Double drum brakes?

Permalink Reply by Far'arned Retrogrumpalunkus #63 on August 9, 2012 at 9:44am

One disadvantage of the disc is that the mechanicals are out there exposed to the elements. If the disc gets bent then it will be screwed up (and bicycle discs can be pretty flimsy lightweight things compared to a motorcycle disc brake. Road salt and grime can cause issues with the mechanical calipers and they can seize up.

Even hydraulic systems can gum up and seize if there is enough salt and corrosion that can happen on the sliding transfer pins that the caliper rides in and out on. I've had this happen to motorcycles with off-road disc brakes and they are more robust than the disc brakes on bicycles. Plus the hydraulic systems add another level of complexity to working on the brakes although in theory they shouldn't need as much attention. Reality and theory sometimes diverge -in theory there is no difference.

A drum brake system is pretty bullet-proof and laughs at water, freezing temps, salt, slush and whatnot. It's not impervious but it will go a lot longer without any attention than any other type of brake -especially in hard service.

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Permalink Reply by Paul on August 9, 2012 at 9:53am

I had a feeling about the grime thing, maybe save discs for a fair weather bike. I wouldn't do the hydraulic discs I'd stick with mech, I'd don't want to have to worry about fluids for my bicycle. Are drum brakes serviceable at home? I can do most anything with bike maintenance.

James BlackHeron said:

One disadvantage of the disc is that the mechanicals are out there exposed to the elements. If the disc gets bent then it will be screwed up (and bicycle discs can be pretty flimsy lightweight things compared to a motorcycle disc brake. Road salt and grime can cause issues with the mechanical calipers and they can seize up.

Even hydraulic systems can gum up and seize if there is enough salt and corrosion that can happen on the sliding transfer pins that the caliper rides in and out on. I've had this happen to motorcycles with off-road disc brakes and they are more robust than the disc brakes on bicycles. Plus the hydraulic systems add another level of complexity to working on the brakes although in theory they shouldn't need as much attention. Reality and theory sometimes diverge -in theory there is no difference.

A drum brake system is pretty bullet-proof and laughs at water, freezing temps, salt, slush and whatnot. It's not impervious but it will go a lot longer without any attention than any other type of brake -especially in hard service.

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Permalink Reply by Far'arned Retrogrumpalunkus #63 on August 9, 2012 at 10:01am

I wouldn't go so far as to say a disc is only good for fair weather -just that compared to the drum or roller brake it is more exposed to the elements. People use discs on mountain bikes with good results. But they do require a bit more cleaning/inspection to keep them going in the longer run. But not as much as rim/caliper brakes. Disc brakes don't have much of an issue with water when braking like caliper brakes do either. The forces involved with the disc brake pretty much squeeze any water out instantly. Because of the way rims are these kinds of forces really can't be used on rim brakes.

V-brakes work very well when adjusted correctly but I've found that they take a lot more fiddling to keep them centered and working properly. Dirt and grime (as well as ice/snow/freezing temps) tend to mess with the adjustment of the spring-pressure each side has so they get out of center and drag on one side. higher-end V-brakes don't do this as much (and are easier/faster to re-center) but the cheaper ones seem to get messed up pretty quickly. It seems I have to mess with the Acera V-brakes on my wife's bike every couple of rides and she rarely even rides in inclement weather. it'd be worse if she did.

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Permalink Reply by Paul on August 9, 2012 at 10:22am

I'm with ya on the v-brakes you get what you pay for. Even then, they can be fussy. I have linear brakes for winter now. Years ago I went and got myself a wheel truing stand. It helps the brakes a lot to keep the rims perfectly true, I'm sure you know this. For me, it was a major discovery.
I heard a guy at a bike shop tell a customer not to touch his brake rotor or the oil from his fingers will effect its performance. That was a real turn off to discs for me.

James BlackHeron said:

I wouldn't go so far as to say a disc is only good for fair weather -just that compared to the drum or roller brake it is more exposed to the elements. People use discs on mountain bikes with good results. But they do require a bit more cleaning/inspection to keep them going in the longer run. But not as much as rim/caliper brakes. Disc brakes don't have much of an issue with water when braking like caliper brakes do either. The forces involved with the disc brake pretty much squeeze any water out instantly. Because of the way rims are these kinds of forces really can't be used on rim brakes.

V-brakes work very well when adjusted correctly but I've found that they take a lot more fiddling to keep them centered and working properly. Dirt and grime (as well as ice/snow/freezing temps) tend to mess with the adjustment of the spring-pressure each side has so they get out of center and drag on one side. higher-end V-brakes don't do this as much (and are easier/faster to re-center) but the cheaper ones seem to get messed up pretty quickly. It seems I have to mess with the Acera V-brakes on my wife's bike every couple of rides and she rarely even rides in inclement weather. it'd be worse if she did.

