Disc brakes pros and cons

norvernrob

thegreatdivide wrote:

NorvernRob wrote:

(including other really crap ones with broken surfaces and loose gravel where I had to brake pretty much constantly)

Col de l'Arpettaz?

Yes it was, top marks! The surface going up it was bad enough, my wheels slid several times in the gravel that looked like a little bit of top dressing but was actually a couple of inches deep. I descended down the other side but wasn’t willing to take any risks as it was a similar surface.

norvernrob

Stueys wrote:

Always chuckle at everyone arguing why they don’t need better braking performance. I’ve yet to brake from 40+ mph thinking I needed a bit less braking capability....

True, but my thoughts are that the combination of rim brakes/pads/wheels on my Foil are so good that there is absolutely no need to change them. They’re not going to get any more of a test than they’ve just had and I was 100% happy, in fact I’m off to the Alps again in a week’s time and won’t be changing a single thing on the bike.

Discs are great, but in my own opinion and experiences th advantages don’t lie in outright braking power in normal circumstances, but in dirty, wet rides, commuting, big miles, off road riding etc. All of which I do on my CX bike and hence I have discs on it.

veronese68

NorvernRob wrote:

True, but my thoughts are that the combination of rim brakes/pads/wheels on my Foil are so good that there is absolutely no need to change them. They’re not going to get any more of a test than they’ve just had and I was 100% happy, in fact I’m off to the Alps again in a week’s time and won’t be changing a single thing on the bike.

Discs are great, but in my own opinion and experiences th advantages don’t lie in outright braking power in normal circumstances, but in dirty, wet rides, commuting, big miles, off road riding etc. All of which I do on my CX bike and hence I have discs on it.

That all makes sense, I don’t know how heavy you are or if there is a weight at which discs would be more advantageous when coming down a mountain. But certainly for the latter reasons I will stick with discs. Riding across South London in the rain last night I was very glad to have confidence in my braking that I wouldn’t have had on the rim braked bikes I’ve had. Yes, the brakes honked a bit. But it did save me yelling at the daft bint that stepped out without looking. So even the cons have an upside.

thegreatdivide

NorvernRob wrote:

thegreatdivide wrote:

NorvernRob wrote:

(including other really crap ones with broken surfaces and loose gravel where I had to brake pretty much constantly)

Col de l'Arpettaz?

Yes it was, top marks! The surface going up it was bad enough, my wheels slid several times in the gravel that looked like a little bit of top dressing but was actually a couple of inches deep. I descended down the other side but wasn’t willing to take any risks as it was a similar surface.

Annecy area + gravel hell - it could only be one climb ;-)

It makes the Glieres look like a blackboard.

norvernrob

Veronese68 wrote:

NorvernRob wrote:

True, but my thoughts are that the combination of rim brakes/pads/wheels on my Foil are so good that there is absolutely no need to change them. They’re not going to get any more of a test than they’ve just had and I was 100% happy, in fact I’m off to the Alps again in a week’s time and won’t be changing a single thing on the bike.

Discs are great, but in my own opinion and experiences th advantages don’t lie in outright braking power in normal circumstances, but in dirty, wet rides, commuting, big miles, off road riding etc. All of which I do on my CX bike and hence I have discs on it.

That all makes sense, I don’t know how heavy you are or if there is a weight at which discs would be more advantageous when coming down a mountain. But certainly for the latter reasons I will stick with discs. Riding across South London in the rain last night I was very glad to have confidence in my braking that I wouldn’t have had on the rim braked bikes I’ve had. Yes, the brakes honked a bit. But it did save me yelling at the daft bint that stepped out without looking. So even the cons have an upside.

Weight is a good point. Sat on my bike with full bottles and all my stuff the total weight is probably around 77-78kg (im 66kg). I might have a different view if I was trying to slow up 100kg+.

meanredspider

It’s a dull conclusion but disc brakes are good brakes and you only need them if you need good brakes.

apreading

What gets me is that you dont see the same people continually questioning Shimano 6800, saying that 5700 was enough and they dont need the better brakes or shifting, or any other step up in traditional rim brake systems - which people have complimented and embraced. But only when it somes to discs, suddenly they say that they dont want better brakes and dont see the point.

Despite what many naysayers insist, its not about the fact that disc brakes can brake harder, its more about that their full braking force is available instantly, rather than waiting for it to kick in, that it is easier to access, requiring little effort on the levers (particularly in the hoods where rim brakes sometimes harder to use), that it is more controllable and more precise, that it requires less maintenance, works in all weather equally well, allows for wider tyres with more grip and smoother ride, AND pretty much last on the list that it allows you to brake harder if and when you want/need - because there IS more grip that rim brakes let you easily access and there is even more grip still if you have wider tyres that you couldnt have with rim brakes.

