Hub gears

"Tom" <[email hidden]> wrote in message
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"Tumbleweed" <[email hidden]> wrote in message
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Can you explain why? As a layman in these matters it seems that unless

there

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is slippage you'd have close to 100% efficiency. Not disputing it would

just

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like to understand where the lost energy is going.

Friction (and therefore heat)

Tom

Sure but how? What is slipping to cause the friction?

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Tumbleweed

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Tumbleweed said:

"Tom" <[email hidden]> wrote in message
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Quoted message said:

"Tumbleweed" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Can you explain why? As a layman in these matters it seems that unless

there

Quoted message said:

is slippage you'd have close to 100% efficiency. Not disputing it would

just

Quoted message said:

like to understand where the lost energy is going.

Friction (and therefore heat)

Sure but how? What is slipping to cause the friction?

The chain-links pivoting, presumably.

--
Keith Willoughby http://flat222.org/keith/
I drove my tractor through your haystack last night

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If only I could find my college books on chain efficiency!

Graham.

IIRC a Renolds chain is 85% efficient.

"Tumbleweed" <[email hidden]> wrote in message
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Sure but how? What is slipping to cause the friction?

The gears are constantly meshing and un-meshing inside a hub gear, plus the
viscosity of the oil being moved around inside the hub are all sources of
friction. Not that I'm knocking hub gears, two of my bikes have SA hubs.

Tom

Tumbleweed said:

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A point about efficiency of chain drives, which is governed by the size
of the smallest sprocket of the pair. A 19T rear sprocket gives, as
best I recall, about 93% efficiency, in well lubricated conditions.
Smaller sprockets give lower efficiency, which will be further reduced
if out of alignment, as the higher 'gears' of a derailler are.

Can you explain why? As a layman in these matters it seems that unless there
is slippage you'd have close to 100% efficiency. Not disputing it would just
like to understand where the lost energy is going.

It's heating up the chain and making a noise.

Daniele

To Clive, the same! Hi there...

To Tumbleweed: there are various sources of small losses in a chain, as
there is slippage between the rollers and the pins they rotate on, also
between the pins connecting each link, in wrapping the chain around
each sprocket. This increases with smaller sprockets.

Hence a large sprocket causes less wrapping, or flexing, of the chain,
whereas a small sprocket causes a lot. After a thrash you will find the
chain is quite warm, on a motorbike it will be very hot, so take care
as you can burn your fingers!

When I fitted a new block to our tandem I chose one with a 14T high
gear, rather than its smaller predecessor, and restored overall gearing
at the front. I despair at 11T top gears, as they are very inefficient.

Hope that helps.

Graham.

Dave,

Many thanks for this link. The article actually goes into the theory of
chain efficiency in much greater detail than I ever did! The writers
also cover actual measurements taken in laboratory conditions,
employing a derailler mechanism in the drive train and using different
size sprockets (notably 11T, 15T and 21T) in conjunction with a 52T
chainwheel and they measured efficiency in many configurations.

The best figures recorded are 95%, 97%, 98% for 11, 15, 21
respectively. The poorest figures for the same sprockets were 84, 86,
88, but I recommend following the link and reading more (skip over the
maths!) to discover why there is this variation - it is not as simple a
subject as I suspect we would all like it to be. Seek out Issue 50,
2000 also 51, 2001.

Graham.

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To Clive, the same! Hi there...

To Tumbleweed: there are various sources of small losses in a chain, as
there is slippage between the rollers and the pins they rotate on, also
between the pins connecting each link, in wrapping the chain around
each sprocket. This increases with smaller sprockets.

Hence a large sprocket causes less wrapping, or flexing, of the chain,
whereas a small sprocket causes a lot. After a thrash you will find the
chain is quite warm, on a motorbike it will be very hot, so take care
as you can burn your fingers!

When I fitted a new block to our tandem I chose one with a 14T high
gear, rather than its smaller predecessor, and restored overall gearing
at the front. I despair at 11T top gears, as they are very inefficient.

Hope that helps.

Graham.

it does, thanks.

--
Tumbleweed

email replies not necessary but to contact use;
tumbleweednews at hotmail dot com