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Permalink Reply by Jamais716 on August 20, 2012 at 10:58am

Anything to keep an eye out for when buying a used bike with drum brakes/internal gearing? Also, how do you change a flat??

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Permalink Reply by Casey Carnes on August 20, 2012 at 11:18am

Depends on the system, but you usually need a wrench (hex nut or allen, Shimano you can do without tools) to disconnect the shifter cable for the rear, the brake cables are usually held by tension. 15mm for the axle nuts.

Most dutch-bikes come with some heavy duty tires, Schwalbe Marathon Plus are some of the best, run these, keep up on tire pressure, and you won't have to worry about many flats.

Jamais716 said:

Anything to keep an eye out for when buying a used bike with drum brakes/internal gearing? Also, how do you change a flat??

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Permalink Reply by Gene Tenner on August 20, 2012 at 11:25am

I have drum brakes on the two front wheels of my 45 pound trike. They do not screech, unlike disc brakes. Both were similar in braking, the drums seemingly a tad better.

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Permalink Reply by Justin B Newman on August 20, 2012 at 4:37pm

When you look at the actual mechanics of how they work, disc brakes and rim brakes work on essentially the same principles. (Rim brakes are, to a degree, a really crude, simple form of disc brake). All things being equal, if touching ones brake rotor on disc brakes was going to hurt performance, it would hurt performance of rim brakes to touch the rim.

Of course, all things aren't equal... but it's my understanding that disc brakes have a number of advantages with water and/or oil on the disc. Among them, the holes on the rotor should allow water (that would otherwise build up between the pads and the rotor) to escape. On a rim, that water has no place to go ... which is one reason rim brakes suffer in wet weather.

I'm far from an expert, so I generally wouldn't contradict an employed professional, but ... in this case I think he might have missed the boat.

Then again, maybe I'm wrong and one of the real experts here will explain to me the errors of my logic. :-)

Paul said:

I heard a guy at a bike shop tell a customer not to touch his brake rotor or the oil from his fingers will effect its performance. That was a real turn off to discs for me.

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Permalink Reply by Far'arned Retrogrumpalunkus #63 on August 20, 2012 at 4:52pm

Disk brakes rotors are MUCH more solid than a bicycle rim. Therefore they can withstand a LOT more stress of being squeezed many times harder. The amount of forces being used in a disc brake are a lot greater than those employed by the rim brake caliper. To account for this the friction or stickiness of a bicycle rim brake pad is much greater than a disc brake which instead uses great force to press a less sticky brake pad against a more solid disc.

The shoe of a rim brake is stickier to compensate for the fact that it can not employ as much leverage and force without squishing the rim.

Brakeing force is equal to the square inches of contact times the square inches of braking surface contacted over a certain unit of time. This is called "swept area." A bicycle rim brake actually has a superior "swept area" over a disc brake because the rim is moving so much faster at the outside of the wheel than near the center of the wheel where the disc is* , but the disc has a much stronger surface to grip on by the disc caliper. It grips it so hard that water doesn't really make much a difference. On car disc brakes there usually are not any holes or grooves -just a smooth flat brake disc and semi-metallic brake pads usually using sintered pieces of steel in it to give extra grip or sometimes an organic compound to give it more sickiness (such as the rubberish compound in bicycle rim brake pads)

But my point is, before I started to ramble, is that because the rim of the rim brake is only good for a limited amount of squeezing force the brake shoes need to be WAY more sticky -but when you add water to this it really changes the friction. A disc (or hub) brake uses a TON more pressure and the pads are not very sticky at all. Adding water to that friction zone doesn't change the brake's ability to stop very much at all -and the water is soon pushed away by the very much greater forces involved squeezing a really solid object rather than a squishy hollow bicycle rim.

*some motorcycles and race cars have experimented with disc brakes that are at the outer portion of the wheel (by the rim) rather than at the center near the hub. This greatly increases brake swept area and overall feel and braking, as well as helps with cooling. But on most brakes this is just way over-kill. Also a big round brake disc weighs more and adds more rotating mass at the outer area of the wheel.

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Permalink Reply by Tony Adams on August 20, 2012 at 8:26pm

I'm just completely guessing, but I wonder if discs might make a bike more attractive to thieves than drums?

Paul said:

Ha! Now I'm thinking of a frame to weld'em on. I'll stick with drums for winter. Discs do sound better than I was thinking.

Casey Carnes said:
I've never noticed much of a difference between wet and dry performance. Usually the tires are the weakest link when its wet out.

If you have a frame you're fond of, You can have disc tabs installed by a framebuilder for maybe $100. Drums probably are the better option if you are more worried about zero maintenance and supreme reliability and weight isn't a big issue.