Help! Chain dropping issue on sons race bike

othello

I'm having a recurring problem with the chain dropping off the chainring on my sons race bike. His chain has come off in two races this season, including 3 times in one race on Saturday (the circuit was very bumpy with poor surfacing). Father son relations are not good

This is his current bike, which is running a single ring up front as he is gear restricted (he is 10).



After the first dropped chain I added the MTB XC chain guide pictured to try and keep it on. But his chain came off 3 times on Saturday even with that. It seemed to come off after the chain guide, at about 3 o'clock when looking at the chainset, and wrapped itself around the crank.



Here is the chain line from the back



My son hardly ever changes out of the smallest cog on the cassette for an entire race, and I wonder if chain line is the problem. Its currently set to work across the spread on the cassette.

I'm guessing I should:

* Take a couple of links out of the chain to increase the tension
* Move the single ring to the big ring position on the crank

Any other ideas? Do I need to play around with bb length to work on the chain line?

k-dog

The chain does look a little long.

If he stays in that gear you could change the chainring to the outer position - that would give a better chainline - but it would be worse for the bigger end of the cassette obviously.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19625834#p19625834]k-dog[/url] wrote:

The chain does look a little long.

If he stays in that gear you could change the chainring to the outer position - that would give a better chainline - but it would be worse for the bigger end of the cassette obviously.

Thanks. I'll drop a couple of links out and see.

On a 20min circuit race he will hardly ever change out of top gear, and at most might go 2 or 3 gears lower.

dj58

[quote
On a 20min circuit race he will hardly ever change out of top gear, and at most might go 2 or 3 gears lower.[/quote]

In that case you may as well move the chainring to the outside and see if it is any better.

imposter2.0

Not sure what gear combo you are running, but I would be inclined to go bigger on the front and correspondingly bigger on the back (so you end up with the same/similar roll-out). Might mean blocking off a couple of sprockets at the back, but looking at that chainline, it's probably no bad thing. The chain is more likely to hold onto bigger sprockets/rings anyway.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626164#p19626164]Imposter[/url] wrote:

Not sure what gear combo you are running, but I would be inclined to go bigger on the front and correspondingly bigger on the back (so you end up with the same/similar roll-out). Might mean blocking off a couple of sprockets at the back, but looking at that chainline, it's probably no bad thing. The chain is more likely to hold onto bigger sprockets/rings anyway.

To get within the U10 gear limit the bike is running a 35t with a 14x25 10spd cassette. This brings it just under with a little bit of leeway for different gear check lines at races. I originally had it set-up with a 36t front but that was so tight I dropped a tooth.

Problem is, I haven't been able to come up with a good alternative gear set-up to keep within the 5.4m rollout. Especially one that allows for a bigger front ring. Next year he moves up to U12 and there are more choices for meeting the 6.05m rollout.

imposter2.0

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626554#p19626554]othello[/url] wrote:

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626164#p19626164]Imposter[/url] wrote:

Not sure what gear combo you are running, but I would be inclined to go bigger on the front and correspondingly bigger on the back (so you end up with the same/similar roll-out). Might mean blocking off a couple of sprockets at the back, but looking at that chainline, it's probably no bad thing. The chain is more likely to hold onto bigger sprockets/rings anyway.

To get within the U10 gear limit the bike is running a 35t with a 14x25 10spd cassette. This brings it just under with a little bit of leeway for different gear check lines at races. I originally had it set-up with a 36t front but that was so tight I dropped a tooth.

Problem is, I haven't been able to come up with a good alternative gear set-up to keep within the 5.4m rollout. Especially one that allows for a bigger front ring. Next year he moves up to U12 and there are more choices for meeting the 6.05m rollout.

Don't get too hung-up on hitting the roll-out number. When my son was U10 he was on 42x17, which is a good alternative and although well under the 5.4m rollout (at 5.28m), it never proved a disadvantage as he had some very good top 5 and top 10 results in the nationals. We just used a 10sp 14up cassette with the last three sprockets locked out. Never dropped a chain once. Bigger sprocket/ring option is the way forward, I reckon.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626637#p19626637]Imposter[/url] wrote:

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626554#p19626554]othello[/url] wrote:

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626164#p19626164]Imposter[/url] wrote:

Not sure what gear combo you are running, but I would be inclined to go bigger on the front and correspondingly bigger on the back (so you end up with the same/similar roll-out). Might mean blocking off a couple of sprockets at the back, but looking at that chainline, it's probably no bad thing. The chain is more likely to hold onto bigger sprockets/rings anyway.

