Thoughts on the 11 tooth cog

[mike killay]

Here I am stuck in the house with sleet falling outside and I began pondering on the problem with the 11 tooth cog which so often skips.
Generally it is thought that it is because the cog is too small and the chain simply does not get sufficient wrap around the cog.
But, in my experience, the skip is only momentary, as though it tried to change down a gear and changed its mind, rather than a full blown skidding over the tops of the teeth.
Often, the 11 t cog shows little sign of wear.
My bike has 8 cogs and one chain wheel. When I first bought a 21 speed bike, the retailer told me that it was only really a 9 speed, in that the 3 chain wheels lined up with cogs 2,4 and 6 and the largest chain wheel should never be run on the largest cog because that would be pulling the chain sideways too much.
So, does my present set up with one chain wheel and 8 cogs present too much 'Cross chaining' for the 11 t cog?
When the weather clears, I propose to dismantle my cassette and rebuild it with 5 gears, the ones that I mainly use and fill up the outer 3 spaces with the left over gears which I will never use.
This should reduce the cross chain stress on the 11t cog.
A further thought is that the cog itself might flex under strain, sufficiently enough to allow the chain rivets to contact the lifting sectors on the side of the next cog and thus apparently skip.
So, a further experiment will be to grind off the lifting segments on the cog next to the 11t cog.
My reason for posting is to see if anyone else has tried these remedies?

 

[selrahc1992]

Here I am stuck in the house with sleet falling outside and I began pondering on the problem with the 11 tooth cog which so often skips.
Generally it is thought that it is because the cog is too small and the chain simply does not get sufficient wrap around the cog.
But, in my experience, the skip is only momentary, as though it tried to change down a gear and changed its mind, rather than a full blown skidding over the tops of the teeth.
Often, the 11 t cog shows little sign of wear.
My bike has 8 cogs and one chain wheel. When I first bought a 21 speed bike, the retailer told me that it was only really a 9 speed, in that the 3 chain wheels lined up with cogs 2,4 and 6 and the largest chain wheel should never be run on the largest cog because that would be pulling the chain sideways too much.
So, does my present set up with one chain wheel and 8 cogs present too much 'Cross chaining' for the 11 t cog?
When the weather clears, I propose to dismantle my cassette and rebuild it with 5 gears, the ones that I mainly use and fill up the outer 3 spaces with the left over gears which I will never use.
This should reduce the cross chain stress on the 11t cog.
A further thought is that the cog itself might flex under strain, sufficiently enough to allow the chain rivets to contact the lifting sectors on the side of the next cog and thus apparently skip.
So, a further experiment will be to grind off the lifting segments on the cog next to the 11t cog.
My reason for posting is to see if anyone else has tried these remedies?

ive a b'twin triban with a 3 chainwheel front 8 cog rear setup(i replaced teh casette which now has an 11 tooth smallest cog rear) - it isnt (for now) a pedelec, though - but, for what its worth, i dont think teh retailer is right - i often had the largest chainwheel/smallest cog rear engaged (and standing/bouncing merrilly with all my weight) without ever experiencing any skipping. it might help if you could say when exactly it skips?

 

[selrahc1992]

ive a b'twin triban with a 3 chainwheel front 8 cog rear setup(i replaced teh casette which now has an 11 tooth smallest cog rear) - it isnt (for now) a pedelec, though - but, for what its worth, i dont think teh retailer is right - i often had the largest chainwheel/smallest cog rear engaged (and standing/bouncing merrilly with all my weight) without ever experiencing any skipping. it might help if you could say when exactly it skips?

sorry, meant largest chainring/largest cog; smallest chainring smallest cog..

 

[KTM Bike Industries UK]

the 11t cog is standard on pretty much all road and mountain bikes, so if you have a problem with it skipping it'll be trying to shift up or down... which is a set up issue. Probably your lower limit adjustment not set correctly.

 

[mike killay]

the 11t cog is standard on pretty much all road and mountain bikes, so if you have a problem with it skipping it'll be trying to shift up or down... which is a set up issue. Probably your lower limit adjustment not set correctly.

Don't think so.
I have exhausted all possible adjustments with no success.
Also, if you fit a new cog, it will run for a few months before skipping, so wear comes into it, although it is difficult, even with a strong magnifying glass to see any. What I cannot check is if the teeth remain in original alignment or have ever so slightly bent because of the effect of cross chaining.
And can you clarify that when you say that 11t cogs are standard on road and mountain bikes, whether these are single front chain wheel or 3 ring types?

