Chain Line Angle

[gbbird]

Just finished building my first ever MB from scratch, and took it out for it's maiden ride All is working smoothly and perfectly, EXCEPT when i am on the outer front chain ring and the inner (largest) two rear chainrings at the rear cog, the angle of the chain is such that the chain drags sideways off the biggest two rear cogs. The chain does not come off, just makes a noise at it scrapes sideways on the rear teeth. All other gears work fine.

I run a Shimano Deore front chainset and crank with Deore BB, and a Shimano LX rear cog. Now, i guess that to adjust the chainline and solve my problem, i either have to move the front chainwheel closer to the frame or the rear cog outwards slightly. We are talking one or two mm at the most. Can this be done, and if so how?

Many thanks

Greg

[neil_bolton]

gbbird said:

Just finished building my first ever MB from scratch, and took it out for it's maiden ride All is working smoothly and perfectly, EXCEPT when i am on the outer front chain ring and the inner (largest) two rear chainrings at the rear cog, the angle of the chain is such that the chain drags sideways off the biggest two rear cogs. The chain does not come off, just makes a noise at it scrapes sideways on the rear teeth. All other gears work fine.

I run a Shimano Deore front chainset and crank with Deore BB, and a Shimano LX rear cog. Now, i guess that to adjust the chainline and solve my problem, i either have to move the front chainwheel closer to the frame or the rear cog outwards slightly. We are talking one or two mm at the most. Can this be done, and if so how?

Many thanks

Greg

You'd just purchase a slightly less wide BB (axle) for your frame. This meaas the chainset is too far outboard of the frame (only takes a few millimetres.)

The most common BB axle width is about 113 - You may, by the sounds of it, be running 118.
Check the packaging it came with, if not that, measure from edge to edge of the axle, in mm.

This gives you your axle width, and you can decide what size to buy from there.

What frame is it?

Edited by neil_bolton on Wednesday 4th July 13:53

[snotrag]

Come on Neil, I've come to expect better!

Short answer - don't do it.

You shouldnt be using this combination of chainring/sprockets - the gear ratio is the same as what you'll find by using the middle chainring and middling sprocket.

Crossing the chain line does nothing except promote wear and lead to premature stretching of the chain. Its something I was continually explaining to customers when selling bikes, some jsut could not get it.

In short, yes, it will probably rub, beacuse your using it wrong.

Of course, this advice also goes for using the inner chainring and the out sprockets aswell.

Too many people have this annoying habit of never using the front derrailleur, and then complaining about poor shifting up and down the block and rubbing/noise.

Use the full range of gears properly, and you'll have no problem. HTH!

[snotrag]

Edit to say - not disagreeing with you Neil - this problem would be exacrebated by having a BB too long - but still, shouldnt be doing it.

[neil_bolton]

snotrag said:

Edit to say - not disagreeing with you Neil - this problem would be exacrebated by having a BB too long - but still, shouldnt be doing it.

np at all dear Snotters

I must admit my first thought was the same - why one earth are we worrying about a chainline on the extremes.

However, it must be said, you can reliably and quietly run extreme chainlines only if you have the BB lenght absolutely bang on.

Having said that, (even though I do it all the time myself being a big ring monster) you shouldn't be running extreme lines.

If it really bothers you check out the BB length else put up with it.

Edited by neil_bolton on Wednesday 4th July 14:56

[snotrag]

You can also drive a Land Rover down the M1 in '4wd-low', but you probably shouldn't

Its not something that bothers me anyway - I regularly go XC riding on my 40lb single chairning bike, and my 'light' (guffaw) bike has a two + bashguard.

[gbbird]

Thanks all. Neil - the BB is 113mm, the frame is a Cove Stiffee

regards

g

[neil_bolton]

snotrag said:

You can also drive a Land Rover down the M1 in '4wd-low', but you probably shouldn't

Its not something that bothers me anyway - I regularly go XC riding on my 40lb single chairning bike, and my 'light' (guffaw) bike has a two + bashguard.

Ahh, but the XTR I have is super tough and slick so its ok