E-bike Brakes thread, please add what you know

[Chalo]

how does a (good) drum brake compare to a (good) rim and (good) disk brake?

On a full-sized wheel, a drum brake typically offers less braking torque than a comparable quality rim or disc brake. It is more consistent in all weather conditions, though. Traditional drum brakes like Sturmey Archer take many hundreds of kilometers of use before they are fully run-in and ready to deliver their best performance. But they do not need pad replacements for tens of thousands of km. Sturmey Archer drums are available in standard 70mm diameter and oversized 90mm diameter. The larger drum yields more braking power and improved heat dissipation, just like a larger disc rotor.

Traditional drum brakes don't narrow the hub flange spacing as much, or create as much spoke offset, as discs do. That allows drum braked wheels to be stronger than disc wheels, like for like. Drums can be laced to normal rims or "disc only" rims.

Shimano Rollerbrakes are a kind of interchangeable drum that attaches to the outside of a splined hub. They use steel shoes running in grease lubrication-- more like a coaster brake than a traditional drum. The latest generation IM80 and IM81 Rollerbrakes are particularly powerful compared to other drums (and they have huge finned heat sinks), but still have the characteristic gradual lever response of a drum brake. I use one on a heavy, long wheelbase bike with strong rear weight bias, and it skids the rear wheel with ease under my 145kg of body weight.

Front Rollerbrakes have a built-in torque-limiting feature that is described as anti-lock (but is only a force limiter, with no feedback mechanism). I won't use a brake that limits its own power, but the rear versions don't have the problem feature.

 

[MadRhino]

...all the tandems that I have personally seen out in the real world were ridden on the street with a female on the back.

Well, I'd rather ride a tandem with a female on the front, that is if she'd have a fair size bum of course.
On the other side... On a single with passenger seat, I prefer to have her behind on the bitch pad

 

[izeman]

Any brake that will skid the rear wheel, or tip the bike up if used in the front, has all the braking power it is physically possible to use.

that's correct if you add: AT THE WANTED MAXIMUM SPEED. a brake that makes the front wheel lock at 20km/h may be too weak to stop a bike at 50km/h. and that's the point. i think EVERY perfectly adjusted brake is sufficient for regular human powered bikes. but we're talking about "bikes" that go up to 80mph/130km/h. my bike does 40mph/65km/h and i need all the brake power i can get. that said my 203mm hydraulic disc brake in the front, and 160mm at the rear with regen braking is just "ok".
kinetic energy is squared when speed is doubled. so 40km/h needs 4 time the stopping power then 20km/h. 80km/h needs 16 times the stopping power of 20km/h.

 

[llile]

Well, all this Chevy-vs-Ford rim vs disk brake discussion is interesting. Personally, I am done with rim brakes and set on using disk brakes of any stripe.

But what about motor cutout on the brake levers? I have used two e-bikes, one with brake cutout and one without. Although I am perfectly capable of releasing the throttle and braking at the same time, I have had throttle failures where the motor stuck on full tilt. The brakes *theoretically* can overpower the motor on my old bike, but it was a helluva ride up to that first stopsign before I could reach the Controller OFF switch. I decided that brake cutoff was a safety feature in case of a failed throttle. New bike has more powerful motors (two of them!) so maybe the brakes could overpower the motor, maybe not?

Brake cutoff has other advantages. I have a "parking brake" on my bike, basically a length of velcro that allows me to lock the brake when parked. This has proved really handy when loading up groceries on a hill (that is all I do on hills, besides ride up them, I am not one of these kamakazi downhill racers) but it also prevents a klumsy touch of the throttle from sending the bike racing off. If I let someone else ride my e-bike, I leave the parking brake on while I give them a once-over of the controls, so they don't say "Twist the throttle, you mean like THIS?" and zoom off. I'll lock the brake when working on it, so I don't accidentally zoom across the shop (ask me how I know this happens)

Since the stuck throttle thing is a real possibility (I had a broken ground wire, making the signal from the throttle always 5 volts - zoom!) I have decided that E-brake-cutoff is a necessary feature on a powerful e-bike.

