Small Sprocket Wear Rates

[Mick F]

From my experience of 12t sprockets on Mercian, they've lasted about 7,000miles before a new chain would skip on them.

I fitted a new chain on Moulton yesterday, and just got back from a ride - rain, damp, fog - but that's besides the point.
The new chain skips on the 11t cog. It's ok cruising, but as soon as I put even a little bit of strain on it, off it skips.
Distance?
Only 1,765miles.

How people get on with 10t cogs, I don't know. I would suspect that the wear rates of smaller cogs is exponentially greater the fewer teeth they have.

I already have a spare cassette with an 11t cog, so I'll fit the cog for tomorrow's ride. Meanwhile, I see that I can buy individual 11t cogs for peanuts. I may buy three to make up the order. Looks like I'll be fitting a new 11t sprocket every six months!
http://www.bike-discount.de/en/buy/shim ... g_id-10431

Yes, yes, I know I could just leave well alone and wear out the whole cassette and chain.

I measured the "old" chain only last week and it was one sixteenth of an inch over 36" .......... so hardly worn at all. The new chain works fine on the 12t cog without even the hint of a skip, so as far as I'm concerned, the 11t cog is scrap.

[NATURAL ANKLING]

Hi,
I hate 11T, they are not clever.

Make sure you don't have any stiff links, turn pedals backwards slowly (stationary bike) and look for any sign.

[PH]

Does the wheel size make a difference? The 11T on the Moulton will go round a lot more times per mile than the 12T on the Mercian, though each time it's propelling you a lesser distance. I don't know how much one cancels the other out, but think there's a lot more at play here than the number of teeth.
Plus - I think you've said the Moulton is lower geared, could it be that you're spending more time in the bigger gears?

[Brucey]

All (small) sprockets that have integral spacers are manufactured using a different route vs the larger ones (which use separate spacers). This leads to the possibility that they will wear more quickly than larger sprockets, because they are perhaps softer.

Small sprockets also wear more quickly because each tooth does more work (per turn of the pedals), and the teeth cannot share the chain load so uniformly because the chain wrap encompasses fewer teeth. In addition each chain link articulates through a larger angle when it engages and disengages from small sprockets, increasing the scope for wear.

11T sprockets are also rather inefficient. I much prefer cassettes that don't have them, although if you have a small-wheeler that uses derailleur gears only, it is arguably the lesser of two evils if the other choice is an enormous (and expensive) big chainring to get the gears you want.

FWIW you can de-hook a worn small sprocket of this sort, but it won't stop it from skipping entirely, because the part of the tooth where a new chain's roller bears is also worn, such that the chain is trying to 'climb off the sprocket' under load.

cheers

[NATURAL ANKLING]

Hi,
After converting one of my skip trainers to 8S, I then realised that on 8S its just 7S + 11T

The whole idea of gearing of my skip trainers is to end up with a top gear which I can push on the flat with a 50Ib bike using 2" tyres

42X11 is to high for me which mean that my only gain is going from 14 useable gears to 15 (don't use granny for training), hardly worth the extra dish.

On the tourer I only have 42X11 too, OK so a lighter bike with slicker tyres might be worth higher gearing but how often anyone would use it on anything less than a 10 mile TT is debatable?

Maybe Mick F should of gone for 24" wheels instead

[Mick F]

Does the wheel size make a difference?

I'm sure it does.
Maybe one of our mathematicians on here could work out the difference.

Moulton has 20" wheels = 18.5" diameter, and Mercian 700c = 26.5" diameter. This means only 8" diameter difference ie 25" difference in circumference.

Circumference of Moulton is 58"
Circumference of Mercian in 83"

.................... my brain hurts!

Come on, someone workout out please.
How much further would my worn 11t cog have achieved had it been on Mercian instead of Moulton?
50% further?
Instead of 1,765miles, it could have gone on to a (massive) 2,700miles?
Still rubbish IMHO.

[NATURAL ANKLING]

Hi,
Do this-

Mount bike on stand and engage large chainwheel then a 13 t on cassette, wind it up hard and fast with hand and listen.

Now repeat with a 11T?

[JonMcD]

Does the set-up on the rear derailleur/chain length make a difference, or is it almost inevitable that the chain feeds onto the small sprocket around the 6 O’clock position? I have always tried to ensure that the 11t sprocket has as much chain as possible wrapped around it, although it may be that only a few teeth around the 12 O’clock position take the wear.

