Rohloff Speedhub

I just put together a new bike using a Rohloff Speedhub 14-speed internally
geared rear hub. One basic question comes to mind now that I've ridden the
bike a few times. Why does a bike with a Rohloff Speedhub need such a
formidable torque arm while a convential rear hub/derailleur equipped bike
does not?

Per Chachi:
Why does a bike with a Rohloff Speedhub need such a
formidable torque arm while a convential rear hub/derailleur equipped bike
does not?

It doesn't.

The thing they ship is, to me, very un-GermanLike - especially the hose clamp
part... Gotta wonder if lawyers are involved.

Does your bike have disk brake mounts?

If so, spend a few bucks and get what Rohloff calls a "SpeedBone": basically an
adapter that lets you use the disc brake mounts even while disc brakes are
mounted. Much, much cleaner than the supplied torque arm. Sano, even....

If the bike has mounts but not disc brakes, it looks like the right kind of bolt
thru one of the mount holes *might* do the job... but disc brake or no disc
brake, I would spend the bucks on a SpeedBone before I bet life and limb on a
single bolt solution.
--
PeteCresswell

Chachi wrote:

Why does a bike with a Rohloff Speedhub need such a
formidable torque arm while a convential rear hub/derailleur equipped bike
does not?

To step torque up (or down), some part (sun, or planet carrier,
or annulus) of a planetary gear stage needs to be kept from
rotating; a QR or axle nut isn't enough for that purpose,
hence the torque arm.

By analogy: a lever can't increase (or decrease) mechanical
advantage without a stationary fulcrum.

A conventional hub doesn't step torque up or down. The only
torque that would tend to make the axle rotate is bearing drag,
small enough in magnitude to be resisted by a QR or axle nuts.

Tom Ace

Chachi wrote:

I just put together a new bike using a Rohloff Speedhub 14-speed internally
geared rear hub. One basic question comes to mind now that I've ridden the
bike a few times. Why does a bike with a Rohloff Speedhub need such a
formidable torque arm while a convential rear hub/derailleur equipped bike
does not?


Our Nexus 8 speed hub has a similar arm, but that also has a roller brake!

The Rohloff one is overbuilt - look at a Thorn with the purpose-made
Rohloff dropouts and you can see that such a long arm on other bikes is
unnecessary.

Chachi Wrote:
I just put together a new bike using a Rohloff Speedhub 14-speed
internally
geared rear hub. One basic question comes to mind now that I've ridden
the
bike a few times. Why does a bike with a Rohloff Speedhub need such a
formidable torque arm while a convential rear hub/derailleur equipped
bike
does not?

Conventional hub merely rotates on the axle. Splines transfer the
torque from the cogs to the hub bypassing the axle. The only torsional
load is from friction.

Gear hub generally needs to use the axle as a torsional anchor upon
which the gears turn.


--
meb

On 4 Nov 2005 21:52:35 -0800, "Tom Ace" wrote:

To step torque up (or down), some part (sun, or planet carrier,
or annulus) of a planetary gear stage needs to be kept from
rotating; a QR or axle nut isn't enough for that purpose,
hence the torque arm.

So why can all the other gearhubs make do with a simple keyed washer to
prevent the axle from rotating?

Jasper

I can understand that answer, thank you. I'm also hoping that someone with
specific knowledge about the Speedhub will answer the following...

The bike I just built up is a Surly Karate Monkey with horizontal dropouts
and International Standard disk brake mounts. I think the currently
installed torque arm is fugly.

Is it wise to use the Rohloff OEM2 axle plate in lieu of the torque arm on
this frame? I'm not so much concerned about the disk brake mount since the
bike is built like a tank and meets the Rohloff stated requirements. I'm
more concerned about the horizontal dropouts.

Are the direction and magnitudes of the forces so significant that the
torque might move the axle in the dropout?

Which direction might the axle move, forward or back?

The hub I have is a "TS" or Touring Special with solid axle and nuts (no
quick release).

"Tom Ace" wrote in message
oups.com...
Chachi wrote:

Why does a bike with a Rohloff Speedhub need such a
formidable torque arm while a convential rear hub/derailleur equipped
bike
does not?

To step torque up (or down), some part (sun, or planet carrier,
or annulus) of a planetary gear stage needs to be kept from
rotating; a QR or axle nut isn't enough for that purpose,
hence the torque arm.

By analogy: a lever can't increase (or decrease) mechanical
advantage without a stationary fulcrum.

A conventional hub doesn't step torque up or down. The only
torque that would tend to make the axle rotate is bearing drag,
small enough in magnitude to be resisted by a QR or axle nuts.

Tom Ace

Jasper Janssen wrote:

So why can all the other gearhubs make do with a simple
keyed washer to prevent the axle from rotating?

With its wide range, the Speedhub needs more torque
support than other internal gear hubs do.

In first gear, the Speedhub drives the rear wheel with 3.6 times
the input torque at the sprocket. Thus the torque arm supplies
a torque of 3.6 - 1, or 2.6 times the input torque.

Compare that to a Shimano Nexus 8, whose first gear drives
the wheel with 1.9 times the input torque. The axle needs to
be held with a torque of 1.9 - 1 = 0.9 times the input torque.

Even so, the length of the Rohloff arm may well be overkill.

Tom Ace

On Sat, 5 Nov 2005 10:58:33 -0500, "Chachi" wrote:

Are the direction and magnitudes of the forces so significant that the
torque might move the axle in the dropout?

Which direction might the axle move, forward or back?

Neither. Torque (wants to) move the axle around, not forward or back. It's
chain tension that wants to move it forward, but that shouldn't be a real
problem as long as you tighten the nuts sufficiently.


Jasper

Jasper Janssen Wrote:
On 4 Nov 2005 21:52:35 -0800, "Tom Ace" wrote:

To step torque up (or down), some part (sun, or planet carrier,
or annulus) of a planetary gear stage needs to be kept from
rotating; a QR or axle nut isn't enough for that purpose,
hence the torque arm.

So why can all the other gearhubs make do with a simple keyed washer
to
prevent the axle from rotating?

Jasper


In the case of my Sachs 7 speed, that keyed washer prooved to be
seriously inadequate.
Dan


--
Dan Burkhart