Mechanics of switching to compact

Discuss light weight issues concerning road bikes & parts.
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psycling
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Joined: Tue Jan 13, 2009 3:30 pm
Location: Mountain View, CA

by psycling

I have made the decision to switch from a standard crankset (53/39) to a compact (50/34). I am currently running all Dura Ace 7900. I just ordered a new FC-7950 crankset. What will be involved in making the switch? Is this just a matter of swapping out the cranks? Or will the 50T chainring require that I lower the front derailleur to maintain proper tolerances? Also, will I need to shorten the chain with this change? Thanks!

by Weenie


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btompkins0112
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Location: Mississippi

by btompkins0112

Yes and yes. Lower derailleur and shorten chain.....

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sugarkane
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by sugarkane

But.....
You if ou want it too shift well you need to set the cage to big ring gap towards the upper limit not the lower limit like you would with a std chain set.

Basically It needs a little more room to get the chain up nice and fast. Between 2-3mm works pretty good in my experience

daj
Posts: 246
Joined: Mon Oct 12, 2009 6:36 pm

by daj

No need to shorten the chain. I switch between compact and regular crankset 2-3 times a year, never changed the chain length and never had any problems.

bm0p700f
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by bm0p700f

I think the above will be true if your cassette is of narrow range. The wider the range of the cassette the more likely you will encounter chain length issues.

psycling
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Joined: Tue Jan 13, 2009 3:30 pm
Location: Mountain View, CA

by psycling

I'm running an 11-28 cassette. It would certainly be nice to be able to easily switch between compact and standard. I guess I'll just wait and see how things look as I do the install.

by Weenie


aaric
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Joined: Thu Jun 09, 2011 4:10 pm

by aaric

there's two schools of thought for optimal chain length:

1) minimum length: You wrap big-big, and then add 2 lengths. This gets you the lightest weight. However, to switch gearing, you end up needing a new chain if you need more links, since piecing together links of a chain with different amounts of wear can cause issues.

2) maximum length: You go small-small, and thread it through the derailleurs, then subtract the least amount of lengths to get to a length the derailleur can handle. This sacrifices some weight, but allows the greatest amount of adjustability in gearing. It probably makes your chain last slightly longer since the wear is distributed across more links.

Personally, I tinker with my gearing a reasonable amount, so I go for maximum length at the expense of 10-15 grams.

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