E-bike Brakes thread, please add what you know

spinningmagnets

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I went to look up something on brakes, and the ES wiki doesn't seem to have anything. I'm no expert, please add what you know and after a while someone will sort through this thread and write a brakes section for the wiki...

Here's the requisite "Sheldon Brown" link: http://sheldonbrown.com/cantilever-adjustment.html

Antique Spoon Brake (only added to make this thread easier to find in the future)

BrakeSpoon.png

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Side-pull

Used on childrens bikes and also the lowest-end adult bikes. These are the least desirable type to use on a powered bike. Some newer road-bikes have begun using a much higher quality side-pull (shown in pic) simply because of the compact size and their light-weight.

brakes-calipers-campagnolo-super-record-2011-sketelon.jpg


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U-brakes

Rarely used for a long time, recently making a comeback on freestyle BMX rear wheels. The pivots are above the pads, and each arm has its own return-spring. Normally mounted very low, just behind the bottom-bracket.

ODYSSEY%20EVOLVER%20U-BRAKE.gif


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Direct-pull / linear-pull cantilever

Shimano has trade-marked the name "V-brakes" for this style, even though the "center-pull" cantilevers (shown farther below) are the style that actually look like an inverted V. Very common and affordable, performance is not bad. I like how it is VERY easy to disconnect/reconnect the cable with no tools so a bike can have its wheel taken off for transport, or fixing a flat. Each arm has its own individual return-spring, with return-tension being adjustable.

pict_linearplbrk_f.gif


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Center-pull (traditional) cantilevers

Pros: The mechanical advantage is adjustable on some styles.
Cons: Arms protrude outwards

Bike-brakes.jpg


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Mechanical (cable-pull) disc drakes

Popular for the front brake of any application that is sometimes more severe than average...if you are in a situation where you are likely to bend or ding a rim, any style of rim brake might make that bad situation even worse. Avid-BB7's are popular (shown in pic), and a frequently mentioned reason is their easy knob-adjustment of the pads with no tools needed.

Many posters seem to feel that a quality rim brake system is as good as any well-made cable-pull disc brake. For ultra-high mileage riders, a disc is cheaper and easier to replace from wear, compared to replacing a worn rim, but this is not a concern for most riders.

avid_bb7_08_m.jpg


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Hydraulic disc brakes

Pros: Very high braking possible with a very adjustable modulation of "feel". Hydraulics are sealed, compared to cables, which can be negatively affected by water and mud.

Cons: Expensive, requires more frequent maintenance and adjustment.

My initial search indicates that Hayes, Formula, and Avid seem to be popular right now. A cheap hydraulic system is not as a good as a great cable-pull disc system....however, high-end hydraulic systems are widely reported to perform very well in extremely demanding applications.

hayes-stroker-ace-4-640x428.jpg


edit: experienced ES member MadRhino recommends Magura Gustv M hydraulics http://endless-sphere.com/forums/viewtopic.php?f=3&t=58800#p877883

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Drum Brakes

Fully enclosed against the weather. Although they are lesser known and rarely used, recently improved versions perform very well. Sturmey-Archer versions available in the common 70mm diameter, and also the larger 90mm version. Some testimonials indicate that drums can handle high brake heat on long downhills exceptionally well due to the mass of the aluminum that is integrated into the drum and rim.

5568160357_f0710361c6_z.jpg


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Direct-Drive (DD) hubs, when used as a magnetic brake

Regerative braking (Regen) is when a hub is temporarily no longer powered, and instead it is electrically configured to act as a generator rather than a motor (the electrical re-routing is done by the controller). This will put some watts back into the battery (but usually very little). Even if the amount of watts harvested is very low, regen can be very valuable as a braking tool.

When you use regen as a brake (regardless of any harvesting of watts), the bikes' normal brakes stay cool, which can be very important to a heavy cargobike on a long downhill. Regen/Plug-braking is unaffected by splashed-water/rain/mud.

A device called a "plug brake" can be cheaply and easy made by wrapping resistor wire in a coil and attaching a switch on the brake handle to activate it. The spinning hub motor will cause the plug brake to get hot. It will not harvest watts back into the battery like regen, but it will still act as a magnetic brake. It can also be designed to be adjustable, if desired.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=10422#p170905

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spinningmagnets said:
Mechanical (cable) disc drakes

Popular for any kind of downhill MTB frame because..
We haven't used mechanical disk brakes on DH and Freeride bikes for over a decade, and that was a major improvement.

