Chain guide or not?

othello

We had our first proper muddy CX race on Sunday (National Trophy) and my son managed to drop his chain numerous times. He is running 1x11, with a single SRAM N-Sync chainring up front. I had removed the chain guide from his Giant TCX, as the NW ring should hold the chain on enough. Also if the chain does come off, its much harder to get it back on with a guide!

Should I put the chain guide back on?

The chain dropping issue was effecting lots of riders, though I would like to try and work out why it was effecting him. Maybe the gears were slightly out (not enough to clatter), which was enough. he has only had the bike since September so there is no wear on the ring/chain.

trek_dan

Clutch in mech working? Chain length too long?

othello

trek_dan wrote:

Clutch in mech working? Chain length too long?

Clutch working and chain the stock length (which looks to be fine as the mech is pulled quite far forward when in the lowest gear).

Haven't had a problem in bumpy races so far this season. Just as the mud got sticky...

tgotb

Was it happening with a clean bike, or only after a couple of laps? How much debris was there in the rear mech by the time he finished? Any particular part of the course? Did you clean the mech thoroughly between his sighting laps and the start?

One thing that can happen, even with a clutch mech, is that the mech clogs sufficiently that it won''t let the chain run cleanly when you back pedal. This allows the top run of chain to go slack, and it can then drop when you start pedalling. You don't have to backpedal far, a fraction of a revolution is enough.

I was pitting for a couple of riders in the senior women's race who were both changing every lap; their mechs were collecting serious quantities of debris. My daughter raced in the juniors, didn't want to change bikes, and collected enough debris in just over 2 laps to jam her mech solid and send it into the wheel.

othello

TGOTB wrote:

Was it happening with a clean bike, or only after a couple of laps? How much debris was there in the rear mech by the time he finished? Any particular part of the course? Did you clean the mech thoroughly between his sighting laps and the start?

One thing that can happen, even with a clutch mech, is that the mech clogs sufficiently that it won''t let the chain run cleanly when you back pedal. This allows the top run of chain to go slack, and it can then drop when you start pedalling. You don't have to backpedal far, a fraction of a revolution is enough.

I was pitting for a couple of riders in the senior women's race who were both changing every lap; their mechs were collecting serious quantities of debris. My daughter raced in the juniors, didn't want to change bikes, and collected enough debris in just over 2 laps to jam her mech solid and send it into the wheel.

It was happening on both bikes (identical Giant TCX's), and during the race at various points the lap. He did his sighting laps on his 2nd bike, and started the race on the clean race one. But it happened throughout the race, though oddly not on the last lap. We were changing each lap, and he had it drop on both bikes.

I did ask him if it happened at particular points on the course, to see if there was a pattern. But he wasn't sure it was the same place.

He did have it come off after the steep uphill bank before the steps. He went into the deep rut, and I wonder if the rut was so deep, the rear mech dragged into the mud and got clogged.

It's a good point about that chain going slack at the top though. One place he dropped was just after the steps as he came to remount, and if he flicked the pedals back slightly when going up the stairs, that would be why.

From what you've said, it does make me think a chain guide is the way forward to stop that from happening. It would keep the top run of chain more in place. Do you think?

tgotb

othello wrote:

From what you've said, it does make me think a chain guide is the way forward to stop that from happening. It would keep the top run of chain more in place. Do you think?

Sounds like it could be worth a try. I've always avoided using chain guides, partly because of a concern about them collecting mud, and partly because of the problems they cause if the chain does come off. Sounds like you're conscious of those factors though.

Was he faster during the last lap, when the chain stayed on? If so, that might support the theory of freewheeling (and possibly minor back-pedalling) being part of the process that causes it to drop.

othello

TGOTB wrote:

Sounds like it could be worth a try. I've always avoided using chain guides, partly because of a concern about them collecting mud, and partly because of the problems they cause if the chain does come off. Sounds like you're conscious of those factors though.

Yes, they are my concerns as well. Without the guide he was able to put the chain back on himself each time, though *very* slowly! I do worry if he had a guide it would be much bigger job, and he would have had to run.

TGOTB wrote:

Was he faster during the last lap, when the chain stayed on? If so, that might support the theory of freewheeling (and possibly minor back-pedalling) being part of the process that causes it to drop.

On the last lap he was really fast, and his lap times were the same as the top 10 or so riders.

I've put the guide on and we will see how it goes over the next week or so. We possibly have a muddy one at the weekend, so a chance to give it a try.