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So my chain is slipping in the top 3 gears but only when applying a lot of pressure. My initial assumption is the chain is not tensioned enough and I may need to change the rear dérailleur to achieve the correct tension.
My current set up is 2x10 with a new chain and new ish cassette (11x40 sun race) I think its a short dérailleur which may not be giving me enough tension for the length of chain required for a 2x10 set up?
Any ideas or advice appreciated
Most likely the cassette is worn, or the teeth are a little shark finned.
Recommend.... New Cassette, before the chain wears further.
The only other thing I can think of is the b-tension screw could be a little too far out, check to see if the high jockey wheel is clearing the cassette when in the top 3 gears, should have about a 5mm gap there.
More details needed,
is this a new build/parts that you have put together,
or has it all worked together in the past and is not any more?
worn cassette with new chain
Tension as supplied by the derailleur is only to keep the unused portion of the chain from flopping around in high gears. It doen't have any affect on the portion of chain between the two (front and back) gears, so don't go spending money on new derailleur just yet and don't mess with the body screw either.
If you changed the chain and the cassette is not that old - try putting the old chain on and seeing if it skips - then it's likely that the new chain is skipping off the teeth on the front rings.
The cassette is about 50 miles old, will check b screw.
Its parts I have put together
If it's not the cassette it's likely the new chain on worn chainring.
Just had same thing on my road bike. Only jumped under heavy pressure, like a snap of acceleration.
After all the stuff listed above, start looking for the odd ball stuff. Could it be a stiff link in the new chain that only binds at extreme angles? Mate of mine struggled with similar, only to discover that the master link was twisted.
I would have thought that a short cage rear mech is not going to be up to running a 2x with an 11-40 casette .
Daft question - did you shorten the new chain to match the old one? Have you checked the length?
Ramsey your spot on, using this:
Working it out:
[ Largest Front Ring - Smallest Front Ring ] + [ Largest Rear Ring - Smallest Rear Ring ] = Required Capacity
[ 38 - 24 ] + [ 40 - 11 ] = 43T
SRAM
Long = 45T
Medium = 37T
Short = 30T
So I think I have a short of medium cage and need a long in order to maintain the correct tension!
Thanks Guys - now i need to find a new dérailleur and possibly add some links back in to the chain (hopefully not)
So I think I have a short of medium cage and need a long in order to maintain the correct tension!
Your chain doesn’t skip because of a lack of tension, it’s skips because it can’t hold onto the gears. The chain is only in operation between the top (well, top and back a bit) of the front ring and the top of the cassette sprocket - that’s where all the effective/working tension is. The tension created by the derailleur is to take up the slack *under* the gears, the slack (excess chain) required to allow the chain to fit around your both the smallest and the largest gear combinations - the wider the range of gears, the more chain you need, and the longer the derailleur cage needs to be to accommodate it. Derailleur tension stops the chain from flapping around, stops it coming off (laterally) if you backpedal, but doesn’t cause or prevent the chain from jumping vertically off the gears, which is what skipping is. A stuck link, damaged chain, or worn chain/gears are the causes of skipping.