Brakes have been discussed so many times, it should be easy to find all the info.
 
We haven't used mechanical disk brakes on DH and Freeride bikes for over a decade, and that was a major improvement

What are the performance benefits of hydraulic brakes? I believe they must perform better for so many to use them in high-end applications, but I am unfamiliar with them. What are the top three brands?

I will be reading a lot about brakes this week, but just because a poster makes a bold claim, I don't know if their information is trustworthy. From reading your posts in the past, I believe you are actually experienced and I would appreciate any info you could provide.

edit: dual cable on one brake handle https://www.endless-sphere.com/forums/viewtopic.php?f=3&t=29902&start=100#p453652

4 pages "brakes discussion" http://www.endless-sphere.com/forums/viewtopic.php?f=1&t=48946
 
I have Hayes Stroker on my 50+ mph Giant DH Team and personally could not imagine anything but a big 4 piston hydraulic caliper with a minimum of a 203 mm rotor to slow me down from those speeds. If you look into the motorcycle/scooter world which we are basically building anything over 30mph is hydraulic. While mechanical disks are similar the need to constantly monitor and adjust to only save a few bucks for me seemed senseless. I'd be afraid my A.D.D. would get the best of me and I'd forget to pay attention to them. I will tell you that the hydraulic brakes can be dangerous. Grab to much of the front brake in an emergency situation and get ready to kiss the concrete! It's all I will ever use for me or mine.
Tom
 
Thanks! Recently Kepler posted that he had changed his front disc to a smaller 180mm diameter, because it actually stopped too well with the largest diameter 203mm disc that he had originally chosen. http://endless-sphere.com/forums/viewtopic.php?f=6&t=47139&start=175#p717187
 
litespeed said:
I have Hayes Stroker on my 50+ mph Giant DH Team and personally could not imagine anything but a big 4 piston hydraulic caliper with a minimum of a 203 mm rotor to slow me down from those speeds.

Multi-piston hydraulic brakes on bicycles are a tribute to motorcycles rather than any kind of important or beneficial feature. As you point out, hydraulic brakes with especially strong lever response must be used carefully and can cause crashes. What they can't do is make you stop in a shorter distance than properly working rim or mechanical disc brakes. It's just like power brakes versus non-power brakes in a car-- they just make the pedal easier to push; they don't necessarily mean stopping distance will be shorter. In fact, the unpowered brake can offer more sensitive braking close to the limit, because tiny changes in pedal pressure don't make huge differences in brake system pressure.

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. Any braking power or mechanical advantage in excess of this amount changes only how the lever feels and how hard you must squeeze it to get the braking you want, and cannot increase momentary braking force or power (which are limited by the bike's weight, wheelbase, tire traction, and weight distribution). Instrumented tests by BIKE magazine of Germany, as well as field results from tandemists, demonstrate that hydraulic discs fail at sustained power levels similar to mechanical discs and lower than that of rim brakes on sturdy rims.

That is why hydraulic brakes of whatever quality are not of any practical benefit with regard to gross stopping power. Good rim brakes and mechanical discs already have all the power it is physically possible to use, if you have normal grip strength. That's why I regard hydraulics as a waste of money, reliability, and user & field serviceability in most cases. To my mind, hydraulics are for people with very weak hands, or for bikes like front loading cargo bikes that have long, circuitous brake line routing. Beyond that, you are not paying for better braking performance-- you are paying only for the lever to feel different. You are accepting a brake that can't be repaired on the road or trail, for the sole benefit of its lever feel.
 
Here are some of my observations about brakes as used on electric bicycle:

E-bikes require more braking force in direct proportion to their increase in total weight (including rider) over pedal-only bikes. They require gross momentary braking power in proportion to the square of their speed. So in the e-bike application, a brake's ability to apply great force is secondary to its ability to absorb and shed lots of energy as heat.

Momentary braking force is a function of rotor radius, brake surface friction coefficient, and pad application force.

Maximum sustained braking power is a function of brake surface area, rotor mass and specific heat, thermal conductivity of the brake surface, temperature gradient to ambient, airflow over the hot components, and the components' tolerance of high temperatures.

