what is the difference between a short/medium cage rear derailleur and a long cage r.d.?
im planning to buy a Deore LX r.d.,to upgrade my acera r.d., would a long cage rd be good enough for trail riding?
The cage length affects capacity. Capacity is defined as the difference between the number of teeth on the largest and smallest cogs, added to the difference between the number of teeth on the big chainring and the small chainring. Long cage rear derailleurs have a high capacity, and can therefore handle a very wide range drivetrain. Short cage rear derailleurs are more limited in their capacity, working best on a drivetrain with closer gearing.
Shorter cage rear derailleurs take up less chain slack than a long cage rear derailleur. The chain is held more snugly, which can result in smoother, more precise shifting. However, longer cage rear derailleurs are capable of taking up more chain slack than a short cage rear derailleur, allowing you to run a wider range drivetrain than would be possible with a short cage rear derailleur.
For road bikes, your choice is fairly straightforward. If you plan to use a double crankset, stick to a short cage unit. For triple cranksets, you’ll want to use a longer cage rear derailleur to handle the increased chain wrap necessitated by the wider range drivetrain.
On a mountain bike, your choice is slightly more difficult. Less experienced riders, or riders who ride frequently in steep terrain should probably stick to a long cage rear derailleur. This, combined with proper chain length, will allow the bike to be safely shifted into every gear on the bike. Racers might appreciate the lighter weight and slight shifting improvement a short cage rear derailleur offers. However, these benefits come with a tradeoff – because of the decreased capacity a short or medium cage rear derailleur offers, it may not be possible to safely use the small chainring in tandem with the smallest cogs. (The derailleur simply can’t take up enough slack in the chain)
For mountain bikes, when in doubt, choose a long cage rear derailleur, unless you are certain you understand the limitations of a short/medium cage derailleur.
Build a Bike with Greenfish:Part 2
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