Derailleur capacities?
DaveC
front: 22/32/44
rear: 11/34
f & r derailleurs: m900 (early Shimano XTR)
Rear derailleur says "max 32T, total 33T". Why 2 numbers?
I need a r. derailleur with capacity of 45. Can I simply replace the cage on
this derailleur with a longer one?
The front derailleur is 26T capable (I found this number on-line). Is this
compatible with my chain rings?
Thanks.
landotter
> Building a 27s mtb using these parts:
>
> front: 22/32/44
> rear: 11/34
> f & r derailleurs: m900 (early Shimano XTR)
>
> Rear derailleur says "max 32T, total 33T". Why 2 numbers?
>
> I need a r. derailleur with capacity of 45. Can I simply replace the cage on
> this derailleur with a longer one?
You'll definitely want a long cage for such a wide set of gearing.
However, don't know what's stock on your current one. It's easy enough
to adjust your chain length to be the absolute shortest it needs to be
to handle large large. Then shift into small-small and see if the cage
takes up enough chain sag. You might be compelled to live with a
little sag--as that's not a commonly used gear anyway.
>
> The front derailleur is 26T capable (I found this number on-line). Is this
> compatible with my chain rings?
>
No problem.
Tom Ace
> Rear derailleur says "max 32T, total 33T". Why 2 numbers?
The max 32T is the largest rear sprocket it'll be happy with.
The total 33T is the largest difference in front+rear teeth
(big+big)-(small+small) that it'll be able to take up slack for.
Tom Ace
DaveC
> The max 32T is the largest rear sprocket it'll be happy with.
> The total 33T is the largest difference in front+rear teeth
> (big+big)-(small+small) that it'll be able to take up slack for.
>
> Tom Ace
Thanks, Tom.
So my cassette, having a low of 34, is too large for this derailleur? It
won't go onto that gear?
And having (per formula) need for total of 45, it looks like I'll have
significant slack, yes?
Is it possible (and probable?) to find a longer cage for this model (M900)?
Are cages from other Shimano models interchangeable?
Thanks.
Frank Krygowski
> >> Rear derailleur says "max 32T, total 33T". Why 2 numbers?
> > The max 32T is the largest rear sprocket it'll be happy with.
> > The total 33T is the largest difference in front+rear teeth
> > (big+big)-(small+small) that it'll be able to take up slack for.
>
> > Tom Ace
>
> Thanks, Tom.
>
> So my cassette, having a low of 34, is too large for this derailleur? It
> won't go onto that gear?
>
> And having (per formula) need for total of 45, it looks like I'll have
> significant slack, yes?
Manufacturers tend to be pretty conservative about these numbers.
It's often possible to exceed that stated "max cog" capacity by a
couple teeth. And regarding the chain wrap capacity - if you never
ride in the small-small combination (which you shouldn't any way) you
probably don't need the chain wrap to cover it. If you do shift into
a couple of too-small cogs, your chain will just hang loose on the
bottom. It's usually not a problem, at least in my experience.
- Frank Krygowski
Hank
RD-M900 was mid-cage (GS) only. First XTR long-cage (SGS) was RD-M910,
released 4 years later.
Shimano parts are typically riveted or swaged together, and small
service parts aren't available. Anybody can feel free to correct me,
but I don't think it's swappable
Capacity numbers are famously conservative. Crank down the b-tension
screw at the mounting pivot, and you'll probably get on that 34t fine,
but as a "racing" group, it was intended for close-ratio cassettes,
with a triple in front.
RonSonic
Hey Dave, nothing personal here, just Ron being Ron ...
Where do you live and how wildly aggressively do you ride to need that range?
That 44x11 should get you to 35mph without spinning wildly and the 22x34 will do
a brisk walk while spinning furiously. It'll do it straight up a cliff if you
could get traction. If you live on a mountain, okay maybe.
XTR is basically a XC racing group. It's nice and it's light but not intended to
pull that much chain. Most guys racing will seriously narrow down their gearing
to not have large gaps or include cogs that they won't use.
The cages are generally not interchangeable in Shimano stuff. They don't
usually come off.
--
Oh damn. There's that annoying blog. Again. http://dumbbikeblog.blogspot.com
AMuzi
Capacity is a bit conservative; I would set it up and, if it
is not suitable, just replace it. Forget modifying a modern
Shimano rear changer.
Especially set chain length to big-big plus two rivets.
Don't skimp on that.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971