Where does the load & wear take place?

[simonineaston]

Thinking about the forces that apply to the chain and sprockets, does anyone know where most of the force / wear takes place? The chain, with its links, transfers power applied by the rider, through the cranks, rotating the front sprocket and that force is tranferred to the rear wheel by the chain, which hauls the rear wheel round by applying force to the teeth of the rear sprocket (or at least, that's how I understand it...). Presumably those forces are distributed across a number of teeth at any one time - the teeth at the bottom of the sprocket receive no pressure - the chain is not wrapped around the whole sprocket - whereas the teeth near the tangent of the chain are presumably bearing the brunt of the force. Does anyone know where this is explained, preferably in picture form!
Obviously, due to the fact that both sprockets go round and round, the wear is going to be evenly distributed across all teeth, but I was curious to learn about the forces, with a view to making sure my chain wraps around enough of the rear sprocket, when I position the chain tensioner, on my new build.

[Jdsk]

The Power Transmission chapter of Bicycling Science describes efficiency and the effect of small sprockets, and is very good on alternatives. But AFAICT doesn't have anything on the load and wear of teeth at various positions of engagement with the chain.

Jonathan

[hamster]

One other point to add is that the load is not even around the chainring - tension is lowest when cranks are vertical so chainring wear is least then.

[reohn2]

Front chainrings wear unevenly due to pedalling forces not being equal throughout their circumferance.
Rear sprockets wear evenly due to forces being applied evenly because they aren't always in the same relation to the chainrings.


Chain wear is even thoughout it's length,though side plate wear on a deraileur system is also a factor especially where cross chaining is prevalent,which in time leads to poor/slow gear changes even though the chain appears not to have worn linearly(stretched).

EDIT:- just to add,wear rate is accelerated greatly when a drivetrain is let to get dirty and or not lubed.

[simonineaston]

One other point to add is that the load is not even around the chainring - tension is lowest when cranks are vertical so chainring wear is least then.

I hadn't thought of that - but now you mention it, it makes sense. And that uneveness will be passed to the rear sprocket inevitably! However, over the lifetime of a cog, I guess it'll be averaged out.
I started to think about this when I offered up the chain tensioner on my new build, and intution told me to wrap as much of the chain round the rear sprocket as poss.. Then I thought, "I bet the chain only needs to be wrapped around some of the teeth and not most..." And then I realised that if you go far enough along that route, you could end up with a chain that's wrapped around a single tooth only, which is plainly silly... So where is the point at which it becomes needless to have more wrap?

[simonineaston]

side plate wear on a deraileur system is also a factor

Not in this case, as there's only one rear sprocket (on an Al-fee-nay).

[Jdsk]

One other point to add is that the load is not even around the chainring - tension is lowest when cranks are vertical so chainring wear is least then.

Front chainrings wear unevenly due to pedalling forces not being equal throughout their circumferance.

Can you see that pattern of wear in practice?

Thanks

Jonathan

[simonineaston]

I guess that idea was behind the design of the so-called biopace chainrings of the '80s...

[Jdsk]

Yes, but about better power delivery rather than lower wear.

Jonathan

[reohn2]

One other point to add is that the load is not even around the chainring - tension is lowest when cranks are vertical so chainring wear is least then.

Front chainrings wear unevenly due to pedalling forces not being equal throughout their circumferance.

Can you see that pattern of wear in practice?

Thanks

Jonathan

Yes and moreso on tandem timing rings that are smaller (39 or 42t) that are ridden to more extreme wear rates

[reohn2]

Yes, but about better power delivery rather than lower wear.

Jonathan

I had a 1055 Biopace Biopace chainset and couldn't tell the difference between them and round rings

[simonineaston]

The Power Transmission chapter of Bicycling Science describes efficiency and the effect of small sprockets, and is very good on alternatives. But AFAICT doesn't have anything on the load and wear of teeth at various positions of engagement with the chain.

Tell me more about this book, Jonathan - is it a right good rollicking read? Will I enjoy it? Should I spend the book token my auntie gave me last Xmas??

[Jdsk]

Bicycling Science, Wilson (and now Schmidt)
https://mitpress.mit.edu/books/bicycling-science-fourth-edition

It's excellent. But because of the wonder of the Web you can now find most of it elsewhere. I like having the book. I haven't looked at the fourth edition... yet.

Jonathan

PS: I won't give away the ending. : - )

[Brucey]

One other point to add is that the load is not even around the chainring - tension is lowest when cranks are vertical so chainring wear is least then.

this is (only) approximately true. You can see this looking at wear patterns in chainrings, and experimental data re pedalling action.

Even with new chain and sprockets, the load is borne by relatively few teeth on the sprocket at any one time. I think the worst (fastest) wear occurs when the chain rollers have to move much as the load is borne on each tooth, and that this usually occurs when the chain is worn vs the sprocket.

cheers

[Jdsk]

One other point to add is that the load is not even around the chainring - tension is lowest when cranks are vertical so chainring wear is least then.

Front chainrings wear unevenly due to pedalling forces not being equal throughout their circumferance.

Can you see that pattern of wear in practice?

Thanks

Jonathan

Yes and moreso on tandem timing rings that are smaller (39 or 42t) that are ridden to more extreme wear rates

Thanks

Jonathan