rear der sprocket capacity

[Richard Goodman]

What does the 'total capacity' of a rear derailleur mean? For example, the DuraAce GS has a 'total
capacity' of 38 teeth apparently, but, being a road derailleur surely this doesn't mean that the
largest sprocket size it would work with is 38 teeth does it?

Rich

 

[Tony Raven]

"Richard Goodman" <[email protected]> wrote in message
news:[email protected]...
> What does the 'total capacity' of a rear derailleur mean? For example,
the
> DuraAce GS has a 'total capacity' of 38 teeth apparently, but, being a
road
> derailleur surely this doesn't mean that the largest sprocket size it
would
> work with is 38 teeth does it?
>

Its the difference in teeth it will handle. So for example and 11-32 cassette has a difference of 21
teeth which means nominally you should have no more than a 17 tooth difference between the largest
and smallest front chainrings to stay within the total capacity. Most will go further than their
nominal capacity and you can go even further if you studiously avoid large-large and small-small
gear combinations.

Tony

--
"If you tell the truth you don't have to remember anything." Mark Twain

 

[David Nutter]

Richard Goodman <[email protected]> said:
> What does the 'total capacity' of a rear derailleur mean? For example, the DuraAce GS has a 'total
> capacity' of 38 teeth apparently, but, being a road derailleur surely this doesn't mean that the
> largest sprocket size it would work with is 38 teeth does it?

This should help explain it a bit:

http://www.bikepro.com/products/rear_derailleurs/rear_derailleurover.html

The choice of terminology is very poor I think: one tends to assume that total capacity and max
capacity are synonymous.

Regards,

-david

 

[Richard Bates]

On Fri, 12 Sep 2003 15:21:52 GMT, "Richard Goodman" <[email protected]> in
<[email protected]> wrote:

>What does the 'total capacity' of a rear derailleur mean? For example, the DuraAce GS has a 'total
>capacity' of 38 teeth apparently, but, being a road derailleur surely this doesn't mean that the
>largest sprocket size it would work with is 38 teeth does it?

Total Capacity is the amount of chain that your derailleur can wrap up. A longer caged mechanism
will wrap more chain and will therefore have a higher total capacity. It is expressed in terms of
teeth: not links, and is calculated thus:

[teeth on largest front chainring] - [teeth on smallest front chainring] + [teeth on largest rear
sprocket] - [teeth on smallest rear sprocket]

Or more simply, it is the difference between the extreme big-big and small-small combinations.

Hope this helps.

Love and sprockets from the other Rich x

--
Two drums and a cymbal fall over a cliff. Boom boom, Tish. Email address is false. It begins
thus: richard@

 

[Tony W]

"Richard Bates" <[email protected]> wrote in message
news:[email protected]...
>
> Total Capacity is the amount of chain that your derailleur can wrap up. A longer caged mechanism
> will wrap more chain and will therefore have a higher total capacity. It is expressed in terms of
> teeth: not links, and is calculated thus:
snip

Allow me to interrupt with a supplementary question.

What is the difference between a long and/or short cage mechanism? When should one use a long
and/or short?

Is it all to do with the capacity?

T

Confused as usual :~(

 

[Richard Bates]

On Fri, 12 Sep 2003 17:32:10 +0100, "Tony W" <[email protected]> in
<[email protected]> wrote:

>What is the difference between a long and/or short cage mechanism? When should one use a long
>and/or short?
>
>Is it all to do with the capacity?

Yes. When you switch to a chainring/sprocket combination that has fewer teeth, the excess chain
which is not wrapped around the cog wheels need to be stored somewhere. It's a bit like the zigzag
queueing system used on fairground rides.

A long cage has a long distance between the two jockey wheels. A short cage has the two jockey
wheels closer together. The longer the cage, the more chain it can wrap up.

Generally, bikes with double chainsets will be fitted with a short cage rear mech since the
difference in teeth between the two front chainrings is smaller than the difference in teeth on a
triple, which will therefore use a long cage.

--
Trying to lose weight? Why not just eat four chocolate covered wafer biscuits each meal? You'll soon
notice the pounds dropping off with the Kitkatkins diet! Spamtrap: Stop sleeping to email me.

