Shimano Roller Brakes

[alicat]

To change the subject slightly, I have a Giant Expression N3 and am thinking of upgrading the Shimano Nexus 3 gears to Nexus 7 because the existing bell crank needs replacing and I have hankered after a bigger gear range for some time.

Will the existing roller brake BR-1M31-R work with the new hub SG-7R50? Money is a concern at the moment so I will probably hold off if the answer is no.

Thanks for any help.

[Ayesha]

a half-size wheel with the same hub brake is like having a disc brake upgrade to a disc twice the size.

Standard discs are 160mm. Seen many 320mm discs?

Imagine how powerful they would be....

cheers

Dissagree.

Brake rotors and their friction areas are matched against the mass inertia of the vehicle. Reducing the circ' of the wheel will only reduce the vehicle's mass a little, so the braking effectiveness would be similar.

A Sachs Torpedo in a 26" wheel fells JUST LIKE a Sachs Torpedo in a 14" Mini Moulton wheel.

When I'm riding the bikes, the lower mass of the Mini Moulton makes little difference to our rolling inertia

[Brucey]

Re disc brake disc size vs wheel size; you can disagree all you like but it is simple physics I'm afraid.

A Sachs Torpedo in a 26" wheel fells JUST LIKE a Sachs Torpedo in a 14" Mini Moulton wheel.

there is a very good reason for that. Can you tell what it is?

cheers

[Nettled Shin]

Dissagree.

Brake rotors and their friction areas are matched against the mass inertia of the vehicle. Reducing the circ' of the wheel will only reduce the vehicle's mass a little, so the braking effectiveness would be similar.

I'm surprised at you writing this. When you are in one of your lucid phases, you normally speak sense. Why not "think again", as Johnny Ball might have said?

[[XAP]Bob]

Smaller wheels, or larger discs, increase the linear speed of the disc through the caliper - hence increased effectiveness

[Brucey]

it is not the speed that is the issue; it is the force that is generated by the caliper, and how the resultant torque generates a retarding force between the tyre and the road.

If speed were the issue, the retardation would vary with road speed for all brakes, and it doesn't.

Speed through the brakes does affect the capacity of the brake to do work at a given force, but that is a different thing.

cheers

[jb]

Does anybody know if the grease in fact increases braking efficiency i.e. acts acts like lubrication in friction drives where the lubricant becomes solid under pressure.
I fitted a roller break recently and it was OK but after a long steep descent it has become very poor. There is no disernable wear apparent so I can only think that it has boiled the grease off.

[MartinC]

My experience is that on the couple of occasions I've run a roller brake dry (long descents and overheating) then the braking has been very poor i.e. they seem to brake better with grease in them.

[Mick F]

Yes, deffo.
Grease them, I use normal grease.

The roller brakes I have are in 27" wheels and don't seem to be too fussy, but a few years ago I "borrowed" the front one to fit into the Raleigh Chopper. Having it in a small wheel increased its efficiency many fold, but it also became very fussy about grease.

Without it, or at least if it went dry, it would snatch terribly also grind and make strange noises. Grease it up and it was superb.

[jb]

Thanks both.
I have some of Shimano's 'special' grease on the way, we'll see if it improves matters.

[cycle tramp]

Has anyone actually worn out a shimano roller brake yet?

[Brucey]

not personally, but I have seen it happen. Much use with not enough grease will do it.

It seems that whilst a lack of grease is quickly betrayed by various foul noises under heavy braking, gentle braking does not make noises that are sufficiently gruesome to cause normal folk to go to the bike shop and have grease added. In the meantime the brake is wearing, a little and often, and will wear out in a year or two of such daily use.

Given the choice of 'no grease' or 'the wrong grease' I'd say that anything is better than nothing in this case.

cheers