 

[spinningmagnets]

I'm now embarrassed that I didn't include drum brakes in the initial posting (googles furiously, scratches chin, reads, reads, reads..)

I was searching for reviews of drum brakes, and surprisingly I found a couple on a mountain bike forum. I believe that has got to be one of the most demanding applications, so it would likely reveal any limits to the best designs, and also some comparisons from riders who have used both discs/drums on the same downhill course.

http://forums.mtbr.com/brake-time/sturmey-archer-drum-brakes-anyone-138059.html

"...The feel is unlke any other brake I have used. Different. But good...It feels a bit like power assist. So instead of requiring increasing force as you approach lockup with say, cool-stops on sidepulls, as you stretch the cable taut and torsion the brake arms, the repsonse is uncannily linear...[braking is]...relatively easy for someone with low hand strength...The 70 mm may have been just fine...But for the potential to be undertaxed and last decades, well, I could not resist [the 90mm].

"...I have ridden with it snowing and not, sub freezing, and today in the rain. As promised by a brake system [that is] tucked out of the weather, there is no difference in braking under any weather conditions I subjected it to, so far..."

"...After a muddy 24 hour race a few years back, I ran out of disk pads and had to retire. I figured there had to be a better way. I used to get good performance out of drums on my motorbikes many years ago, so I tried them on the bike. The first picture is a bike I used in the next muddy 24 hour race (70mm drums). The braking performance was better than adequate but not brilliant, and after the race my forearms knew all about it. However, any time I lost to not having optimum braking was more than made up for by: the time not lost by changing my disk pads 4 times or more [during the race]...There were no issues with the brakes throughout the race, no adjustment was needed. When I finally checked the brakes [after the race] they were clean inside and hardly any wear at all. My conclusion was that the front brake could do with more power, and the back was ok [with the 70mm]. Then S-A introduced the 90mm front brake, so I fitted it to this bike. The 90mm is more powerful and very close to being good enough to replace a disk fulltime for my use..."

Firstly cables - any compression in the outer is a no-no. I reckon using something like Avid Flak Jackets with the steel tubes would improve things amazingly.

Secondly concentricity - in my motorcycling days I would have had them [the brake shoes] mounted on a lathe and the linings matched to the drum. I may do this with the 90mm because I'm sure there's lots more stopping power in there.

Thirdly linings - these brakes are aimed at the cruiser and industrial bike market, so the linings are appropriate to that. Linings with more friction would improve power. I used to fit green Ferodo linings to the motorbikes (that I raced) and that was capable of doing stoppies with drums back then, but I don't know what the modern equivalent is. If I can find it, then I'll be using it.

The outstanding thing is the value for money. You can buy the [drum brake] hub for about the price of 3 sets of premium brake pads and it will outlast a disk fitted with them...

 

[Chalo]

Any brake that will skid the rear wheel, or tip the bike up if used in the front, has all the braking power it is physically possible to use.

that's correct if you add: AT THE WANTED MAXIMUM SPEED. a brake that makes the front wheel lock at 20km/h may be too weak to stop a bike at 50km/h. and that's the point. i think EVERY perfectly adjusted brake is sufficient for regular human powered bikes. but we're talking about "bikes" that go up to 80mph/130km/h. my bike does 40mph/65km/h and i need all the brake power i can get. that said my 203mm hydraulic disc brake in the front, and 160mm at the rear with regen braking is just "ok".
kinetic energy is squared when speed is doubled. so 40km/h needs 4 time the stopping power then 20km/h. 80km/h needs 16 times the stopping power of 20km/h.