Rotor size, mass, and thermal qualities are the only factors that figure into both braking force and maximum braking power. Brake rotors range in size from as small as 1-1/2 inches diameter inside the drum of a coaster brake hub, to about 25 inches diameter for a 700c wheel rim. Disc rotors currently available range in diameter from 5-1/2 inches to 8 inches, and today's drum brake diameters range from 2-3/4 inches to 3-1/2 inches. Larger discs and drums were available in the past.

It can be assumed that rim brake pad materials are the same in principle across all rim brakes, and disc brake pad materials are the same in principle among all bicycle disc brakes. Because the braking surface material and the application forces are very different between rim brakes and disc brakes, the two different kinds of pads are categorically different in nature. Rim brake pads are all some variation of rubber, while disc brake pads are harder fiber, ceramic, or metal-based composite materials. Drum brake shoe materials are equivalent to disc brake pad materials. Coaster brakes and roller brakes use metal-to-metal friction with grease lubrication.

How hard the pad is forced upon the rotor in any case is a matter of how hard the lever is pulled, the total mechanical advantage of the system, and the friction present in the system. The highest mechanical advantage is in coaster brakes, where perhaps an inch of backwards rotation at the pedal translates into a few thousandths of an inch in pad movement. (The high application force compensates for the brake's tiny rotor radius and low friction coefficient.) The lowest mechanical advantage is in long reach caliper brakes like those used on cruisers and older BMX bikes. Some of those that have short brake levers approach a 1:1 ratio of lever movement to pad movement.

Disc brakes are almost as high in their mechanical advantage as coaster brakes, where 20-30mm of lever throw might translate into about a millimeter of pad movement. Good rim brakes tend to have about 4:1 total mechanical advantage, with the upper end of the range approximately 10:1. Thus rim brakes must have much higher friction coefficients than disc brakes if they are to deliver similar braking force, which is why they use grippy rubber instead of hard ceramics in their pads. Disc and drum brakes can't use rubber pads, because the high application force would use up the pad's whole travel distance in squishing the relatively soft pad material before reaching full force.

Cable-actuated brakes have easily interchangeable levers, so it is possible to make significant changes in total mechanical advantage by switching to different levers with shorter or longer blades or different pivot-to-cable dimensions, or by using levers with adjustable leverage ratio such as Avid Speed Dial. The leverage ratios built into hydraulic brakes are fixed by the proportion between the master cylinder's area and the total area of all the slave cylinders connected to it. It is sometimes possible to switch to a master cylinder with a different diameter (if their hoses and hydraulic fluids are compatible), but it is a mechanical procedure much more tedious, complicated, and expensive than switching to a different cable lever.

Since ability to absorb and shed heat is the decisive factor in how suitable brakes are for fast e-bikes, it's worthwhile to understand how the differences in pads and rotors affect that ability. In disc brakes' favor, their pads can tolerate higher temperatures and are less damaged by reaching their thermal limits-- usually the friction coefficient temporarily drops (causing fade), and then returns as the pad cools. Disc pads must get smoldering hot before they melt or ablate away. Disc rotors can get much hotter than wheel rims, which increases their thermal transfer rate per area to the ambient air.

All the other parameters tend to favor rim brakes. Bicycle rims are much heavier than disc rotors, they are made of materials with much higher thermal capacity and conductivity, and they have much more surface area and more air flow over their surfaces. So at the limits of power disspation, good quality rim brakes on sturdy rims will always outlast bicycle disc brakes before the brake pads melt or burn, or the disc brakes fail by melting caliper parts or boiling their hydraulic fluid.

Throw in extraneous factors like poor quality pads, weak brakes that can't provide the desired braking force, draggy corroded cables, poor brake line routing, or other impairments, and a particular disc brake can easily outperform a particular rim brake. But that's not a reflection of the intrinsic potential of discs versus rim brakes, because the potential sustained power of rim brakes is always higher given today's generally available components.
 
Chalo said:
litespeed said:
I have Hayes Stroker on my 50+ mph Giant DH Team and personally could not imagine anything but a big 4 piston hydraulic caliper with a minimum of a 203 mm rotor to slow me down from those speeds.

Multi-piston hydraulic brakes on bicycles are a tribute to motorcycles rather than any kind of important or beneficial feature. As you point out, hydraulic brakes with especially strong lever response must be used carefully and can cause crashes. What they can't do is make you stop in a shorter distance than properly working rim or mechanical disc brakes. It's just like power brakes versus non-power brakes in a car-- they just make the pedal easier to push; they don't necessarily mean stopping distance will be shorter. In fact, the unpowered brake can offer more sensitive braking close to the limit, because tiny changes in pedal pressure don't make huge differences in brake system pressure.

