Disk or V brake, pros and cons.

[Mussels]

I see some people denouncing disk brakes whilst others say they would never go back to rim brakes, but few really explain why. Of the dubious new technoligies I've seen on pushbikes this seems like one of the stayers. I'd expect the fashion conscious rider to shun them as they are heavier than rim brakes but they are regarded as a fashion item by traditionalists*.
In theory everyone should hate them so why are they so popular and could they actually be better than rim brakes?

* I know there wont be many conservative riders on a pedelec forum but the brake issue is still like marmite on here.

 

[Lloyd_50cycles]

Hi Mussels,
Disc brakes are more popular for mountain bikes, and v-brakes for most others. Just to confuse matters bmx use U-brakes, road bikes (the lycra gang as they are affectionately referred to on this forum) use caliper brakes and cyclo cross use cantilevers. V brakes are a type of cantilever. Now for anyone who is still awake I will explain why....

Each brake offers a certain advantage to certain styles of cycling. Disc brakes(hydraulic) are super powerful, but offer an advantage to mountain bikes mainly as they don't clog in the mud and work in all weather conditions. Now the disadvantages are the extra weight(though there are super light carbon versions available), and maintainence. Neither of which the mountain bikers are usually all to bothered about.

Road bikes use calipers for weight alone, they are the lightest brakes available,and lets face it proper roadies(lycras) don't actually brake.Ever.So the poor performance doesn't matter as much as weight. Plus they never get muddy.

Cyclo cross bikes use cantilevers as thats in the rules of the sport. That is the main reason to be honest.

BMX bikes use U brakes as they allow reasonable braking performance, but the main point is they allow the handlebars to be rotated 360 degrees for tricks. Again no mud in BMX, weight isnt a problem so thiese are the ideal brakes.

Now V brakes are for everything else. This is because they work very well, are easy to maintain, very simple and light. To be honest they are perfect for most E bikes used for general use and commuting.

In my opinion hydraulic disc brakes are better in performance, but V brakes perform well enough for most E-bikers and are light and easy to maintain. This is why they are very popular. Hydraulic discs are a bit overkill to be honest, if you are hurtling down the Alpes off road through the mud on your E-bike you should probably look at a new bike.

There are a couple of other things to consider. There are disc brakes that aren't hydraulic. These are a waste of space, as they are really for looks only. They offer no extra power. In fact a well set-up set of V brakes will out perform a cable operated disc! Also hydraulic discs can become contaminated easily, so extra care must be taken when cleaning and lubricating etc.

 

[flecc]

As I've remarked elsewhere, the primary determinant of braking efficiency is disc diameter, and since the wheel rim is the largest possible disc, rim brakes (caliper or V) are superior if all other things are equal.

Just have a look at the world of cars. The faster the car the larger the disc.

There's also the spokes factor. Disc brakes have to exert all the braking force via the spokes, where rim brakes are directly transmitting the braking effort into the rim, tyre and road. That again makes the rim brake potentially superior.

And in road racing, only rim brakes are used since among other reasons that Lloyd has given, on long fast descents disc brakes suffer from heat build up which can buckle discs and damage hubs. Tour de France riders can brake from 65 mph at times.

Of course the fashionistas will disagree with all this and continue to think style means efficiency.
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[Bigbee]

Good points.

Trouble is people( like me) would look at a bike with discs in preference to one with V's.,and assume the brakes are superior.Now maybe I wont

 

[flecc]

Good points.

Trouble is people( like me) would look at a bike with discs in preference to one with V's.,and assume the brakes are superior.Now maybe I wont

In fairness Bigbee, it probably scarcely matters for most users what type of brakes they use since few use the brakes to extreme extents, so the smart appearance of discs can be preferred with a clear concience.

Probably a more practical objection for many is the frailty of discs. The steel discs commonly used on bikes are very thin for weight saving reasons and the centre is supported on arms rather than being solid, since solid transmits heat into the hub bearings too efficiently.

All this means discs are easily damaged and a buckled disc often leaves a bike unwheelable which could be highly inconvenient. That's not uncommon and we've had th odd buckled disc reported in here, but I cannot recall ever seeing V brake arms buckled.

I'm also not happy with discs on hub motors since they can already get too hot for comfort in hot weather and the added braking heat bolted on then becomes undesirable.
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[frank9755]

I think Lloyd sums it up pretty well!

A couple of other points:

- Sheldon Brown, who knew as much about bikes as anyone ever will, said that disc brakes were fine with suspension forks but felt 'funny' with normal forks, so didn't recommend them for on-road bikes

- If you want to add an element of excitement to your braking you can always combine disk brakes with quick release. This gives you a kind of cycling Russian roulette, as there is always a chance that a quick release will work loose. If it is loose and you brake hard, and your droppouts point the normal way, there is a chance that your fork will get thrown clear of your wheel by the braking action, and you will have a short period of flying followed by a nasty bump! Apparently it does happen occasionally. For that reason most bike manufacturers don't combine them - however the Ezee Torq Trekking does!

