(I need....) The definitive idiots guide to gear setup

[Chris71]

Hi,

When adjusting the gears on my bike, I've always relied on a very unscientific method of randomly playing around with the cable and mech settings.

Can someone recommend the best procedure for finding and correcting the cause of slipping gears on a mountain bike? I have to be honest, I'm not always entirely sure what I'm doing when I try it.

In my case, it's a 2003 Sub 5 with Deore bits, but I presume it's fairly universal....

Chris.

[CC07 PEU]

First of all, what do you mean by "slipping gears"?

[pdV6]

^ Wot he said (i.e. are we talking setup or wear?)

For setup see:

http://www.parktool.com/repair/byregion.asp?catid=...

[atom111]

Does it slip in a particular gear whilst under load?

[_daveR]

The Parktool site tells you EVERYTHING you could want to know about bike maintenance.

Chances are its just cable stretch and a setup will sort it. But if the bikes a few years old it may be the cassette/chainrings/chain wearing out.

[Chris71]

It'll select any gear - all extremes, so looking at the Parktools site, it's not the derailure adjustment screws as these only locate the extremes?

It does however slip under load in a few of the gears. I think the adjustment is a bit marginal and it's enough to keep it on the right sprocket for minimal chain tension, but once you start heaving on the cranks, the tension goes up and if it's poorly adjusted the component force pulling to one side will also go up to the point where it drags it off the sprocket momentarily.

Is it likely to be cable stretch?

[threesixty]

If its slipping under load and you've got a good setup then that will be down to drive train wear, which will mean new chain and block.

[CC07 PEU]

threesixty said:

If its slipping under load and you've got a good setup then that will be down to drive train wear, which will mean new chain and block.

Yes, that's what it sounds like to me too, especially if the bike is old and/or has done a lot of miles.

[_daveR]

If you are replacing the chain and rear cogs then really tou should replace the front chainrings too as it will just cause excessive wear on the new parts if you leave the old, worn rings on.

[Chris71]

I think it's setup. The chain and block were replaced not that long ago and there isn't a huge sign of wear.

Like I said, I guess it's well enough setup to engage the desired gear when there's no real load on the chain, but if it's pulling to one side a little due to poor setup, wouldn't the sideways force will be enough to make it skip off the sprocket temporarily under higher load?

[_daveR]

If you did not replace the chainrings (the ones on your cranks) when you replaced the other bits and they are significantly worn too then they will just cause wear to the new components at an accelerated rate. Its not unfeasable for them to have been knackered within a few months or so.

Follow this for setup: http://www.parktool.com/repair/readhowto.asp?id=64

If it still happens after that then Id look for new parts again.

[mk1fan]

Have you checked the chain for a stiff link at all? As this would cause the chain to slip and is easy to check before messing with the gear settings. Although, if you've been messing with the gear settings then they're probably out anyway.

The Park website will give you all the info on set up and adjustment.

[CC07 PEU]

_daveR said:

If you did not replace the chainrings (the ones on your cranks) when you replaced the other bits and they are significantly worn too then they will just cause wear to the new components at an accelerated rate. Its not unfeasable for them to have been knackered within a few months or so.

Nah, worn chainrings won't really cause any wear to a new chain and cassette.

An old chain on new chain rings will cause rapid wear on the chain rings but a new chain on old chain rings will only wear at the normal rate.

Very rarely can you put a new chain on an old cassette and chain rings but often you can get away with a new chain and cassette leaving the old chain rings as they are. I have done this many times and if I have had to buy new chain rings it has mostly been the middle one only.

[CC07 PEU]

Chris71 said:

wouldn't the sideways force will be enough to make it skip off the sprocket temporarily under higher load?

Possibly but it wouldn't skip suddenly, you would hear it sounding as if it wanted to change gear and then it may eventually move to another sprocket and stay there.

Another possibility is that maybe some of the teeth on the sprockets are bent, thus causing the chain to jump about.

[lingus75]

CC07 PEU said:

_daveR said:

If you did not replace the chainrings (the ones on your cranks) when you replaced the other bits and they are significantly worn too then they will just cause wear to the new components at an accelerated rate. Its not unfeasable for them to have been knackered within a few months or so.

Nah, worn chainrings won't really cause any wear to a new chain and cassette.

An old chain on new chain rings will cause rapid wear on the chain rings but a new chain on old chain rings will only wear at the normal rate.

Very rarely can you put a new chain on an old cassette and chain rings but often you can get away with a new chain and cassette leaving the old chain rings as they are. I have done this many times and if I have had to buy new chain rings it has mostly been the middle one only.

Hmmm, I need to do this and have not looked after my drivetrain very weel. Only commute on the bike but I would think clean it all up about once every two or three months. I have an LX chainset with alloy rings so would be surprised if these didn't wear at the same rate? Also, what about jockey wheels?

[CC07 PEU]

lingus75 said:

CC07 PEU said:

_daveR said:

If you did not replace the chainrings (the ones on your cranks) when you replaced the other bits and they are significantly worn too then they will just cause wear to the new components at an accelerated rate. Its not unfeasable for them to have been knackered within a few months or so.

Nah, worn chainrings won't really cause any wear to a new chain and cassette.

An old chain on new chain rings will cause rapid wear on the chain rings but a new chain on old chain rings will only wear at the normal rate.

Very rarely can you put a new chain on an old cassette and chain rings but often you can get away with a new chain and cassette leaving the old chain rings as they are. I have done this many times and if I have had to buy new chain rings it has mostly been the middle one only.

Hmmm, I need to do this and have not looked after my drivetrain very weel. Only commute on the bike but I would think clean it all up about once every two or three months. I have an LX chainset with alloy rings so would be surprised if these didn't wear at the same rate? Also, what about jockey wheels?

The reason chain rings last longer than the cassette is because there are more teeth on a chain ring than what there are on a sprocket, thus the wear over time is less concentrated on the chain ring.

I have used an LX Chainset before and most of the time I had to just replace the middle ring, and only once the outer. If there's any more than one chainring needing replaced and you're using LX then it's better just to buy a whole new chainset.

I usually buy the new chain and cassette first, test it on the existing chainrings to see if the chain starts slipping, and then buy a new chain ring/chainset or leave the existing ones as they are.