 

[Richard Bates]

On Fri, 12 Sep 2003 17:39:59 +0100, Richard Bates
<[email protected]> in
<[email protected]> wrote:

>>Is it all to do with the capacity?
>
>Yes. When you switch to a chainring/sprocket combination that has fewer teeth, the excess chain
>which is not wrapped around the cog wheels need to be stored somewhere. It's a bit like the zigzag
>queueing system used on fairground rides.

Oh and to actually answer your question, longer cages have a higher capacity.

--
Trying to lose weight? Why not just eat four chocolate covered wafer biscuits each meal? You'll soon
notice the pounds dropping off with the Kitkatkins diet! Spamtrap: Stop sleeping to email me.

 

[Tony W]

"Richard Bates" <[email protected]> wrote in message
news[email protected]...
>
> Yes. When you switch to a chainring/sprocket combination that has fewer teeth, the excess chain
> which is not wrapped around the cog wheels need to be stored somewhere. It's a bit like the zigzag
> queueing system used on fairground rides.
>
> A long cage has a long distance between the two jockey wheels. A short cage has the two jockey
> wheels closer together. The longer the cage, the more chain it can wrap up.
>
> Generally, bikes with double chainsets will be fitted with a short cage rear mech since the
> difference in teeth between the two front chainrings is smaller than the difference in teeth on a
> triple, which will therefore use a long cage.

Ting. Finally the penny drops. Thanks.

T

 

[Zog The Undenia]

Richard Goodman wrote:
> What does the 'total capacity' of a rear derailleur mean? For example, the DuraAce GS has a 'total
> capacity' of 38 teeth apparently, but, being a road derailleur surely this doesn't mean that the
> largest sprocket size it would work with is 38 teeth does it?

FWIW, I use a short 105 road mech on my MTB. Horrible things will happen if the gears are changed to
big-big by accident, but I've never done it. It tends to pick up fewer twigs and bits of grass
because it's an inch or two higher than an XT mech (and it's a little bit lighter).

 

[Richard Goodman]

"Tony Raven" <[email protected]> wrote in message
news:[email protected]...
> Its the difference in teeth it will handle. So for example and 11-32 cassette has a difference of
> 21 teeth which means nominally you should
have
> no more than a 17 tooth difference between the largest and smallest front chainrings to stay
> within the total capacity. Most will go further than their nominal capacity and you can go even
> further if you studiously avoid large-large and small-small gear combinations.
>

Thanks Tony and others. I sort of thought that it meant difference in numbers of teeth from
big-small, but hadn't thought to include the difference on the chainrings as well, so I just
couldn't figure it out. Now you mention it of course it makes sense....

Rich

 

[M Series]

Zog The Undeniable <[email protected]> wrote:
> Richard Goodman wrote:
>> What does the 'total capacity' of a rear derailleur mean? For example, the DuraAce GS has a
>> 'total capacity' of 38 teeth apparently, but, being a road derailleur surely this doesn't mean
>> that the largest sprocket size it would work with is 38 teeth does it?
>
> FWIW, I use a short 105 road mech on my MTB. Horrible things will happen if the gears are changed
> to big-big by accident, but I've never done it. It tends to pick up fewer twigs and bits of grass
> because it's an inch or two higher than an XT mech (and it's a little bit lighter).

I used to use a 105 short cage on my #2 road bike with 30/39/53 up front and 13-24 on the rear. I
don't even consider using the smallest front and 2 smallest rear/ largest front and 2 largest
rear. It worked fine. One does not HAVE to replace the rear mech when upgrading the front chainset
to a triple.

 

[Pete Biggs]

M Series wrote:
> I used to use a 105 short cage on my #2 road bike with 30/39/53 up front and 13-24 on the rear. I
> don't even consider using the smallest front and 2 smallest rear/ largest front and 2 largest
> rear. It worked fine.

It still makes sense to have the chain long enough for the largest chainring + largest sprocket
combination in case it is accidentally selected one day.

> One does not HAVE to replace the rear mech when upgrading the front chainset to a triple.

I wouldn't use a short cage with a triple but apparently some people do manage to.

~PB