Gear skipping problem, cause?

pete1336

Hi all.
My son's bike is a Boardman Road team sport. It has an eight speed cassette. Recently I noticed that whilst cycling, the gears will skip by themselves as if I'm trying to change gear. This caused me to check for chain wear and using a specific chain wear tool I noted that the chain had indeed stretched to an amount where changing the chain was recommended. When the new chain was on I noted that the skipping problem, whilst out riding was still present. I checked the indexing beforehand and believe that's fine...the skipping problem doesn't happen whilst the bike is on the stand and I'm running the chain up and down the cassette.
Someone suggested the skipping problem might be caused by the cassette itself, as components can wear out together. Well I checked the cassette, the teeth look fine on each cog and with the back brake deployed and pedal depressed, there is no slippage or movement of the chain over the cassette teeth.
So my question then is this...assuming the skipping problem is not caused by poor indexing and the cassette is not worn...what else can be causing the skipping?
Thanks all.
Pete.

clickrumble

Check that everything that should be tight is; shifters clamp on handlebars, cable clamp, derailleur hanger screws and attachment bolt. Also check the cassette retaining ring is tightened up correctly. Check derailleur hanger alignment.

wishitwasallflat

What you describe is exactly what happens if the cassette wears too far - they do work, with the chain they wore with, but skip with a new one. Ive read on here that it can settle down after a few miles if its not too bad but I would worry myself if it did that it would wear or stress the chain unduly. I would get a new cassette.

The Rookie

As above, its likely the cassette has worn, it won't always be obvious as the wear can be subtle. Have you/he noted which gears it does it?

Also check for dirt/debris trapped between the cassette sprockets that can lift the chain off the teeth.

It can also be the freehub jumping occasionally but that would tend to only do it in the lower gears (bigger sprockets) as they create more torque at the freehub.

keef66

Stiff link in the chain? Bent derailleur hanger?

You can't tell a worn cassette by looking at it these days; tooth shape has been optimised for smooth shifting, but seemingly at the expense of longevity. It only takes a very subtle amount of wear before a new chain will start riding up the teeth of the most frequently used sprockets and skipping under power.

But you describe it sounding like an indexing problem? Does it happen in a particular gear? Only after changing up the cassette or down? In both chainrings? Can you ride behind the bike while your son is riding it and watch what happens out on the road?

pete1336

Many thanks all for your helpful replies. I ended up ordering a new cassette, going to fit it this afternoon, fingers crossed.

ben-----

Also check direction of chain, if it's a directional one. I think some/all? Shimanos are directional, some/all? KMCs not.

milemuncher1

If you change a chain, without changing cassette at the same time, you will tend to find a bit of skipping occurs. The chain and cassette tend to 'mesh' in a certain way, like a handshake. Putting a new chain on an old cassette leads to a few miles where the 'handshake' hasn't occurred. After a few miles, the chain and cassette will eventually mesh, but there will be undue wear put on the new chain in the process, and it may not last as long as it could. I always play it safe and replace chain and cassettes together.

Bobbinogs

Milemuncher1 wrote:

... I always play it safe and replace chain and cassettes together.

Blimey, that must be a lot of decent metal going into the bin. I get through a chain every 6 months replacing at the 0.75 point and only bother changing the cassette about every ~4 chains, sometimes even 6. Still, there seems to be a good deal of subjectivity in this area.

wishitwasallflat

Bobbinogs wrote:

Milemuncher1 wrote:

... I always play it safe and replace chain and cassettes together.

Blimey, that must be a lot of decent metal going into the bin. I get through a chain every 6 months replacing at the 0.75 point and only bother changing the cassette about every ~4 chains, sometimes even 6. Still, there seems to be a good deal of subjectivity in this area.

+1 to this i run minimum four chains per cassette (all weather riding) but reckon thats conservative and I could get more

keezx

Milemuncher1 wrote:

If you change a chain, without changing cassette at the same time, you will tend to find a bit of skipping occurs. The chain and cassette tend to 'mesh' in a certain way, like a handshake. Putting a new chain on an old cassette leads to a few miles where the 'handshake' hasn't occurred. After a few miles, the chain and cassette will eventually mesh, but there will be undue wear put on the new chain in the process, and it may not last as long as it could. I always play it safe and replace chain and cassettes together.

A few remarks about this:
The matching of an old cassette and new chain only takes place by elongating/wear of the new chain and this can take several hundreds of miles.
A new chain will not wear prematurely by putting it on a allready worn cassette. it just wears by using it.

milemuncher1

Bobbinogs wrote:

Milemuncher1 wrote:

... I always play it safe and replace chain and cassettes together.

Blimey, that must be a lot of decent metal going into the bin. I get through a chain every 6 months replacing at the 0.75 point and only bother changing the cassette about every ~4 chains, sometimes even 6. Still, there seems to be a good deal of subjectivity in this area.

That's true, but I use the chain / cassette change, as an excuse to explore new ratios / fancy blingy chain tech.

milemuncher1

Keezx wrote:

Milemuncher1 wrote:

If you change a chain, without changing cassette at the same time, you will tend to find a bit of skipping occurs. The chain and cassette tend to 'mesh' in a certain way, like a handshake. Putting a new chain on an old cassette leads to a few miles where the 'handshake' hasn't occurred. After a few miles, the chain and cassette will eventually mesh, but there will be undue wear put on the new chain in the process, and it may not last as long as it could. I always play it safe and replace chain and cassettes together.

A few remarks about this:
The matching of an old cassette and new chain only takes place by elongating/wear of the new chain and this can take several hundreds of miles.
A new chain will not wear prematurely by putting it on a allready worn cassette. it just wears by using it.

Did you read that before you posted it?

keef66

In the good old days of my 5 speed racer everything was made of steel, and the teeth on chainrings and sprockets were great big gnarly things. Nothing ever seemed to wear out.

Nowadays the sprockets are thinner, and the teeth are shorter and often extensively machined to produce smooth shifting, which is nice, but I suspect it means they are less tolerant of wear.

I tend to replace chains when they get to 0.75% wear, and cassettes only if a new chain starts skipping and doesn't settle down. Some cassettes last years. And I do like a shiny new chain! I don't necessarily do it because that's the cheapest way; I'm sure I'm chucking a lot of functional chains in the recycling bin.

The alternative is to run everything into the ground, and wear out chain, cassette and chainrings together. Which is effectively what I did on my MTB which was still functioning after 10 years when it was finally nicked. And after 10 years, technology had moved on so 8 speed replacements would have been cheap...

pete1336

Finally got around to taking the new cassette out for a test ride today. All seemed to go well and hopefully fitting the new cassette has solved my problem. Thanks to everybody for your help.

milemuncher1

pete1336 wrote:

Finally got around to taking the new cassette out for a test ride today. All seemed to go well and hopefully fitting the new cassette has solved my problem. Thanks to everybody for your help.

Marvellous, happy to help.