 

[Teejay]

An objection to Rim Brakes is - they wear out the Rims! As they are already carrying the tyre and, indirectly, you, so a vital component under quite a bit of stress - I ask is this really sensible engineering?

 

[flecc]

And not only with quick release and there have been many warnings about the event Frank refers to.

The problem is one of fundamental bad design from the beginning of disc brakes on front bicycle wheels. The caliper to disc geometry is such that braking force tries to propel the wheel downwards and out of the forks. Having the caliper and pads well forward of the forks removes the problem, but most have the caliper at the rear of the forks and have the potential for wheel ejection.

Still, I must say something nice about discs, so they do save rim wear.
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[flecc]

An objection to Rim Brakes is - they wear out the Rims! As they are already carrying the tyre and, indirectly, you, so a vital component under quite a bit of stress - I ask is this really sensible engineering?

My post above including rim wear crossed with yours.

The answer to your question is both yes and no! Viewed purely as an engineering matter as you have, it does seem to be bad practice, but as I've noted above, transmitting the braking force via the spokes as disc brakes do is also very bad engineering practice. And as I've also noted, braking directly into the rim and therefore the tyre and road is good practice in braking efficiency terms.

However, many things on bikes are superficially bad practice since there are overriding factors like weight and avoidance of added complexity. The essence of a good bicycle is simplicity and minimalism, and this means that it's desirable for parts to perform more than one function wherever possible. Using the existing large disc of the rim for braking makes perfect sense in bicycle design terms, and there are many safety factors included to prevent rim failure being a problem. Double thin walls are one, wear indicator grooves another, modern pad formulation yet another, and even ceramic coatings on rims in some cases.

Most of the horror stories about rim failures are very old, dating from the adoption of alloy rims after steel rims had been the norm for most of the bicycles existence. Then the early alloy rims were metallurgically inferior, the pads were hard, harsh and very unsuitable, and the brakes themselves were inferior in design, so failures became a problem at that time.
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[tillson]

Sorry to move this thread slightly away from the original topic, but this is brake related.

The brake blocks on my Pro Connect are starting to get a bit thin. (V Brakes) Will any blocks suitable for V brakes be OK as replacements? Or do they have to be Shimano?

I see there are many different sorts on SJS Cycles website. Any recommendations?

Thanks

Tom

 

[flecc]

I generally use Shimano replacements but have been happy with the Avid 20R type and have even successfully used the cheap Birmingham made Clarks MTB pads from Halfords.
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[Lloyd_50cycles]

V brakes use 3 types of pad. Threaded, non-threaded and cartridge. The Pro Connect uses cartridge pads, the Agattu threaded pads. I have attatched some images but they are a bit small. The main difference is the cartridge pads just slot out, and are secured by a pin. The threaded ones are attatched with a threaded barrel on the actual pad, and non threaded ones are attatched via a stalk that sticks out the pad and isnt threaded. The most common ones are Threaded. Shimano ones are good, but Aztec offer a budget alternative that are excellent.

 

[Footie]

I see some people denouncing disk brakes whilst others say they would never go back to rim brakes, but few really explain why. Of the dubious new technoligies I've seen on pushbikes this seems like one of the stayers. I'd expect the fashion conscious rider to shun them as they are heavier than rim brakes but they are regarded as a fashion item by traditionalists*.
In theory everyone should hate them so why are they so popular and could they actually be better than rim brakes?

Before I got my electric bike I had always had rim brakes.
My MTB electric bike came with disk brakes.
From my own experience - they are a bitch to get set up right and need constant adjustment. They continually rub, dragging the bike speed down to a crawl.
If I could change anything on my ebike it would be to bin the disk brakes and put rims on it.

You ask are disk brakes better than rim brakes?
Not as far as I am concerned - load of c**p
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[wibble]

From my experience - hydraulic disk brakes are far superior to cable brakes.

Cable based disk brakes are a manufacturer's way of making a bike look like the more costly hydraulic braked bikes. They're no better than rim based brakes.

 

[wibble]

Before I got my electric bike I had always had rim brakes.
My MTB electric bike came with disk brakes.
From my own experience - they are a bitch to get set up right and need constant adjustment. They continually rub, dragging the bike speed down to a crawl.
If I could change anything on my ebike it would be to bin the disk brakes and put rims on it.

You ask are disk brakes better than rim brakes?
Not as far as I am concerned - load of c**p
.

I totally agree!

 

[Tiberius]

I agree that rim brakes make the most sense from the engineering p.o.v. I did, though, get some rim damage from them once. The bike came with some cheap and nasty brake blocks and the metal mountings were only a little depth below the rubber surface. It didn't take much use to get metal to metal contact.

Has anyone tried using dual rim brakes? I can see two ways this could be done, one by just doubling up, or a second way in which a long brake block spans across two sets of levers. That second way would ensure correct alignment.

