Roller brake high speed performance.

Paul Murphy twisted the electrons to say:

Quoted message said:

I'm going to be more careful next time with front brake application but I'm
curious if this is common with hub brakes. Is there anything I can do to
prevent a recurrence next time I go down this hill (other than not going so
fast)?

I believe if you dump too much energy (ie: brake from too high a speed)
into the Nexus roller brakes then you boil the grease? The brake then
becomes *much* more effective, and this would correlate with you (almost)
emulating Superman.

As for preventing this, well going faster does mean you'll lose more
energy to aerodynamic drag. Perhaps regular reasonably sharp braking as
you come down the hill? Scrubs off quite a bit of speed, but then lets
your brakes cool down for the next time?
--
These opinions might not even be mine ...
Let alone connected with my employer ...

Paul Murphy said:

Going down a steep hill I recently got up to just over 40 mph. I
applied both roller brakes, which weren't very effective initially
but then suddenly the front brake grabbed, almost locking the wheel
(had I not released the brake lever straight away I would have
taken a flying lesson). The front and rear brakes are both Shimano
Nexus units and the bike is only 10 months old.

The service instructions say:

"When using the Shimano Inter-M brake system, avoid continuous
application of the brakes when riding down long slopes, as this will
cause the internal brake parts to become very hot, and this may weaken
braking performance. It may also cause a reduction in the amount of
brake grease inside the brake, and this can lead to problems such as
abnormally sudden braking."

and also:

"If braking force is abnormally strong ... the cause might be not enough
brake grease, so ask the place of purchase to grease the mechanism
with special roller brake grease."

Wiggle sells the grease - 6.99 for a decent size tube. Search for
'brake grease'.

regards, Ian SMith
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Paul Murphy said:

Going down a steep hill I recently got up to just over 40 mph. I
applied both roller brakes, which weren't very effective initially
but then suddenly the front brake grabbed, almost locking the wheel
(had I not released the brake lever straight away I would have taken
a flying lesson). The front and rear brakes are both Shimano Nexus
units and the bike is only 10 months old.
I'm going to be more careful next time with front brake application
but I'm curious if this is common with hub brakes.

"The Roller Brakes are probably OK for light duty use in flat terrain,
but I wouldn't recommend them for cyclists who ever go fast, or ride in
hilly terrain. It's OK for a rear brake, if you don't mind the weight, but
I continue
to be highly dubious about using it as a front brake on bikes with
full-sized wheels."

- Sheldon Brown,
http://groups.google.com/groups/search?q=nexus+brake+sheldon+brown

Quoted message said:

Is there anything
I can do to prevent a recurrence next time I go down this hill (other
than not going so fast)?

Fit a better front brake. The roller brake can stay in place if you like,
and the lever wired up to something else. The forks will take a dual-pivot
caliper if they have a hole drilled in the crown. Mudguard and wide tyre
won't be a problem for an Alhonga brake, for example (tyre is deflated
before fitting/removing wheel).

~PB

"Pete Biggs" <[email hidden]> wrote in
message news:[email hidden]...
<snip>

Quoted message said:

"The Roller Brakes are probably OK for light duty use in flat terrain,
but I wouldn't recommend them for cyclists who ever go fast, or ride in
hilly terrain. It's OK for a rear brake, if you don't mind the weight,
but

<snip>

It does seem that they are for light duty use (I'm over 100 kg and there are
many long steep hills here). The brake performance at high speed was a
surprise to me but the explanations offered of the grease
boiling/overheating makes sense, especially as the brake seemed to feel
rough and grinding at the same moment. I was pulse braking at the time this
happened so it's not a braking technique issue. The bike is already of the
sit up and beg style so short of a drag chute there's not much I can do
aerodynamically. I shall enquire at the LBS about whether a grease gun is
required to properly lube the brake or whether the tube comes with a
suitable nozzle.

Quoted message said:

Quoted message said:

Is there anything
I can do to prevent a recurrence next time I go down this hill (other
than not going so fast)?

Fit a better front brake. The roller brake can stay in place if you like,
and the lever wired up to something else. The forks will take a
dual-pivot caliper if they have a hole drilled in the crown. Mudguard and
wide tyre won't be a problem for an Alhonga brake, for example (tyre is
deflated before fitting/removing wheel).

Well actually the cheaper model of my bike comes with rim brakes but overall
the benefits of hub brakes outweigh the advantage of better rim brake
performance (in the dry) for me. What would be a really good design would be
a low drag version of a multiplate internal disc design as per motorcycle
clutches or large aircraft brakes but I don't know if such a product for
bicycle use has yet been developed or attempted. I would imagine the
sticking point would be reducing the drag/rolling friction to an acceptable
level when the brakes aren't applied. This sort of brake does offer a
compact, high braking performance arrangement however - hence their use with
large aircraft.

Thank you to all who have responded.

Paul

Quoted message said:

What would be a really good design would be
a low drag version of a multiplate internal disc design as per
motorcycle clutches or large aircraft brakes but I don't know if such
a product for bicycle use has yet been developed or attempted. I would
imagine the sticking point would be reducing the drag/rolling friction
to an acceptable level when the brakes aren't applied

Wot about disc brakes in a weatherproof cover? (or is that what you said
above?)

Paul Murphy said:

It does seem that they are for light duty use (I'm over 100 kg and
there are many long steep hills here).

Our prayers are with you ;-)

/snip

Quoted message said:

Well actually the cheaper model of my bike comes with rim brakes but
overall the benefits of hub brakes outweigh the advantage of better
rim brake performance (in the dry) for me.

If it was my bike I'd have some of the benefits of both types - by having a
rear roller brake and a front rim brake. Surely that's a good compromise?

I have ridden a bike with a Nexus roller brake. The braking power only
seemed adequate for a *rear* brake to me, and only just.

~PB

Mark Thompson said the following on 23/11/2006 10:40:

Quoted message said:

Wot about disc brakes in a weatherproof cover? (or is that what you said
above?)

Disc brakes don't need a weatherproof cover. Last weekend my whole bike
was covered in sloppy mud, but the brakes still worked well.

--
Paul Boyd
http://www.paul-boyd.co.uk/

Paul Murphy said:

I shall enquire at the LBS about whether a grease gun is
required to properly lube the brake or whether the tube comes with a
suitable nozzle.

The tube has a shaped nozzle, and the instructions show you just
sticking the nozzle in the hole on the side of the brake and giving
the tube a squeeze. The grease looks rather thin (having squeezed
some out) and heavily loaded with something black (graphite powder?
looks like it).

regards, Ian SMith
--
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"Ian Smith" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Paul Murphy said:

I shall enquire at the LBS about whether a grease gun is
required to properly lube the brake or whether the tube comes with a
suitable nozzle.

The tube has a shaped nozzle, and the instructions show you just
sticking the nozzle in the hole on the side of the brake and giving
the tube a squeeze. The grease looks rather thin (having squeezed
some out) and heavily loaded with something black (graphite powder?
looks like it).

Thanks, it looks like an all in one ready to go solution. I'll certainly
give more hub brake lube a try so I can get back to flying down hills
(although hopefully not literally). I dont like all the downsides of rim
brakes nor the cost of replacing all the bits reqd for a front disc so will
stay with the roller brakes for now with a relube every 6 months or when
reqd.

Paul