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Crank arms.. crank arms... Headache.

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Crank arms.. crank arms... Headache.

Old 07-17-18, 03:37 PM
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1000Calories
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Crank arms.. crank arms... Headache.

Having a difficult time browsing the web to find the right set of crank arms. I decided to get a new bracket, because the one I got is a tad too long. I currently have a 117mm, but dropping down to a 113mm. Now, after checking out tons of cranksets.. it seems that many of the websites don't specify the manufacturers specs on what bracket size/type it belongs to. My cheap fixie style crankset is meant to be on a 122mm but works fine on a 117. Since I couldn't easily remove it, I mangled it with a hammer because it was stuck on (and I had it greased prior). Finally it came off. So I decided to gravitate towards a crank arm that has bolts for the chain ring, so I don't damage it. Plus it'll be easy to swap chainrings for gear ratio change if anything. So I'm wondering what the average mount size is for most of the arms made. I'm not on a big budget for my bike. So I'm limited to a handful. Any feedback is appreciated. I don't want to have issues with clearance. My new bracket will be a Shimano UN-26 113 JIS.
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Old 07-17-18, 03:42 PM
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Ferrouscious
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The most common BCD's (Bolt Circle Diameter) are probably 110 and 130.
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Old 07-17-18, 03:55 PM
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Originally Posted by 1000Calories View Post
So I'm wondering what the average mount size is for most of the arms made. I'm not on a big budget for my bike. So I'm limited to a handful. Any feedback is appreciated. I don't want to have issues with clearance. My new bracket will be a Shimano UN-26 113 JIS.
It's not quite clear what you're asking, possibly because I don't think you're using some terms correctly. That's not an insult, it just takes time to learn some of this stuff.

I *think* what you are asking is whether your crankset (crank arms refer to the arm parts of the overall crankset) will work with the shorter 113mm bottom bracket spindle.

The reason that spec is not listed is because that depends on your frame, not the crankset. Since it sounds like you have a fixed gear I'm going to assume that any single chainring crankset is probably going to work your frame even with the 113mm spindle.

If not, that's quite possibly the most inexpensive bottom bracket that exists, so if you need to get one with a longer spindle you're not losing much.
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Old 07-17-18, 04:09 PM
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79pmooney
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Get any JIS taper cranks, put them on the BB you got and see how the chainring lines up with the cog. If it is not close, note how much longer/shorter the axle should be (if, say, the chainring should come in 3 mm, buy a BB with an axle 6 mm shorter; the axles are symmetrical).

Probably any BB you look at will be JIS. The other taper is ISO and used by traditional European makers. No harm will happen from using the wrong one, but the crank will not sit anywhere near where you expected it to. All Shimano are JIS. Nearly all Sugino, but not their high end track stuff.

Ben
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Old 07-17-18, 05:50 PM
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It's always worth having the correct tools. They don't have to be expensive - I have a cheap, unbranded crank puller, it cost about a fiver. It's been absolutely essential, it's pulled the most stubborn cranks, some of which had been in place for 30yrs.. I must've used it 100 times.
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Old 07-17-18, 06:00 PM
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1000Calories
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My apologies for the newbie approach. In other words, I've noticed that some crank arms or cranksets may specify that it works with a specific bottom bracket. Some sites would list the JIS or ISO factor and the length of the bracket that it should be paired with. Seems like Amazon is the only place for someone to say that it would work with an (i.e.) 117mm instead of a 122mm BB. That's all.. I really don't know if crank arms are made that much differently and would only work with specific bottom brackets due to clearance and fitment on the taper.

I do have a 68mm threaded shell if you're wondering.
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Old 07-18-18, 08:01 AM
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Here's some good info on bottom brackets to get you started: https://www.sheldonbrown.com/bbsize.html
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