Nick

 

[flecc]

I agree that rim brakes make the most sense from the engineering p.o.v. I did, though, get some rim damage from them once. The bike came with some cheap and nasty brake blocks and the metal mountings were only a little depth below the rubber surface. It didn't take much use to get metal to metal contact.

Has anyone tried using dual rim brakes? I can see two ways this could be done, one by just doubling up, or a second way in which a long brake block spans across two sets of levers. That second way would ensure correct alignment.

Nick

Yes, the pad type and quality does need to be right to avoid wear.

I've never tried dual brakes but always use long pads, changing to them immediately when the originals are short. Your second way for dual does sound attractive.

Bicycle law has created some one-off dual brakes though. Bikes have to have two brakes by law but they can both be on the same wheel (!), so many have solved brake mounting problems on other wheels by this device. Manufacturers also often make trikes this way, but usually with a combination of hub and rim brake on the front wheel.
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[Mussels]

Before I got my electric bike I had always had rim brakes.
My MTB electric bike came with disk brakes.
From my own experience - they are a bitch to get set up right and need constant adjustment. They continually rub, dragging the bike speed down to a crawl.
If I could change anything on my ebike it would be to bin the disk brakes and put rims on it.

You ask are disk brakes better than rim brakes?
Not as far as I am concerned - load of c**p
.

A few people reported similar problems with the disk brake on the Wisper but I found that after putting a good quality cable on then the brakes were much easier to set up and go a few hundred miles between adjustments.
I don't agree with flecc about larger rims having better braking efficiency, they are bigger in cars to deal with the greater heat caused by increased braking. The same benefit is not so obvious on a pushbike as the disk can withstand higher temperatures than the rim and a hot disk disperses heat much better than a warm rim so could deal better with prolonged braking.
Cable disk brakes may have less absolute stopping power than rim brakes but I find the disk brake has better feel, is more consistant in all conditions and requires less maintenance than the rim brakes - the rims require frequent cleaning but the disk looks after itself pretty much.
I've not see any complaints on the net about broken disks but I have seen plenty about worn out rims due to the drive for constant weight reduction, in particular Shimano pads are blamed for excessive wear. I'd rather replace a disk every year than a rim every 2 years.
Coincidentally I bumped into an obsessive cyclist (likes to do the Alpine TDF routes for a holiday) last night who said he would love to fit hydraulic discs to his road bike but the rules don't allow it, I asked him why as I thought the extra weight would make them unpopular and he told me the performance benefits far outweigh the weight cost.
I prefer the feel of the disk brake now it is set up properly but I want to keep an open mind, I think that as soon as racing rules catch up and allow disk brakes then their development will accelerate and will become the prevalent technology.

 

[flecc]

I don't agree with flecc about larger rims having better braking efficiency, they are bigger in cars to deal with the greater heat caused by increased braking. The same benefit is not so obvious on a pushbike as the disk can withstand higher temperatures than the rim and a hot disk disperses heat much better than a warm rim so could deal better with prolonged braking.

Absolutely not so. Heat dispersal is not a problem on road car discs due to the substantial nature of the mounting forming a large heat sink in addition to the cooling air, something bikes don't have. If heat were a problem the discs would not be made solid but would be perforated and arms mounted like bike discs.

The larger the disc diameter, the higher the linear speed and the greater the pad friction at a given pressure so resulting in the greater efficiency since friction is the braking force. It's irrefutable physical law.

The rim is only warm as you say precisely because it's greater volume and area is much better at dispersing the heat for a given braking force than a small disc. In fact heat in rims is a negligible problem on road bikes, but can be a real problem in discs and the buckled ones are sometimes evidence of that.
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[Lloyd_50cycles]

I'm going to jump on the physics boat aswell now ....he he. Its down to leverage. Rim brakes bite at the end of the wheel, so have more stopping power in that sense, discs bite at the centre of the rim, so have less. This is evident because 203mm discs used in downhill mountain biking are far more powerfull than 165mm diameter discs used in cross country races. Now thats if the forces of braking are equal. So cable disc versus a decent, well set up(thats the key words here) V brake.....V brake wins. Hydraulic disc brake versus the same well set up v brake, the hydraulic disc brake with its 1100 psi of pressure wins(it has much more power). But get a magura hs11 hydraulic rim brake, versus a hydraulic disc brake, rim brake wins. This is proven as it is the brake of choice for trials riders, who need the most powerfull and sensitive brakes of all. There will be people who have only ever had poor quality cable discs who will tar all discs with the same brush, the same goes for v brakes. There are nasty cheapo V brakes that feel like sponges, with rim eating pads. You need to make sure that whatever brakes you do have, they are set up well, and are good quality. And as for discs on road bikes, another reason they wont be on them for a while is that the sheer force they excert would mean they would probably rip the disc mounts off the frames on long alpine descents.......scary thought. Unless you beefed up the frame mounts, tubing profile, spokes(aero blade radials would rip themselves apart), forks, oh heck just buy a mountain bike......he he.