It is force that tips the bike, and power that burns off velocity as heat. Discs win in terms of braking force per lever force. They lose in terms of maximum braking force. They lose big time in terms of braking power and energy dissipation before failure. It's a simple matter of rotor physics. You'll warp your rotors, boil your hydraulic fluid, and/or melt plastic and rubber components of your disc brakes well before a rim brake on a heavy aluminum rim reaches its limits.

You don't know these latter things, and you'll never have to know. All you know from personal observation is that discs feel stronger when you give them a little squeeze. That's because you're simply not big enough, and your bike not long enough, to test your discs beyond their limits of force, power and energy dissipation. Even motorbike type speeds on an e-bike are just not all that energetic compared to high mass times significant elevation changes. The faster you go, the more aero drag helps your brakes slow you down. You are arguing for discs on the precise points where they are most inferior to rim brakes-- power and energy. If your reasoning goes, "my hands are weak and they tire very quickly, so I have a difficult time stopping from high speeds", then that is a point on which disc brakes offer a real advantage.

Motorbikes have massive powerful brakes not because they have to stop from high speeds, but because they have the power to speed back up and do it over and over again in a very short span of time, without allowing the brakes to cool down adequately between stops. Bicycle disc brakes are an even worse choice for such duty than bicycle rim brakes, because they have less thermal mass to absorb heat and less surface area to discharge it from than either rim brakes or motor vehicle discs. Just about everyone who uses discs or drums knows about brake fade. You know what kind of brakes don't get hot enough to fade? Rim brakes. Fade is just not an issue for rim brakes, because they don't get nearly as hot from the same energy input levels that fade discs.

For as long as there is a motor cult, there will be some motor cultists who favor disc brakes on bicycles for reasons other than their actual virtues, who swear discs are better because they are discs, and discs are better. (When and if motor vehicles switch to magnetic brakes, those folks will then decide that only magnetic brakes are adequate for their "extreme", "hardcore", "intense" cycling.) And of course there will remain some specialty applications that require disc brakes or other hub brakes for their actual virtues. But rim brakes will never be superseded, because it's plain good engineering to do two jobs with one part (the rim) that you must have anyway.

 

[full-throttle]

Fade is just not an issue for rim brakes, because they don't get nearly as hot from the same energy input levels that fade discs.

Are you serious? :lol: That just proves that you have no idea what you're talking about.

Discs can get to much higher temperatures than rubber pads.

 

[izeman]

Fade is just not an issue for rim brakes, because they don't get nearly as hot from the same energy input levels that fade discs.

Are you serious? :lol: That just proves that you have no idea what you're talking about.
Discs can get to much higher temperatures than rubber pads.

+1. and it's absolutely NO problem to overheat a rim brake. done that several times. and you REALLY don't want that.
i have no idea why chalo needs this rim versus disc discussion. each one has advantages and disadvantages. but you simply can't stop evolution.
and PLEASE stop arguing with disc mass for absorption of heat. this is b***shit. a thinner disc will heat up faster and will COOL down faster as well.
chalo stay with whatever brakes you like. you may even favor beltbrakes

or one of these. a STEMPELBREMSE - no idea what the english term for that is

i'm fine with that. what please stop this USELESS discussion.

 

[izeman]

...But rim brakes will never be superseded, because it's plain good engineering to do two jobs with one part (the rim) that you must have anyway...

what about putting a big stick through your spokes while riding??? no fading, 100% braking power, no extra parts other than the stick needed. now i'm really happy that i found a good use for my master in technical engineering.

 

[full-throttle]

He won't stop. He's just a troll that believes scaled down motorcycle technology makes bicycles less enjoyable to ride. :lol: cuckoo So he chooses to promote inferior solutions. Prob been kicked out from every other forum until he found a retreat here.

