rear deraillers

Well, part of the derailleur's job is to take up the slack in the chain when you shift to a smaller cog, either at the front or the back. The length of the cage on the derailleur determines how much slack it is able to take up. If your bike has only two cogs at the front, and the cogs at the rear don't have a wide range (e.g. 11-23), there isn't much slack to be taken up, and you use a short cage. If on the other hand you use a triple chainset, like a 30/39/53, and a wide cassette, like a 12-27, then the amount of slack to be taken up is potentially larger, and you would use a long cage.

The reason the different models are offered is because short cages are marginally lighter than long ones, and some might say they are stiffer and thus offer better shifting performance, although I doubt that's ever a noticeable factor. Short cages are also more aesthetically pleasing to many.

Quoted post said:

Originally posted by mjw_byrne
Well, part of the derailleur's job is to take up the slack in the chain when you shift to a smaller cog, either at the front or the back. The length of the cage on the derailleur determines how much slack it is able to take up. If your bike has only two cogs at the front, and the cogs at the rear don't have a wide range (e.g. 11-23), there isn't much slack to be taken up, and you use a short cage. If on the other hand you use a triple chainset, like a 30/39/53, and a wide cassette, like a 12-27, then the amount of slack to be taken up is potentially larger, and you would use a long cage.

The reason the different models are offered is because short cages are marginally lighter than long ones, and some might say they are stiffer and thus offer better shifting performance, although I doubt that's ever a noticeable factor. Short cages are also more aesthetically pleasing to many.

ya i think stiffness is more a basic function of just general product quality, i know my long cage 8 spd sora dr was flexy enough to really mess up my rear wheel. never had a problem with the 105 long cage dr i replaced it with tho.

Quoted post said:

Originally posted by fushman
......i know my long cage 8 spd sora dr was flexy enough to really mess up my rear wheel.

How do ya do dat?

Quoted post said:

Originally posted by boudreaux
How do ya do dat?

Sounds like a limit screw was out of adjustment and the derailure dove into the spokes no?

limits where fine to my knowledge, i wasnt even in the big cog, just flexed into the spokes and got pulled around :-(

Quoted post said:

Originally posted by fushman
limits where fine to my knowledge, i wasnt even in the big cog, just flexed into the spokes and got pulled around :-(

JRA! Yeah I've heard that before, but it does happen. Strange, I've never heard of a RD flexing that much.

Quoted post said:

Originally posted by KGnagey
JRA! Yeah I've heard that before, but it does happen. Strange, I've never heard of a RD flexing that much.

Right.Something else amiss.

Quoted post said:

Originally posted by boudreaux
Right.Something else amiss.

such as, please redeem sora components in my eyes

Quoted post said:

Originally posted by fushman
such as, please redeem sora components in my eyes

Duno the setup or history ,so I'm not gonna guess. That is just not a 'not stiff enough' RD issue tho.

Quoted post said:

Originally posted by boudreaux
Duno the setup or history ,so I'm not gonna guess. That is just not a 'not stiff enough' RD issue tho.

Yeah, if it wasn't even in the big cog and then suddenly it finds its way into the spokes, something's pretty seriously wrong. I mean, for that to happen purely because the derailleur wasn't stiff enough, it'd have to be made of rubber or something.

Something not many people realise is just how dependent the operation of a RD is on how well it's adjusted. I've got a crappy old rusty steel mtb with a Shimano Tourney rear mech - the very very bottom end of Shimano kit, looks like a piece of Meccano - and it shifts absolutely fine. I've ridden bikes with Deore and even Ultegra drivetrains that didn't shift as sweetly. Granted, the Tourney mech probably won't last very long and will probably need tweaking fairly often, but in fact, pretty much any rear mech by a reputable manufacturer (certainly by Shimano) is going to work just fine, as long as it's adjusted and dialled in properly.

Was there a recent fall to the right side where the RD hanger might have been bent? This would affect shifting pretty bad though and you should have noticed it right away.

The rear derailleur when viewed from the back of the bicycle should be vertically in line with the cogs. My guess is that your rear mech must have bent (even slightly) towards the spokes making it sit dangerously near the spokes when shifted to the biggest cog.

Another possibility is that the fulcrum must have come loose (damaged) and lossening the cage as well.