Interesting Front Brake
 

Saw this NJS vivalo up on local CL that uses what the poster calls a front coaster brake. Never seen this setup before. Kind of interesting. I would never use something like this, but I give him props for originality I guess. When posting expires, thread is dead.

http://austin.craigslist.org/bik/2103071784.html

that's just a front drum brake.

oh...i'm not familiar with drum brakes. i ride bicycles...

torker graduate 5speed has em.

they're actually pretty old school on bikes. lots of english driveshaft era cycles had em. 'coaster' is a type of drum brake.

You just haven't been riding long enough... drum brakes have been fitted to bicycle for the last 100 or so years and continue to be fitted to many models to this day... the XFD drum brake is a new Sun Race / Sturmey Archer model.

They do not have the same stopping power as a rim or disc brake but work consistently well in really challenging conditions.

Yep, just a drum brake. They're rather uncommon, but I've been seeing them lately on Trek Sohos. Apparently they're good for a commuter because they're unaffected by weather (much like a disc brake.) I'm not sure why the bike in the CL ad has one. It seems way out of place.

Actually, now I'm curious. Since disc brakes are on bikes now, why do they still make drums? What do drums have over discs?

don't disc brakes work well in challenging conditions, too? you'll have to excuse my ignorance as i don't ride anything other than road bikes. What's the advantage of a drum brake to a disc brake (other than you can apparently power lights w/ these hubs)? Also, wouldn't these make it a pain to take the wheel off in case of a tire change? And I can imagine they are heavy as hell

Either way, seems like an odd choice for a track bike, but i guess it's better than drilling the fork or uglifying it with an unsightly appendage (clamp on brake)

EDIT: was typing this up as Jake asked some of the same questions...

mud can still get on a disc. a drum is basically sealed to most contaminants, and rain and whatnot. a disc is way better than a rim, but a drum is basically inside the hub.

the disc is by far the best in terms of power and all that, but newer drums get you all the working and don't afraid of anything

A lot of people think my bike has a drum brake in the rear but it is really a generator and three speed hub... this one dates to 1964 but these too have been made for much longer than this.

Drum brakes don't generate power.

http://www.ravingbikefiend.com/bikep...vatvmudbog.JPG


Why are they still used ?

Drum brakes are less affected by weather than a disc brake and usually get fitted to city bikes and roadster type bicycles that are not ridden at the same speeds... fast stops usually require that both brakes are engaged and drum brakes were also used on tandems as a rear drag brake to regulate speed on descents.

Look at a lot of Dutch roadsters and you will see that most are fitted with drum brakes.

1975 Schwinn Speedster retrofitted with SA rear 3-speed IGH + drum brake, SA front drum brake hub. Excellent performance in wet conditions and much better power than stock sidepull caliper brakes on smooth chrome plated steel rims. In wet weather with the caliper brakes I might as well have been riding brakeless.

http://www.bikeforums.net/attachment...6&d=1291671828

http://www.bikeforums.net/attachment...2&d=1291671850

http://www.bikeforums.net/attachment...2&d=1291671806

Love drum brakes. The 90mm drum from Sturmey Archer stops better than the 70mm version. Not lightweight hubs...

Asking why anyone would use a drum brake is like asking why anyone wouldn't want a bunch of gears on their bike.
If you have to ask the question you probably won't be satisfied with the answer.

I think I would be concerned using a drum brake on a fork not designed for one.

I don't believe drum brake hubs are fork specific other than braze-ons for a cable.

Drums can be mounted to a fork without a disc tab, so there's that. They're heavy, but (as mentioned in earlier posts) high on utility and generally less expensive than discs.

There's a brake reaction arm that attaches to the fork, much like the reaction arm that attaches to the stay on a coaster brake rear hub. I probably wouldn't use one on a carbon fork, but anything made of steel or aluminum shouldn't have a problem.

It is my understanding that most NJS frames are built with forks that use a more round tube and less oval. This shape would weaken the fork for the stresses that are generated by the braking at the hub and not at the rim. Although I could be wrong.

Wrong. All types of brakes ultimately result in a maximum bending moment at the top of the fork legs where they are joined to the fork crown. The magnitude of this bending moment is determined by the actual braking force that is generated at the ground, regardless of the type of braking system. Round track fork legs have much lower bending capacity (bending section modulus) than oval road fork legs.

Short Version: I don't think a drum brake would cause the same flex as a drum brake


Long Version: i was thinking the same thing, as road bikes have ovalized fork blades to help with the forces from braking. However, road bikes generally do their braking with a caliper. I'm not sure if this is completely correct, but consider looking at a wheel from the side, spinning clockwise. applying the caliper brake at the top is almost like adding a new point of rotation, and momentum will cause clockwise rotation about the brake. this has the effect of pushing the axle/hub towards the back of the bike.

because the drum brake has braking forces in the center of the rim, there shouldn't be any backwards flex, so a round blade tube would make no difference. It also works well for avoiding drilling your fork (but it's heavy as hell)

EDIT: derp, any braking force would cause flex in the blades and would benefit from an ovalized fork. slowing is like pulling back on the fork.

Round tubes are best at dealing with a wider variety of stresses and forks are stressed in every way imaginable and in combination with each other... they are subjected to bending, compression. and torsional loads stemming from their need to support, suspend, and deal with braking loads.

Oval tubes are designed to resist more specific stresses... we apply this to our frames in order to maximize certain ride qualities and meet performance goals.

The beam on our tandems is a specially drawn oval tube, and over sized as to provide vertical load support but to also provide greater resistance to torsional loads as tandems are subject to much higher loads than a single bike.

Chain stays are partly oval because they need to offer clearance for the wheel and cranks and this does make them stiffer in the vertical plane (where they are oval) but they get drawn into round tubes which meet the dropout and have extra support from the seat stay which is typically round tubing.

And then we have these fancy new bikes with long flat tubes on the frame and fork which are there primarily for advertising space.

Wow, now that's a combo you don't see everyday :lol:

does anyone have any idea what these campy reproduction track cranks are that the poster mentions? Campy hasn't done a reissue, have they? I assume they are probably the IRD Defiants or something.

Yup... I so wantto build up a S/A drum brake bike...

You don't have to drill your sacred NJS fork crown when you use a hub brake.

The new Sturmey-Archer Dynohubs come in a drum brake/generator configuration: http://www.sturmey-archer.com/products/hubs/cid/2
http://www.sturmey-archer.com/userfi...cat/XL-FDD.jpg