crhilton

I'm not an expert, not even a great rider.

It can't lock unless you squeeze it hard enough to do so. You're not supposed to lock it, you're supposed to barely not lock it. But the ability to lock the wheel indicates that the brake has maximum stopping power: It can't do anything more than lock it.

And if you can lock and unlock your wheel quickly you can theoretically achieve a faster stop. This is due to the fact that the coefficient of static friction is always higher than kinetic friction (that's probably the wrong term). This is why ABS brakes work (at least until they get too hot and malfunction).
On a bike you do have the added problem of a very high center of gravity.


Incidentally, it's also heavily dependent on road conditions. Maybe I've only had lock ups on smoother pavements? I'm not thinking of ice, I know your front wheel can lock on ice; otherwise I can't imagine how you get stopped.

matthew_deaner

I don't know... I've always wondered about laws requiring front brakes to be capable of "locking". It seems to me like you're getting max breaking power when the back wheel rises off the ground and you're throwing your weight back on the bike. Locking the front wheel would result in a loss of breaking power. I could see a front wheel locking on ice (of course) but I've been riding for a long time and I have yet to experience a front wheel lockup.

This gives me perspective on the whole disc vs. rim brake debate. I can achieve max breaking power with rim brakes, obviously, because I can lift the rear of the bike off the ground. So when riding in dry conditions, I really can't understand why disc brakes would be an advantage. Of course, when it's wet out disc brakes rule.

K6-III

For a commuter bike, the much rarer DRUM BRAKE makes more sense.

Take your existing caliper bike and have the front wheel rebuilt with a Sturmey Archer XFD drum brake or XFDD dynohub/drum brake.




Assuming your existing rim is a 36 hole, should be an easy swap, with near disc braking performance, brake pads that last nearly forever, are less affected by wet weather than a disc, and allow for stronger, dishless wheels, while working with your existing non-disc fork.

CdCf

Drum brakes have piss-poor modulation. It's on or off, really. And they're far from a disc brake in terms of performance.

matthew_deaner

I'm not trying to hijack this thread... but that drum brake/dynohub might be what I'm looking for. And I wouldn't have to replace the fork on my Rob Roy to install it. Do you have firsthand experience with this brake? If so, how does it compare to disc brakes? And where can I buy it? Does it use standard road levers?

markhr

Agreed

Have you ever used them? More importantly have you ever used bedded in disc brakes?

As should we all.

Incorrect

They're less expensive and MUCH less complex than rim brakes of similar quality. They do however add marginal amount of weight both at the hub and brake unit.

Incorrect. No UCI decision has been made regarding their use for non MTB events therefore they cannot be used. Disc brakes have not been banned.

Agreed

Agreed

markhr

Incorrect. If that was the case then they'd be banned from MTB events with mass starts. As stated earlier the UCI has made no decision regardiong their use outside of MTB events therefore they cannot be used. They have not been banned.

matthew_deaner

No decision = ban. The same in effect. Why is this such an important issue for you?

matthew_deaner

Yes. I used to have an MTB with disc brakes. I also test rode several disc-brake equipped bikes when shopping for a commuter.

markhr

Have you ever used disc brakes? If so you'd find that they're very easy to lock up should you choose to, i.e., no grabbing like crappy rim brakes.

Agreed

All opinions deserve to be heard, even the most misguided. It's called freedom of speech.

As long as they lock the wheels up I doubt any specific brake type will be legislated for/against by local government/councils. The UCI is a completely different story though as I'm sure you're aware.

K6-III

I have both the XFD and the XFDD. The dynohub works as you would expect. The brake performance is good provided you do the following:

1. Only use short-pull break levers (no v-brake levers)
2. Do not use the included pre-fab brake cable, as brake performance is very mushy with the long cable.

For road levers, you'd have to use a traditional road-specific brake cable, not the MTB-style cable included with the hub. If you have any other questions on the drum hub, send me a PM and I'd be glad to help.

As for brake performance with the Sturmey Drum brakes of today, they definitely outperform caliper brakes in the dry, and significantly in the wet, if the cables are adjusted properly and once the pads have broken in (takes a few weeks of riding, don't forget to tighten barrel adjuster for first few weeks). The whole point of the drums is that they make no compromise on wheel strength as do Discs and don't require disc-specific forks/frames.

markhr

Given how quickly rim brakes wear out rims, especially in mixed conditions, rim replacemnt will always be the most expensive and frequent headache.

markhr

110% agreed - if it can't stop in the legally mandated distance then it shouldn't be on the road. There should also be two means of braking, i.e., 2 discs, disc and hub, 2 hubs, disc and fixed gear, etc., so it's doubly redundant.

markhr

Even with crappy rim brakes you should be able to lock up the brakes just by squeezing as hard as possible? It's easier with disc brakes but so is modulating the braking so locking up is purely rider choice and not due to grabby brakes.

markhr

ABS works by pulsing the brakes against the moving braking surface. i.e., there is no static contact until the wheel/braking surface is at rest. They were invented to prevent skids and mimic the brake foot pedal pumping action used by experienced drivers when slowing either quickly or in poor conditions.

Sixty Fiver

My primary commuters(fixed gears) both run a single front brake that is not a disc.

Having enough stopping power has never been an issue.

markhr

Are they available in a quick release version?
Are they available in a cassette(8,9,10 speed shamino and campagnolo) version?
What happens when the braking surface (not the brake pads) wears out? Do you have to throw the hub away?

markhr

They may have a similar effect but they are not the same. It's important to me because rim brakes suck and should be replaced a better means of braking a.s.a.p.

markhr

so how can you state that there are no absolute truths with disc brakes? Were you leaving this as vague as possible (your no absolute truths comment) just to create an argument?

CdCf

Perhaps, then, it never rains there. Rim brakes suck massively when it's wet. And even if they provide perfect power in all instances, the fact that you brake by wearing down a structural part (the rim) is so absurd that it's insane! And the wetter it is, the worse the wear. I'm halfway through a pair of pads after only about 250 miles of city commuting and a couple of medium-distance rides.

K6-III

There is no cassette version, but Sturmey does make the 7 speed freewheel drum brake hub, the XRD. Otherwise, the same brake is available in 3, 5, and 8 speed internal gear hubs.

As a set of drum brake pads can last 10-20 years of consistent use, with minimal effect on the braking surface, there shouldn't be too much cause for concern. Should you want to replace drum brake pads, J&B stocks them, so any bike shop that orders from J&B should be able to get them.

matthew_deaner

No absolute truths - only opinions (except for wet weather performance, where disc brakes are clearly superior, and I mentioned that). People use their equipment differently. People have different needs and expectations, different priorities. You have your opinions, and I have mine. Shouldn't we both be able to air our opinions in an environment that is free from oppression and verbal attack?

markhr

Thanks very much for the answers.

markhr

Agreed


...now where did I put my ammunition bucket of rotten fruit and eggs

Sixty Fiver

CdCf - Your rim brakes might suck massively when it's wet... I really have no concerns about my ability to stop in the rain or in the middle of our Canadian winter.

The amount of wear on my fixed gear bikes is far less than what I experience on my multispeed bikes since I use the brake less and because I always ensure that things are kept squeaky clean and serviced.