compact crank vs. regular/mix

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2009-07-09 5:48 PM


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Subject: compact crank vs. regular/mix
I have a stock p2 ultegra build which came with the compact crank (50/34).  I am interested in bumping to a 53, do I need to change the smaller one too?  I would like to just change the ring only rather than the entire crank.  Any suggestions??

2009-07-10 12:09 AM
in reply to: #2274451

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Master
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Subject: RE: compact crank vs. regular/mix

Two issues with putting a 53 tooth chainring on a compact crank

1.  The bolt circle diameter is different between compact (110 cm) and regular (130mm).  Most 53T chainrings are 130mm and won't fit on a compact crankarm, but you might be able to find one if you shop around.

2.  The larger difference between the big and small chainrings might cause trouble with shifting.

Probably easier to just switch to a standard crank.  This is a pretty easy change, just make sure you get a crank that's compatible with your bottom bracket, and you'll have to move the front derailleur up a bit.  Or, if you don't have one already, switch to a cassette with an 11 tooth small cog and that will give you a little more top end with the compact crank.

2009-07-10 7:24 AM
in reply to: #2274451

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Subject: RE: compact crank vs. regular/mix
Change both. The front derailleur can't handle the large chainring difference. most can only hanle a 14tooth difference between inner and outer. Compact specific FD's can handle the 16tooth you have now. You're asking to jump to 19 tooth difference between inner and outer rings and that's not going to work.

You CAN find 110mm 53t rings, but by the time you buy both the inner and outer rings, a new cranset becomes more economicqal.
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