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. Any braking power or mechanical advantage in excess of this amount changes only how the lever feels and how hard you must squeeze it to get the braking you want, and cannot increase momentary braking force or power (which are limited by the bike's weight, wheelbase, tire traction, and weight distribution). Instrumented tests by BIKE magazine of Germany, as well as field results from tandemists, demonstrate that hydraulic discs fail at sustained power levels similar to mechanical discs and lower than that of rim brakes on sturdy rims.

That is why hydraulic brakes of whatever quality are not of any practical benefit with regard to gross stopping power. Good rim brakes and mechanical discs already have all the power it is physically possible to use, if you have normal grip strength. That's why I regard hydraulics as a waste of money, reliability, and user & field serviceability in most cases. To my mind, hydraulics are for people with very weak hands, or for bikes like front loading cargo bikes that have long, circuitous brake line routing. Beyond that, you are not paying for better braking performance-- you are paying only for the lever to feel different. You are accepting a brake that can't be repaired on the road or trail, for the sole benefit of its lever feel.

We are just going to have to agree to disagree. I believe your a bit near sighted as to jot see the obvious differences but to each their own. As far as fixing them in the field goes it just plain silly. What a hose might break but a cable never would? Wet rim but all is ok?

I'll stick to my weak grip strength and wasted money.

Tom
 
litespeed said:
As far as fixing them in the field goes it just plain silly. What a hose might break but a cable never would?

If you have a 5mm allen key and a pliers with you, you can make your cable brake work again if the cable breaks at the caliper end. You might even be able to tie it back on if the end button breaks off. Good luck with a leaky hydraulic system. Do you have a crimper, some ferrules, and a bleed kit handy?

Wet rim but all is ok?

Discs get wet too. They stay wet, affecting their braking power, until the pads wipe them off. That's just the same as rim brakes. Drum and coaster brakes do stay out of rain and spray, but people seem to have magical notions that discs don't get wet or that their braking somehow isn't affected by water. I know from experience that my discs get weaker and make noise when they are wet.
 
That is a joke Chalo. Go speed down a wet mountain trail with your rim brakes, then try it again with good disc brakes. Then we'll talk about it.

Rim brakes are sh*t in a mountain, they are sh*t in the snow, and they aren't made at all for an 80 Lbs bike riding 80 Kmh all year long. They are made like motorcycle brakes, because riding a heavy bike down a mountain (or powered 10+ Kw) is very much like riding a motorcycle.
 
MadRhino said:
That is a joke Chalo. Go speed down a wet mountain trail with your rim brakes, then try it again with good disc brakes. Then we'll talk about it.

Rim brakes are sh*t in a mountain, they are sh*t in the snow, and they aren't made at all for an 80 Lbs bike riding 80 Kmh all year long. They are made like motorcycle brakes, because riding a heavy bike down a mountain (or powered 10+ Kw) is very much like riding a motorcycle.

I have barely ridden at all in snow, so I can't speak to that. If I wanted to ride in snow or ice, I'd use drum brakes and studded tires.

You ignore the fact that I own both discs and rim brakes, and that in the past I have also owned hydraulic brakes. I bought my first hydraulic brakes and my first discs more than 20 years ago. Furthermore, I owned three different heavy motorcycles equipped with triple disc brakes, and I have serviced many thousands of bicycle brakes of all types in the course of my work and pleasure. As a machinist, I made bicycle brakes and brake parts from scratch. And I have ridden e-bikes up to gross weights of more than 225 kg, and pedal trikes at gross weights up to 1450 kg. Right now, the pedal bikes I use for transportation weigh between 14 and 23 kg, and I weigh 145 kg at 2.03m tall the last time I checked. I have a special understanding of bicycle brakes, because I have been forced to develop this understanding if I want to ride safely.

I'm telling you, because I know it from direct experience, that a linear pull brake with a booster arch and Kool Stop Salmon pads is no more debilitated by wetness than a modern large rotor disc brake, and it's noticeably stronger than the disc when dry. On the other hand, my 229mm aluminum rotor full-floating cable-hydraulic bicycle disc brake was quite a bit more compromised by wetness than a good rim brake.

I am not speaking from ignorance, like those here who would compare a $200 hydraulic disc to a poorly maintained $10 rim brake and then pronounce all discs to be superior.

