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Left Crank Arms

Old 09-08-22, 02:49 PM
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FREEBIRD1
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Left Crank Arms

Needed to replace a 170 mm one on one of my bikes with the square taper hole, the new parts square hole, is clocked a few degrees off from the original one. I did not notice it when I ordered it, and was unaware there was 2 different types. What do they designate these as so I can be sure to order the correct one?

Thanks.
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Old 09-08-22, 02:58 PM
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There are 2 orientations, diamond and square:


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Old 09-08-22, 03:20 PM
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A 'few degrees off' would be the worn out, 'inside' part of the square taper hole. They're either as above, diamond or square.
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Old 09-08-22, 03:26 PM
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Thanks, I got the "diamond" I needed the "square". On a side note, why do the manufacturers male 2 types? They're actually 45 deg. off.
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Old 09-08-22, 06:46 PM
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Originally Posted by FREEBIRD1 View Post
Thanks, I got the "diamond" I needed the "square". On a side note, why do the manufacturers male 2 types? They're actually 45 deg. off.
They're usually sold in a pair so it doesn't matter. Different manufacturers have decided one style is better than the other, but it probably doesn't really matter.

Note there may be some differences in the "Q-Factor" of the cranks, or the width at the pedals. MTB arms will splay out more than Road arms. Vintage arms can be very straight.

Vintage Campagnolo, Stronglight, and TA could be different from the Asian brands.

But, largely the arms are interchangeable.
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Old 09-09-22, 04:59 AM
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Jax Rhapsody
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i actually didn't know that about square taper
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Old 09-09-22, 09:19 PM
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Originally Posted by Jax Rhapsody View Post
i actually didn't know that about square taper
Me too, regarding diamond vs square orientation.

I guess I always worked with matching cranksets. Anyway, good to know.
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Old 09-10-22, 10:54 AM
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I've been cycling and wrenching for decades and didn't know this.

[the more you know]
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Old 09-11-22, 12:03 AM
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I did know this, or should say learned this, as we replaced quite a few NDS crank arms that were damaged or bent. We now keep the spare left cranks sorted by the orientation.

I try and learn something new everyday.
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