It's been already discovered he has not experienced good disc brakes, so all his posts are just a bunch of biased opinions. Now that he wrote rim brakes don't fade, I would find it hard to believe he ever ridden down a steep long hill

 

[Toorbough ULL-Zeveigh]

it's plain good engineering to do two jobs with one part (the rim) that you must have anyway.

a good engineer wouldn't say that because that's not what engineering is about.
he would say that it's good for which application.

the Lotus/British school of engineering was that if you didn't design one part to do at least three jobs or preferably four Colin Chapman would have you fired.
his way of doing things made for very very light nimble cars that quit working & fall apart whilst sitting in the garage.
even thermal expansion & contraction will throw things out of position & are a pain in the ass to align/adjust/repair as things wear out because in trying to correct one you screw up the other three at the same time.

mercedes/german perfectionist engineering is everything must be single part for single function.
you wind up with a very heavy if not bloated (S-class probably the best example) but very solid vehicle that can travel for hours at over 120 kph on die bahn without breakdown as mandated in law by TUV or whichever body regulates that.

so who is the better engineer?

is it better to be short or tall?
you can't be both at the same time.
that's why the good engineer asks, 'better for what?'.

this constant Mary go round the roses is pointless.

 

[rscamp]

Ya. I was wondering why no one had mentioned drum brakes until recently. Sure, they aren't as efficient by weight and fade more than disks, but they have some real advantages like the long life and weather resistance mentioned above.

Here are a few other advantages. The large OD of the hub reduces spoke forces from the torque of hard braking. The exposed lever makes it easy to add a reed switch sensor for brake light/cutoff. And last but not least, I think they are quite attractive and give a bike or ebike a very solid look.

 

[knighty]

I'm surprised there's no guides to diy ebrake cut offs....

(I need to add some to my bike)

 

[spinningmagnets]

Reed switches for an ebrake cutoff
http://endless-sphere.com/forums/viewtopic.php?f=16&t=11760

 

[izeman]

Reed switches for an ebrake cutoff
http://endless-sphere.com/forums/viewtopic.php?f=16&t=11760

or here http://endless-sphere.com/forums/viewtopic.php?f=3&t=38848&start=25#p691975
this i how i did it. it's a bit of work to find the correct position for switch/magnet, but it works nice.

 

[llile]

Reed switches for an ebrake cutoff
http://endless-sphere.com/forums/viewtopic.php?f=16&t=11760

or here http://endless-sphere.com/forums/viewtopic.php?f=3&t=38848&start=25#p691975
this i how i did it. it's a bit of work to find the correct position for switch/magnet, but it works nice.

Nice hack, but you can alsojust buy one. Not that hacking something you can just buy isn't totally worth it, I do it all the time, but just in case other folks might not know this.

 

[Chalo]

Fade is just not an issue for rim brakes, because they don't get nearly as hot from the same energy input levels that fade discs.

Are you serious? :lol: That just proves that you have no idea what you're talking about.

Discs can get to much higher temperatures than rubber pads.

And yet in practice, those elevated temperatures cause disc brakes to fade, while rim brakes just don't.

The best you can say in discs' favor is that discs usually recover from heat fade after they cool down, while many rubber rim brake pads harden from repeated heat cycling. (At least they are cheap, standardized, and easy to replace.)

Apropos this discussion generally-- the day before yesterday,, a customer brought his expensive Specialized MTB in with zero brake action on the rear hydraulic brake. Nothing. If it had been a cable brake, I'd have sorted it out on the spot in minutes and charged him six dollars. And his brake probably would not have gone straight from normal operation to zero all at once. As it was, he had to leave his bike for scheduled service and pay $20 plus the cost of proprietary hydraulic fluid to get going again. That's not a back-breaking difference, but it's an added cost in cash and downtime for no practical benefit in return. There was not an obvious leak in his system, but whatever caused the earlier failure might well cause his brake to fail again soon.

 

[full-throttle]

And yet in practice, those elevated temperatures cause disc brakes to fade, while rim brakes just don't.

