Runge
03-09-02, 08:04 PM
Whats the differnce?
Do both work on the same bike or long works on some and medium works on other bikes?
Do both work on the same bike or long works on some and medium works on other bikes?
Bicycle Mechanics - Difference between long cage and medium cage rear derailers
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John E
03-09-02, 09:00 PM
The difference is chain wrap, or tooth capacity, which you can compute by adding the difference between your largest and smallest chainrings to the difference between your largest and smallest freewheel/hub cogs.
Mountain bikes almost always need long cages, whereas some road touring bikes can get by with medium cages, and road racing bikes often have short cages. A longer cage will offer superior control over chain tension from gear to gear, but at the price of weight and flopping over bumps.
Real-world examples:
1) My mountain bike, 48-40-24 / 13-26. Total takeup capacity required = (48-24)+(26-13) = 37T, which pushes my long-caged 1988 SunTour XC derailleur about to its limit. Since I never use the large-large and small-small combinations, it works fine and actually has to deal with a range of only 48+24-(24+15) = 33T.
2) One of my commuting/transportation road bikes, 48-45-34 / 13-24. This mid-range half-step-plus-grannie requires a capacity of 25T, which my short-cage SunTour Cyclone derailleur can barely handle, particularly again since I avoid cross-chaining and actually need a capacity of (48+21)-(34+15) = 20T. Typical contemporary Tour de France gearing, 53-39 / 11-21, puts a comparable load on the takeup spring.
Mountain bikes almost always need long cages, whereas some road touring bikes can get by with medium cages, and road racing bikes often have short cages. A longer cage will offer superior control over chain tension from gear to gear, but at the price of weight and flopping over bumps.
Real-world examples:
1) My mountain bike, 48-40-24 / 13-26. Total takeup capacity required = (48-24)+(26-13) = 37T, which pushes my long-caged 1988 SunTour XC derailleur about to its limit. Since I never use the large-large and small-small combinations, it works fine and actually has to deal with a range of only 48+24-(24+15) = 33T.
2) One of my commuting/transportation road bikes, 48-45-34 / 13-24. This mid-range half-step-plus-grannie requires a capacity of 25T, which my short-cage SunTour Cyclone derailleur can barely handle, particularly again since I avoid cross-chaining and actually need a capacity of (48+21)-(34+15) = 20T. Typical contemporary Tour de France gearing, 53-39 / 11-21, puts a comparable load on the takeup spring.
Runge
03-09-02, 09:13 PM
ok. I have
22-32-44/11-32
So I have 43T.
What would I need?
22-32-44/11-32
So I have 43T.
What would I need?
John E
03-09-02, 09:29 PM
A very long cage.
RainmanP
03-10-02, 05:50 AM
I have found the Shimano Deore XT rear der, which has a capacity of 45T, to be a very well made and reliable derailleur. Performancebike.com has them on sale for $39.95 right now.
Runge
03-10-02, 10:41 AM
So your saying you cant use a XTR crank(24/34/46t) with a xtr back freewheel/cogs? they equal up to around 43-45T.