Intermittently rough gears...

[Andy in Germany]

On a number of bikes where I've been setting the gears, I noticed a couple of minor but annoying issues, mainly a "rough" feeling in one or two random gears, as if the mech is slightly off. There's no visible reason for this, and it only happens in specific gears; often it's the larger cogs in the rear cassette. Do other people experience this, and what causes have you found?
It seems to happen in differenc bikes so I'm aware it may be a won chain or gears...

 

[si_c]

On a number of bikes where I've been setting the gears, I noticed a couple of minor but annoying issues, mainly a "rough" feeling in one or two random gears, as if the mech is slightly off. There's no visible reason for this, and it only happens in specific gears; often it's the larger cogs in the rear cassette. Do other people experience this, and what causes have you found?
It seems to happen in differenc bikes so I'm aware it may be a won chain or gears...

Most likely slightly bent derailleur hanger. As the cage moves over the bend becomes more exaggerated compared to the smaller sprockets.

 

[Grant Fondo]

On a number of bikes where I've been setting the gears, I noticed a couple of minor but annoying issues, mainly a "rough" feeling in one or two random gears, as if the mech is slightly off. There's no visible reason for this, and it only happens in specific gears; often it's the larger cogs in the rear cassette. Do other people experience this, and what causes have you found?
It seems to happen in differenc bikes so I'm aware it may be a won chain or gears...

I'm scratching my head over a similar issue, but its ONLY on the 4th smallest cog! No sign of damage, but wondering if the cassette lock-ring needs tightening, almost feels like the cog is engaged properly but is rotating if that's even possible? Will whip it off later for a better look.

 

[Deleted member 1258]

On a number of bikes where I've been setting the gears, I noticed a couple of minor but annoying issues, mainly a "rough" feeling in one or two random gears, as if the mech is slightly off. There's no visible reason for this, and it only happens in specific gears; often it's the larger cogs in the rear cassette. Do other people experience this, and what causes have you found?
It seems to happen in differenc bikes so I'm aware it may be a won chain or gears...

I've come across this occasionaly in the past but I've not yet worked out why or a solution to it, got the middle and one end of the cassette changing sweetly and the other end is rough.

 

[Once a Wheeler]

On occasions I have experienced problems because the spacing between two adjacent sprockets varies at different points around the circumferance of the sprockets. The best way to check this is with a gap guage like the one shown here:

Put the appropriate blade between the spockets, rotate the cassette or freewheel and see if it binds in any particular spot. The image is from a Chinese wholesaler web site and such guages are not common in cycling workshops. I think they are mostly sold as gap guages for welding. Doubtless some exist on eBay and Amazon: be sure to get the thicknesses correct — most such guages are for much smaller (sub-mm) gaps used in engine tuning.

On an old-style freewheel, one can just replace the distorted sprocket. Some of the more up-to-date cassettes may not be so easy to fix.

The problem usually occurred on larger sprockets subjected to unusual strains such as hitting a sudden brick wall slope round a blind bend when on tour and heavily loaded.

Just one of many possibilities; but if you do manage to find one of the guages they can come in useful for setting brakes, specifying chainwheel spacers and other adjustment problems.

 

[Andy in Germany]

Many thanks, a shedload of useful information there, at the very least if we can't find the problem I know it'd possibly simply one of those things, and I now have a few things to check for...

Oddly I have the same problem on my own bike but it comes and goes. Yesterday it felt like I'd poured a bucket of sand over the rear mech, today, it was sweet and silent. I'd not done anything with the bike in the meantime.

Even more strange, it often feels worse straight after cleaning and/or oiling the chain...

 

[T4tomo]

On a number of bikes where I've been setting the gears, I noticed a couple of minor but annoying issues, mainly a "rough" feeling in one or two random gears, as if the mech is slightly off. There's no visible reason for this, and it only happens in specific gears; often it's the larger cogs in the rear cassette. Do other people experience this, and what causes have you found?
It seems to happen in differenc bikes so I'm aware it may be a won chain or gears...

I've come across this occasionaly in the past but I've not yet worked out why or a solution to it, got the middle and one end of the cassette changing sweetly and the other end is rough.

Almost certainly a slightly misaligned derailleur hanger.

@Andy if you are running a bike repair business then a hanger alignment tool is essential kit. Not sure if available in Germany but the Wiggle lifeline one works fine and isn't expensive.

 

[8mph]

You can check if your hanger is bent by screwing a spare rear wheel where the mech goes, if it's straight, it should be parallel to your wheel.

Here's a video

 

[Andy in Germany]

Almost certainly a slightly misaligned derailleur hanger.

@Andy if you are running a bike repair business then a hanger alignment tool is essential kit. Not sure if available in Germany but the Wiggle lifeline one works fine and isn't expensive.

We have one; as we're working with used bikes it probably makes sense to make that check part of every refurbishment, just to be sure.