[Mick F]

Do this-
Mount bike on stand and engage large chainwheel then a 13 t on cassette, wind it up hard and fast with hand and listen.
Now repeat with a 11T?

Yes, 11t is noisy and notchy.
Obviously IMHO and a 10t would be terribly noisy.

Does the set-up on the rear derailleur/chain length make a difference?

I'm sure it does, but I've altered nothing, other than fit a new chain.
I like to have at least two chains on the go, and swap them now and again. One clean, and one in the wash, perhaps?

I took a photo (with my new phone) of the problem 11t.
It's very clear indeed when you look ................ Hooked teeth.
Click for a bigger view, and look at the gap between the ME and 11t.

[hamster]

The other issue is that Shimano have very short teeth to give very fast shifting. SRAM cassettes definitely last longer for me and I suspect the teeth are a bit longer, which means they are better able to take the load and wear over a larger area.

[Brucey]

re the wheel size effect; assuming that you would get a similar gear ratio with an 11T sprocket (which is almost certainly not the case) the small wheeled machine has the sprocket twirling round faster but also under a lower load, for any given power output to the rear wheel.

Thus it isn't obvious which is the greater effect; how many times the thing goes round vs the load seen.

A more realistic comparison might be using a sprocket that is pro-rata larger with wheel size, to give the same gear ratio. Taking this line if you use the same chainring size, the large wheeled bike will be running a ~16T sprocket for the same gear ratio as the smaller wheeled bike gets with an 11T sprocket. I think we all know that the 16T sprocket will last much longer than the 11T one!

cheers

[mercalia]

Do this-
Mount bike on stand and engage large chainwheel then a 13 t on cassette, wind it up hard and fast with hand and listen.
Now repeat with a 11T?

Yes, 11t is noisy and notchy.
Obviously IMHO and a 10t would be terribly noisy.

Does the set-up on the rear derailleur/chain length make a difference?

I'm sure it does, but I've altered nothing, other than fit a new chain.
I like to have at least two chains on the go, and swap them now and again. One clean, and one in the wash, perhaps?

I took a photo (with my new phone) of the problem 11t.
It's very clear indeed when you look ................ Hooked teeth.
Click for a bigger view, and look at the gap between the ME and 11t.11t Hooked Teeth.jpeg

They are like that new? I assume you not saying they arent?

[Mick F]

They are like that new? I assume you not saying they arent?

I've already fitted the new 11t, but in the interests of fairness, I take it off shortly, and photograph the pair side by side, or on top of each other ......... or something.
Back later with that.



My Moulton's top gear is 61/11 = 101.5 gear inches.
To have a 12t smallest, I would need a 66t chainwheel .......... sounds expensive.
Very cheap to buy a few 11t sprockets for a couple of quid each and change them every few months.

TBH, 101.5" isn't high enough for me. I'd like circa 115", so I would need 75/12 ................. very expensive.

BTW, I have 53/12 on Mercian, which gives 115.7"

[PH]

They are like that new? I assume you not saying they arent?

I've already fitted the new 11t, but in the interests of fairness, I take it off shortly, and photograph the pair side by side, or on top of each other ......... or something.
Back later with that.



My Moulton's top gear is 61/11 = 101.5 gear inches.
To have a 12t smallest, I would need a 66t chainwheel .......... sounds expensive.
Very cheap to buy a few 11t sprockets for a couple of quid each and change them every few months.

TBH, 101.5" isn't high enough for me. I'd like circa 115", so I would need 75/12 ................. very expensive.

BTW, I have 53/12 on Mercian, which gives 115.7"

So do you think you spend more time in the top gear?

[Mick F]

So do you think you spend more time in the top gear?

Yes.
Definitely.
Absolutely definitely.

Moulton't top gear is like Mercian's 14t which is three cogs in. Mercian has two more ratios higher than Moulton.
Bottom gears are similar. Moulton 22.2" and Mercian 24.5"

I took a photograph using my elderly digital camera set to macro.
It's a bit difficult to get the angle right to reduce parallax errors. I place the worn 11t directly on top of the new 11t and you can see the difference quite well I think. The new cog is peeping behind past the worn old cog.
Comparing the "old" 12t and the new 12t, they are identical, but the 11t cogs are visibly different. Far easier to see with the naked eye than to set up a photograph on a piece of paper on the kitchen table.

Click for a bigger view.