 

[mike killay]

ive a b'twin triban with a 3 chainwheel front 8 cog rear setup(i replaced teh casette which now has an 11 tooth smallest cog rear) - it isnt (for now) a pedelec, though - but, for what its worth, i dont think teh retailer is right - i often had the largest chainwheel/smallest cog rear engaged (and standing/bouncing merrilly with all my weight) without ever experiencing any skipping. it might help if you could say when exactly it skips?

It skips when it likes , not regularly and I have been unable to attribute it to any particular part of my ride. I even went around a roundabout about 50 times to see if it would skip in the same place, but it never did. I have changed the chain 3 times so it is not chain related.
When you say triban, is this a recumbent?

 

[KTM Bike Industries UK]

And can you clarify that when you say that 11t cogs are standard on road and mountain bikes, whether these are single front chain wheel or 3 ring types?

single, double, or triple... road and MTB... 9, 10 and 11sp. Pretty much all cassette options on bikes use an 11th cog as the smallest one.

if you have a problem and its trying to jump up the cassette its because you've got the limit screw too far in, or your chainline is out.

If a chain is running straight along a cog, its only going to want to jump off if the chain line or the dérailleur is trying to pull it up the block.

Stand behind the bike and put the chain onto the 11th cog and have a look at the chainline and mech settings. If you've having a problem with it jumping it won't be the cassette thats causing it... especially as you've said its happened with more than one cassette.

 

[flecc]

While the efficiency loss of extreme cross-chaining is negligible, good practice is to change both ends to some extent to avoid it, and that's often referred to as "knowing how to use a derailleur". Doing that I'm sure will minimise the risk of sprocket jumping Mike.

Shimano's sprocket tooth profiles and faces are designed to assist chain lift when the change mechanism pushes the chain against the side of the sprocket. It follows that extreme cross-chaining does the same as a change mechanism in pushing the chain against the sprocket side, so it's logical to assume that chain lift may result.
.

 

[mike killay]

Flecc,
I think that that is what is happening. There are 8 gears on the cassette and one chain ring.
If a chain is running straight along a cog, its only going to want to jump off if the chain line or the dérailleur is trying to pull it up the block.
This is precisely what is happening. The chain line is at the gap between 4th and 5th cogs

 

[flecc]

That's not common with one chainring, being most likely to happen with triples when the chain is crossed right over from the two extremes.

I very much doubt the 11 tooth cog could distort to bias the chainline. I've never tried your remedies but have used spacers on crank spiders to bias a chainline a little towards the small cog end. Is there any possibility of you shifting the chainwheel outwards a little to achieve the same? Just one sprocket thickness shift should be enough to eliminate the jumping if chainline is a problem.
.

 

[Deleted member 4366]

This is precisely what is happening. The chain line is at the gap between 4th and 5th cogs

The top gear will never be in line with the large chainwheel. It's only when the chain is extremely out of line that there's a problem. The chain goes round both jockey wheels before it gets to the top gear, so it doesn't know or care about where it's come from. The job of the top jockey wheel is to hold the chain in line with the gears, so it's that that you have to pay attention to. The plane of the top jockey wheel should be in the same direction as the line between the two wheels, but the derailleurs often become twisted after some time or abuse. Check yours. If it isn't straight, twist it back. I'm with Colin. Most jumping comes from incorrect adjustment. Some systems need very precise setting. I've seen one where a washer was missing, so that the chain couldn't sit fully on the top gear because it was touching the frame. I've seen another randomly jumping that was caused by a small stone caught beteen the gears.

 

[Croxden]

I'm glad I have hub gears.

 

[Deleted member 4366]

Hub gears jump too if you don't adjust them properly, only much more suddenly, so you end up smashing your nuts on the crossbar!

 

[selrahc1992]

I'm glad I have hub gears.

ah, the great hub gear derailleur debate, more contentious than sectarian conflict, one thing I would say, liking both, is that derailleurs can be cheaper to fix

 

[Deleted member 4366]

I tried the throttle debate, but that didn't work, so I tried this one. If this doesn't work, I'll have one more go with helmets. After that, its back to Keeping up with the Kardashians for excitement.

 

[flecc]

Hub versus Derailleurs? Just buy an SRAM DualDrive and have both!
.

 

[Croxden]

Hub versus Derailleurs? Just buy an SRAM DualDrive and have both!
.

I have one on my Birdy and may have chosen that over the Rohloff if it had been available. I doubt if I would have had 5000 miles without incident though.