P.S. - "Wet mountain trails" don't allow nearly as much tire traction as clean wet pavement, so there is less braking available for that reason, and the type of brake becomes even less relevant.
 
Here's a fun observation. On my folding bike, I have a cable actuated cantilever brake up front and hydraulic rim brakes for the back. I ride year round, days as cold as 10 degrees fahrenheit. I store the bike inside, so when I go out on a very cold day the brake fluid actually starts to contract during my commute. I can feel the throw of my rear brake getting longer and longer as I near my destination - not buy much, but definitely noticeable. I even adjust it real quick at the lever when stopped at a red light. The cable brake is not similarly impacted by the cold.
 
Austin is still pretty close to western desert, so I don't doubt the right pads on rim brakes are quite adequate for Austin riders. They get wet days, bet this week was wet! But mostly not wet every day. Any good rider knows how to dry rims or disks when a stop sign is coming up. Or keep em dry on a hill descent.

Cheap mechanical disks, such as I have on some of my bikes are not a huge improvement over rim v brakes with cheap but new bell pads. But they do seem to give me a better fine touch on the brakes when riding trails. If used much, the cheap mechanical disk brakes fade like crazy.

Till I fork out the dough, and go to the big mountains and ride big, I won't comment about high end disk brakes. You have to ride them like an x games rider to judge it, and likely I'd ride it like an ex extreme sports dude at my age. I'd be creeping down it like the fraidy old fart I've become.

It's exactly the same as when I skied. Guys would say their old skis were fine. We'd chuckle and say, "fine for how and where you ski". Come to the double blacks and we'll watch those skis fail and laugh at you. To ski at that level, we had to have the best ski, not worn out, and keep it sharp enough to shave with. No different with brakes on a bike. At the bleeding edge, those who do it know what works and what makes them crash.
 
I think Shimano also deserves to be in the list of popular brakes ;)

yes they make crap but that only counts for the cheap stuff, pay a little more for LX brakes or better and you have something that will last!

I used:

hope M4: looks good, feels like a spunge, performance is crap, pads don't last long
hope M6: looks good, works good, very rare brake, brakepads seem to last forever
my opinion about hope brakes: waste of money, looks good (I even used their floating disks for downhill mountainbiking and I broke them, they refused to replace them under warranty)

Avid juicy 5: good performer, easy to maintain, reservoir leaks sometimes and it even sprayed oil into my eyes once
good value for money ;)

Formula disk brakes: overall a real pain to bleed, don't like rough weather and salty roads, once they start to act weird => trash them (the local LBS even sends them up for bleeding / repair) medium performance
doesn't last long for daily use

shimano cheap ass mechanical disk brakes => rubbish, low brake power, go for V brakes instead if you are on a budget ;)

Shimano SLX disk brakes: very adjustable, a pleasure to bleed / clean / work with, impressive power

Shimano Saint: NOTHING BEATS IT! nothing bad to say about it, extremely powerfull and adjustable!
will flip your bike during a panic front brake!!!!!


the best disks: (my opinion)
AVID G2 clean sweep!
 
dogman said:
Till I fork out the dough, and go to the big mountains and ride big, I won't comment about high end disk brakes. You have to ride them like an x games rider to judge it, and likely I'd ride it like an ex extreme sports dude at my age. I'd be creeping down it like the fraidy old fart I've become.

But you do understand that a foolhardy youngster on a loose surface can only exert a tiny fraction of the braking torque that a fat guy on flat pavement can, right? Or a tandem team? Or a loaded longtail rider? It doesn't matter how "extreme" the trail is. There are always the physics of the bike and the physics of the surface to set an upper limit on braking.

Riding fast down a steep unpaved trail is actually a very poor measure of braking power, because applying more than a little bit of braking will either chuck you off or cause you to slide out. That might be a nice time to have "one finger" brakes-- just so you have the other fingers available to hold on with-- but it's no test of braking power at all.
 
spinningmagnets said:
Thanks, 3nslav3. All the posts here are useful to me, but that is the type of comparative info that is the most valuable.

Then here's another nugget for you: No Promax disc brake I have ever come across is more effective than dragging your foot on the tire. Don't even bother.

EDIT:
To be honest, it's not always useful to make anecdotal comparisons of specific brake models, because most brakes are sensitive to changes in friction materials and setup. Some brakes are terrible with the stock pads but work great with upgraded ones. Some brakes, like cantilevers, work well if you know how to set them up just so, but they hardly ever get set up just so. If your brake isn't hydraulic, then it doesn't have a dedicated lever, and levers can make a huge difference in how the brake performs and feels.

