Support road.cc

Like this site? Help us to make it better.

Skipping under load with new chain and cassette

I'm riding an 09 Genesis Vapour, original short cage 105 rear mech, Sora compact. I've been using it as a wet weather bike/commuter with a 25-12 cassette, but when I wrecked my MTB recently I put the Cross tyres back on and changed the cassette to a Shimano 28-12 so I could go XC on some steeper tracks.

The existing chain (2 months old, not worn) skipped a bit on a few gears, so I replaced it, but no joy. Now the cassette and chain both have about 20km on them. While the highest and lowest gears are fine, all the gears in the middle of the range skip badly under load. I've replaced the rear gear cable, stripped and cleaned the rear mech jockey wheels and as far as I can tell, the indexing is OK and if I put the old 25-12 cassette back on the problem goes away, even with the new chain.

My thinking is that the 105 short cage mech can't handle 28-12, even though it has no problem in getting to the innermost cog. However the guy in the (Edinburgh Bike Co-op) shop reckoned it would be fine, but the 32-12 wouldn't. This seems to be the common reasoning elsewhere too.

Any suggestions as to what to try next? Chain length? Derailleur hanger angle adjustment? New jockey wheels?

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

Add new comment

7 comments

Avatar
arrieredupeleton | 12 years ago
0 likes

Glad it worked out for you Gordon. Looks a nice bike that Genesis.

Avatar
Gordon Watt | 12 years ago
0 likes

Yay! B-screw loosened a couple of turns and all is good in 28-12 world. Thanks for the suggestion...

Avatar
Gordon Watt | 12 years ago
0 likes

Genius - thanks for that. I'll have a go this evening but that makes a lot of sense...

Avatar
arrieredupeleton | 12 years ago
0 likes

Apologies if this is stating the obvious but have you considered the 'B-screw'? The upper pulley needs to track the cogs of cassette as close as possible and if you have a widely spread cassette there will be a wider gap in the middle compared to the extremes (12 and 28?) at each end. Think of it as a concave section. I've had a similar issue with a 11-28 Ultegra cassette I bastardised.

Avatar
stuke | 12 years ago
0 likes

What condition are your chainrings in? i had the same issue after replacing chain and cassette a couple of years ago on one of my bikes, it only happened in the big ring though. I replaced the chainring as the teeth were pretty worn and it fixed the problem straight away.
jockey wheels could be worn and leading to this problem also

Avatar
Gordon Watt | 12 years ago
0 likes

When I put the new cable on I removed cleaned out the barrel adjuster and reset the indexing from scratch, so I don't think that's it.

Avatar
stewieatb | 12 years ago
0 likes

Hmm. Have you tried re-indexing the mech from scratch? Odd that it's the middle range that's going wrong.

Latest Comments