To get within the U10 gear limit the bike is running a 35t with a 14x25 10spd cassette. This brings it just under with a little bit of leeway for different gear check lines at races. I originally had it set-up with a 36t front but that was so tight I dropped a tooth.

Problem is, I haven't been able to come up with a good alternative gear set-up to keep within the 5.4m rollout. Especially one that allows for a bigger front ring. Next year he moves up to U12 and there are more choices for meeting the 6.05m rollout.

Don't get too hung-up on hitting the roll-out number. When my son was U10 he was on 42x17, which is a good alternative and although well under the 5.4m rollout (at 5.28m), it never proved a disadvantage as he had some very good top 5 and top 10 results in the nationals. We just used a 10sp 14up cassette with the last three sprockets locked out. Never dropped a chain once. Bigger sprocket/ring option is the way forward, I reckon.

Thanks, thats very useful.

I'm going to try the shortened chain and adjust the chainline, as he only has 1 national left this Saturday (possibly another if we go to Scarborough but I'm reluctant), and I don't really want to swap everything out now. For next season at U12 I'm going to look at the bigger front ring option as you suggest though.

imposter2.0

Good luck on Saturday (Milton Keynes?) As someone else suggested, I think if you are planning to keep those ratios on the day, I would consider switching the front ring onto the outer position on the crank spider.

Larger rings are the way forward, definitely. All I've done now he is U12 is unlock two of the sprockets on the rear, so he's now on 42x15.

Rightarmbad

Sounds like the chain is worn, possibly the cogs too looking at the engagement on the top of the chainring.
If that is a Shimano chain, it's on backwards.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626777#p19626777]Rightarmbad[/url] wrote:

Sounds like the chain is worn, possibly the cogs too looking at the engagement on the top of the chainring.
If that is a Shimano chain, it's on backwards.

Its a KMC chain, not a Shimano one. The chainring is only a couple of months old and won't be worn. The chain has been on a while though, but then again he is not riding 1000s of miles on it. I've got a chain checker on order to check it anyway.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626789#p19626789]othello[/url] wrote:

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19626777#p19626777]Rightarmbad[/url] wrote:

Sounds like the chain is worn, possibly the cogs too looking at the engagement on the top of the chainring.
If that is a Shimano chain, it's on backwards.

Its a KMC chain, not a Shimano one. The chainring is only a couple of months old and won't be worn. The chain has been on a while though, but then again he is not riding 1000s of miles on it. I've got a chain checker on order to check it anyway.

Chain checked with a chain checker and its fine (not even hitting the 75% indicator yet)

othello

I've managed to do some fettling today.

I've moved the chain ring to the outer ring position on the cranks. This has improved the chainline a lot.



I have also removed some links. I was advised to take out 2 links, however I'm never certain if 2 links is 2 whole sets of links or 2 parts? Here is what I removed, which I think is too much.



Here is the set-up with the shortened chain. It now won't shift into the big rear sprocket as the chain is too tight -- I definitely need to add a link back in!



I've also removed the MTB chain guide as I couldn't get it to line up right with the new chainring position. It either caught the crank arm or rubbed the rings. I have gone for a front mech out of the spares bin in my shed, though it needs lining up correctly. Hopefully that should help keep the chain on.

k-dog

Yeah, I would have started with removing one link (which is half of what you did - you obviously have to take them off in pairs). That looks a bit short and would cause a problem if he tried to change too many gears - even by accident.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19628660#p19628660]k-dog[/url] wrote:

Yeah, I would have started with removing one link (which is half of what you did - you obviously have to take them off in pairs). That looks a bit short and would cause a problem if he tried to change too many gears - even by accident.

Yes, I'm an idiot and should have gone with one link.

I've left the pin in the plate on the part I removed. I assume with a KMC chain I can rejoin it?

othello

Good news! The new set-up worked flawlessly at the race on Sunday, and my son bagged a 4th in the U10s which he was delighted about.

Shortening the chain and adjusting the chainline made the most difference I think. But the switch to a front mech as a chain guide added a bit of security.