I don't think it's quite fair to any rim brake to assess its effectiveness without using Kool Stop pads, for instance. Likewise, you don't know what a given disc brake can do if you don't try a good sintered metal pad (which isn't always an option because of proprietary disc pads).
 
Here is a little something that worked for me. I ride a tadpole trike and it came with BB7's and 160mm rotors. It was very sensitive to lock up and could stand me on my nose easily. I replaced the 160 with 185 rotors and my ability to modulate the brakes really improved. It was good enuff thatI decided not to go to 200's. That extra radius makes the brakes more powerful yet seems to help modulate. I dunno but it worked for me.
otherDoc
 
I will add a few comments for consideration...
If you look at the design of the caliper,cantilever , and "V" brakes, you will notice that the "V" brake has a much greater (+50%) mechanical advantage ( distance between the pivot to the pad, and the pivot to the cable attachment ), hence for any particular cable force the "V" brake will exert a greater force to the pads...hence why they are the most effective rim brake.

As Chalo mentioned , there are specific levers that MUST be used with "V" brakes. Dito, for other styles also.

Pads ,..correct choice of, is probably more important than the type of brake you have.

Disc brakes are excellent, but always remember they transmit all the braking force through the spokes, an additional and much higher loading than most spokes were intended for. This may not be a problem for those that regularly true and tension their wheels, but for the "fit and forget" users....dont be surprised if you have issues with loose/broken spokes, or wheels going out of true.

One of the advantages of a "bicycle" is its simplicity and relative low maintenance, and repairs that can be done with simple tools on the roadside. and to that end i prefer to use simple equipment on my bikes. that means no place for hydraulics. ( and in practice ..no need for them either )

If your brake can lock the wheel, or tip you over the front, it is more than sufficient. You should be riding in a manner where you dont rely on brakes to save your neck. :wink:
 
Hillhater said:
Disc brakes are excellent, but always remember they transmit all the braking force through the spokes, an additional and much higher loading than most spokes were intended for.
How much higher? :? A ball park figure will do.


Hillhater said:
One of the advantages of a "bicycle" is its simplicity and relative low maintenance, and repairs that can be done with simple tools on the roadside. and to that end i prefer to use simple equipment on my bikes. that means no place for hydraulics.
Simplicity and low maintenance? Hydraulic disks will win on both. At least in my case.
The Avid Juicy I purchased in Oct 2009 from CRC were ~ $100 a pair. So far I have replaced pads 3~4 times and other than that have done no maintenance whatsoever. That's ~40,000km of use, rain hail or shine.
In similar conditions a rim brake system would need constant adjustments as the pads wear, a couple of cable changes and possibly a rim swap. :lol:


Have you even tried discs??
 
spinningmagnets said:
...Disc brakes...transmit all the braking force through the spokes...

I never thought about this before, thanks for that info.

For a wheel in good repair, the change in spoke tension when hub braking isn't very much. A front wheel can brake with a force equal to maybe, maybe 70-75% of the gross weight of the bike. So for a 300 pound bike + rider + luggage combination, you're looking at an absolute maximum of a little over 200 pounds tangential force at the contact patch before you get catapulted. In practice, it isn't even that much. But coincidentally, 200 pounds is approximately the static tension of a single spoke in a lightweight bicycle wheel.

In a 36 spoke wheel that's consistently and uniformly tensioned, that 200 pound tangential load would be divided evenly among 18 spokes that get tighter and 18 spokes that get looser. None of them will have a problem with that; the bike's weight, which is borne by about four spokes at a time in each wheel, causes much larger tension excursions. The problems arise when there are broken spokes, loose spokes, or spokes that are overtightened to near their yield strength (or the rim's). When that happens, the spokes don't share loads uniformly around the wheel and things can deteriorate quickly.
 
Chalo said:
.... that 200 pound tangential load would be divided evenly among 18 spokes that get tighter and 18 spokes that get looser..

Now here is an interesting calculation for someone attracted to force vector resolution...
assuming that 200lb (f) tangential braking load is reasonable, what load is transmitted to each of the 18 loaded spokes , considering that they are attached near perpendicular ( 5-10 deg ?) to the rim ..( and direction of the braking load )?
 
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