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Old 09-12-10, 02:37 PM   #1
APER, Man!
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Crank Compatibility Question

Hello!

I have an 80s steel frame Specialized Allez. It's a 12-speed, and I'm hoping to replace the double cranks on the front with a triple crankset. However, I don't know much about bikes, and I'm not sure how to find out which ones are compatible with my bottom bracket. I've attached a picture, but I'm not sure if it'll help. Also, I'd like more than just the answer of which crankset will be compatible. I want to figure out how to determine that.

Here is the info from the triple crankset I was looking at:
Square taper bottom bracket spindles
172.5mm crank arms
130mm BCD
Attached Images
File Type: jpg double_cranks..jpg (102.0 KB, 5 views)
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Old 09-12-10, 02:45 PM   #2
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Get a package of a crankset and a BB .. length of BB is influenced by the design of the crank .
Low Profile = short axle , because of the design of the arm other designs use a longer axle but have the arm
at 90 degrees from the axle , and actually have the pedals further in towards the centerline.. "Q"
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Old 09-12-10, 02:46 PM   #3
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BB shells have not changed for a very long time. Yours has the standard English thread - 68mm width by 1.375 inch. The left side has left hand threads.

http://www.sheldonbrown.com/cribshee...mbrackets.html

You can use just about any triple crank you can find, that uses a threaded BB.
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Old 09-12-10, 02:53 PM   #4
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A triple crank will most often require you to change the rear derailleur to a long cage, get a longer chain, a wider Bottom bracket spindle and a triple compatible front deraileur. if you have downtube shifters instead of STI levers they *should* be able to shift the new front derailleur through all 3 rings.

An alternative is a compact double with an overall lower range of gearing than a traditional racing double. I'm assuming you want to have a lower range of gears. what about your upper range? Are you really spinning out the 53x11 or 12t? How often are you actually in the 53? You can still retain the existing chain and derailleurs in most cases.

A compact double (110 bolt pattern, 48 or 50t outer ring, 34 or 36t inner ring) should give you a reasonable gear range. It will not be as high as a racing dbl, and not as low low as a triple.
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Old 09-12-10, 03:33 PM   #5
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Thanks, everyone. Now I know what I can/can't get, but I'm still unsure as to how you knew. I'm guessing most bikes are the English thread? I have another old road bike I was going to ask about.

Velo-orange, I'm in the 53 quite often. There are some good hills around here with 10% grades. On the way up, it's super hard work. The way down, not so much, but when I do pedal, I'm in the biggest gear ratio.
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Old 09-12-10, 04:28 PM   #6
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We know because the vast majority of frames use English BB threads, except for Italian frames and Eddy Merckx frames for many years.

All you really need to do is measure the BB shell width. If it's 68mm, then it's English. Italian shells are 70mm wide.
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Old 09-12-10, 04:38 PM   #7
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I wouldn't think you'd need a longer chain, unless your triple has larger gears than the double--unlikely, or if you replace the rear derailleur with a longer cage one. You might need a longer or shorter bottom bracket spindle, depending on what cranks you get. Similarly, you might or might not need to replace the derailleurs. Some front derailleurs sold for doubles work fine for triples, in my experience, but I'm sure there are some that wouldn't. Whether or not you need to replace the rear derailleur depends more on the difference between your the number of teeth in your highest and lowest gear. Sometimes, you can get away with not replacing the rear derailleur even though you can't shift into the smallest chainring and the smallest cog at the same time. This is usually O.K., at least for people like me who only use the smallest chainring with the largest three cogs.
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Old 09-13-10, 12:56 AM   #8
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Quote:
Originally Posted by DaveSSS View Post
We know because the vast majority of frames use English BB threads, except for Italian frames and Eddy Merckx frames for many years.

All you really need to do is measure the BB shell width. If it's 68mm, then it's English. Italian shells are 70mm wide.
Thanks, Dave. I like your name, by the way. (I have the same one).


Quote:
Originally Posted by storckm View Post
I wouldn't think you'd need a longer chain, unless your triple has larger gears than the double--unlikely, or if you replace the rear derailleur with a longer cage one. You might need a longer or shorter bottom bracket spindle, depending on what cranks you get. Similarly, you might or might not need to replace the derailleurs. Some front derailleurs sold for doubles work fine for triples, in my experience, but I'm sure there are some that wouldn't. Whether or not you need to replace the rear derailleur depends more on the difference between your the number of teeth in your highest and lowest gear. Sometimes, you can get away with not replacing the rear derailleur even though you can't shift into the smallest chainring and the smallest cog at the same time. This is usually O.K., at least for people like me who only use the smallest chainring with the largest three cogs.
That sounds pretty good. Thank you for the help.
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