Sprocket query

[old trials fanatic]

I've got a question about sprockets. Now i've always believed that ideally you should have an odd number and an even number i.e. 11 tooth gearbox and 42 back wheel to ensure wear was more even on both sprockets. However the std combination is 11 gearbox 41 rear wheel. Wouldn't this wear the sprocket unevenly. Alternatively have i had it wrong all these years or doesn't it matter any more ?

[peterb]

I have never heard of any wear being related to the odd/even combination, only that with a 9T the sprocket and chain wear a bit quicker than with a 10T due to the smaller diameter, interesting though. Besides, sprockets and chains on trials bikes tend to last 1-2 years before needing renewal so probably not really worth considering in this case. Bye, Peter B.

[cleanorbust]

2 hours ago, old trials fanatic said:

I've got a question about sprockets. Now i've always believed that ideally you should have an odd number and an even number i.e. 11 tooth gearbox and 42 back wheel to ensure wear was more even on both sprockets. However the std combination is 11 gearbox 41 rear wheel. Wouldn't this wear the sprocket unevenly. Alternatively have i had it wrong all these years or doesn't it matter any more ?

I suspect I've been around trials about as long as you have but I've never heard the theory about odd/even sprocket wearing less quickly. I can"t figure out why that would be the case.

Any ideas on the theory behind this belief?

[greychapel]

Isn't that gears?

[lineaway]

 I think it was more confused with chain length. I remember having a World round bike, `92 Zero that had a 43 tooth sprocket that needed a half link to work. The half link on the production bikes are fairly common now, but their was a time that it was considered  poor engineering.

[feetupfun]

Maybe it is a variation of the recommendation to avoid having the small number divide evenly into the big number, like 10:40 or 11:44. Probably not relevant to trials bikes which kill chains with grit but apparently is important for road bikes that can do massive hours on a set of chain and sprockets.

The logic is that it is better to reduce the frequency of repeated patterns of tooth combination. For example with the 10:40, the same tooth on the rear sprocket is in contact with the one tooth on the front sprocket every time the wheel rotates.

[b40rt]

1 hour ago, feetupfun said:

 

 

 

 

1 hour ago, feetupfun said:

The logic is that it is better to reduce the frequency of repeated patterns of tooth combination. For example with the 10:40, the same tooth on the rear sprocket is in contact with the one tooth on the front sprocket every time the wheel rotates.

Every forth time ?

[feetupfun]

2 hours ago, b40rt said:

 

 

 

Every forth time ?

Yes the front sprocket takes four turns between the contacts. I said "every time the wheel rotates" which is the same thing.

[old trials fanatic]

21 hours ago, cleanorbust said:

I suspect I've been around trials about as long as you have but I've never heard the theory about odd/even sprocket wearing less quickly. I can"t figure out why that would be the case.

Any ideas on the theory behind this belief?

The theory goes that with both even number sprockets then the outer links and inner links always run on the same teeth wearing the sites of the sprockets accordingly. With an odd and an even number combination this doesnt happen resulting in more even wear to the sides of the sprockets. As previously mentioned though because in trials applications the chain and sprockets wear out so quickly it may be irrelevant. Perhaps more important on road bikes. Just asking.

[Moomoo]

22 hours ago, greychapel said:

Isn't that gears?

That's my understanding.

[eagle8]

My understanding is you don't want numbers that divide to an even number like 12/48 =4, you would be better off with 12/49 =4.083. If the number is even the same place in the chain will contact with the same place on the sprocket every few revolutions, if it is odd the chain will not hit the same place on the sprocket, so less wear ?

Edited January 26, 2020 by eagle8

[feetupfun]

3 hours ago, eagle8 said:

My understanding is you don't want numbers that divide to an even number like 12/48 =4, you would be better off with 12/49 =4.083. If the number is even the same place in the chain will contact with the same place on the sprocket every few revolutions, if it is not even the chain will not hit the same place on the sprocket, so less wear ?

Yes the chain length effect is real, but is a separate effect to the sprocket teeth ratio effect

[2stroke4stroke]

On 1/24/2020 at 10:28 PM, greychapel said:

Isn't that gears?

Yes, the hunting tooth. But trials chains don't run in an oilbath so any effect would be unmeasurable.

[b40rt]

21 hours ago, eagle8 said:

My understanding is you don't want numbers that divide to an even number like 12/48 =4, you would be better off with 12/49 =4.083. If the number is even the same place in the chain will contact with the same place on the sprocket every few revolutions, if it is odd the chain will not hit the same place on the sprocket, so less wear ?

What if you have a half link in the chain ? That would bugger the theory ?

[jon v8]

2 hours ago, 2stroke4stroke said:

Yes, the hunting tooth. But trials chains don't run in an oilbath so any effect would be unmeasurable.

Funny you should mention the hunting tooth - Reminds me of the bevel drive in the MHR Ducati I had. In that situation it was worthwhile. I last thought about it when I saw the wear on my WW2 Matchless cam gears,it was very obvious which teeth did all the work. But on a final drive chain,exposed to even road crud,I can't see any point in worrying.