problem is my short legs. lol!
    I just wanted to make sure you had covered all your bases. My wife is 5'3 and she rides with 170s, but everyone is different.

    It is likely that you have a 'square taper' bottom bracket spindle (this is the correct use of that word). You need to find a crankset that requires a square taper bottom bracket with the same or similar spindle length. If your bb is an odd size, replacements bbs are ~$10 or $15, and you can sell your old crankset with the original bb as a set.

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    There's this guy too. He may be able to shorten your existing cranks for you. Whether it'll make financial sense or not I can't tell, but it may still be the least-hassle option. No question about fit to the BB anyhow...

    You may want to look at the Q-factor (sideways spacing between pedals) as well. There are a few people who do better with wider cranksets. You can get pedal axle extenders, do a net search for knee savers and you'll find some.
    Last edited by dabac; 12-02-11 at 02:21 AM.

  9. #9
    Member Ramfactor's Avatar
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    Quote Originally Posted by dabac View Post
    There's this guy too. He may be able to shorten your existing cranks for you. Whether it'll make financial sense or not I can't tell, but it may still be the least-hassle option. No question about fit to the BB anyhow...

    You may want to look at the Q-factor (sideways spacing between pedals) as well. There are a few people who do better with wider cranksets. You can get pedal axle extenders, do a net search for knee savers and you'll find some.
    Thanks, I am considering this option, but 170 mm becomes 148 and I'm afraid that may be too short. I guess I could buy some 175's, the have them shortened to 153. Thanks for the help!
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  10. #10
    pmt
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    It's pretty easy to get them on eBay brand new for doubles. You'll end up with a five-bolt 110, but a 34/44 would be a good setup.

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