Rim brakes fade too you troll. At much lower temperatures than discs. Lets say 80degC vs 200degC or there abouts.
Discs have smaller surface area, but running hotter enables them to shed more energy than at rim brake temperatures. Fourier law.

 

[Chalo]

Discs have smaller surface area, but running hotter enables them to shed more energy than at rim brake temperatures. Fourier law.

You disregard the effect of discs' much smaller surface area and much lower thermal conductivity. The proof is in the temperatures themselves-- if they could shed heat as fast as rim brakes, they wouldn't be able to get smoking hot to begin with. The only rim brakes that ever get smoking hot are those with wooden rims that can't carry away heat like metal.

 

[knighty]

Nice hack, but you can alsojust buy one. Not that hacking something you can just buy isn't totally worth it, I do it all the time, but just in case other folks might not know this.

I've tried a few off the shelf ones, but most of the leavers stuck balls

my avid leavers are much better - more cable movement for the same amount of lever travel

 

[knighty]

Reed switches for an ebrake cutoff
http://endless-sphere.com/forums/viewtopic.php?f=16&t=11760

thanks for that, ordered 6 reed switches on ebay, 2 each for 2 bikes and 2 spares

bought changer over ones, so I can make them work break lights too

 

[full-throttle]

Discs have smaller surface area, but running hotter enables them to shed more energy than at rim brake temperatures. Fourier law.

You disregard the effect of discs' much smaller surface area and much lower thermal conductivity.

No I didn't. Highlighted just for you troll.
What does conductivity has to do with conventional heat dissipation?
BTW by saying that you are contradicting your own story on the previous page:

Funny, though, if it happens because the hot disc rotor cooked some oil out of the hub's axle bearing grease.

So for a disc to be able to cook[sic] some oil from a axle it must have an exceptional conductivity. It has to heat up an aluminium hub, transfer the heat through bearings etc.. :lol:

And talking about making up stories - next time you are cornered in you flawed argument and come up with some imaginary scenario, you're better to have some evidence to support it. A video would do.

Apropos this discussion generally-- the day before yesterday,, a customer brought his expensive Specialized MTB in with zero brake action on the rear hydraulic brake. Nothing.

How convenient. So, what happened - was it a result of a crash or he accidentally cut the line trying to remove a zip tie? And you don't mention how often you see a brake cable fail

 

[swbluto]

Discs have smaller surface area, but running hotter enables them to shed more energy than at rim brake temperatures. Fourier law.

You disregard the effect of discs' much smaller surface area and much lower thermal conductivity. The proof is in the temperatures themselves-- if they could shed heat as fast as rim brakes, they wouldn't be able to get smoking hot to begin with. The only rim brakes that ever get smoking hot are those with wooden rims that can't carry away heat like metal.

Indeed. Also, it seems everyone is ignoring thermal mass, which is really the most important factor at play in normal use. The sheer quantity of metal in a rim is much higher than in conventional discs, so it can hold more thermal energy without increasing too much in temperature.

 

[full-throttle]

I was wondering why no one had mentioned drum brakes until recently. Sure, they aren't as efficient by weight and fade more than disks, but they have some real advantages like the long life and weather resistance mentioned above.

Drum brakes seem like a very nice alternative. I personally like the look of them.

On the other hand they are uncommon, cost more (especially considering a wheel build) and not available on hub motors.

 

[briogio]

I can't believe nobody's brought up Magura hydraulic rim brakes. I came from a motorcycling background and they just made sense to me right away. I raced and distributed them in the early '90's in Eastern Canada. There is no arcing of the regular rim brakes they go straight on like a disc. They're a sealed hydraulic system using basically mineral oil. Magura are a German company who have been making motorcycle brakes for years, they turn your wheel into a 26" disc, easily crush through snow, mud water, don't fade, excellent modulation, pad choice, quite cheap and simple (all the trials guys use them, for good reason). IMHO these are the best bicycle brakes by far and if your really anal you can plasma/ceramic coat your rims!