I hated hydraulic disc brakes when I first got them on a mountain bike - they were a nightmare and I wondered why on earth people didnt all prefer V-brakes. So much that I made sure the kids bikes came with BB5/BB7 mechanical discs. Then I realised that my problem was just because I had Avid Juicy disc brakes - as soon as I got Elixirs and Shimano brakes I realised they were fantastic. I would have argued till I was blue in the face against them until I saw the light. Some people just havent had that lightbulb moment yet.

neeb

apreading wrote:

What gets me is that you dont see the same people continually questioning Shimano 6800, saying that 5700 was enough and they dont need the better brakes or shifting, or any other step up in traditional rim brake systems - which people have complimented and embraced. But only when it somes to discs, suddenly they say that they dont want better brakes and dont see the point.

That's because it's a bad comparison. One is an incremental improvement of an existing system (with no real disadvantages), the other is a completely different system, with both advantages and disadvantages.

apreading wrote:

its more about that their full braking force is available instantly, rather than waiting for it to kick in

Not sure what you are getting at unless you are talking about wet weather specifically - both systems are effectively instantaneous (you may need to pull a bit harder to get the same effect with rim brakes but you will almost always be modulating the brakes anyway and not applying full force in order to avoid lock ups / skids).

apreading wrote:

requiring little effort on the levers (particularly in the hoods where rim brakes sometimes harder to use),

The "effort" required to operate good rim brakes is minimal, unless maybe you are right on the limit on a 40-50mph descent on a 12% slope. Obviously it's directly proportional to total system weight though, so will be greater for heavier riders.

apreading wrote:

requires less maintenance,

It requires different maintenance, and if it requires major maintenenace (as it eventually will) it is much more hassle.

apreading wrote:

works in all weather equally well,

True, I'll concede that one.

apreading wrote:

allows for wider tyres with more grip and smoother ride,

How wide do you want your tyres to be?? Modern rim brake frames are mostly fine with 28mm, which is wider than I'd want to run on normal roads and the widest I'd ever want to run on a full-on road bike.

apreading

neeb wrote:

One is an incremental improvement of an existing system (with no real disadvantages), the other is a completely different system, with both advantages and disadvantages.

But its an improvement that disc brake bashers argue is pointless because they were already at the limit of tyre grip.

How wide do you want your tyres to be?? Modern rim brake frames are mostly fine with 28mm, which is wider than I'd want to run on normal roads and the widest I'd ever want to run on a full-on road bike.

Not if you want to run mudguards. Few rim brake bikes will run 28s with mudguards. Many, also struggle with 25s and mudguards.

neeb

apreading wrote:

neeb wrote:

One is an incremental improvement of an existing system (with no real disadvantages), the other is a completely different system, with both advantages and disadvantages.

But its an improvement that disc brake bashers argue is pointless because they were already at the limit of tyre grip.

That's not my argument against discs, I don't think they are pointless - they clearly offer better wet weather performance, especially on descents. But they have a whole set of little disadvantages that collectively outweight the advantages for a performance orientated road bike.

apreading wrote:

Not if you want to run mudguards. Few rim brake bikes will run 28s with mudguards. Many, also struggle with 25s and mudguards.

Yup, and I'd probably want discs on a road bike I planned to run mudguards on (if I ever buy a new winter bike it will doubtless have discs). That's not my best summer bike though..

Seems heretical to buy a complete new winter bike though, as opposed to using at least some hand-me-down bits - and there's another problem with discs, complete incompatibility with anything else made in the last 40 years..

meanredspider

The effort required for rim brakes needs to take into account all of the mechanical inefficiencies of the system:
- stretch in the cable
- flex in the outer
- flex and play in the caliper
- compression in the brake blocks
- compression of the rim
- friction in the entire system

Hydraulic disc brakes do away with nearly all of these. Fluids are low friction and incompressible. Disc pads are very low compression and the discs effectively incompressible. The caliper itself can be very stiff. All movements are very small.

Then you can select your braking surface materials to just do braking on a disc brake. On a rim brake it’s just a compromise. The rim of the wheel needs to be the rim of a wheel as well as a braking surface. The diameter is decided by the wheel not by any other choice.

Rim brakes are a compromise - and that’s fine if you don’t need great brakes. My Foil has rim brakes because I bought it for N Holland. You don’t need good brakes in N Holland. My Volagi has disc brakes because I bought it for the Highlands. You need good brakes in the Highlands.

neeb

meanredspider wrote:

Rim brakes are a compromise - and that’s fine if you don’t need great brakes.

Disc brakes are a compromise too - just with a different set of trade-offs.

And modern rim brakes ARE great brakes, they are perfectly suited to a particular application. A well-designed electric coffee-stirrer would doubtless be more efficient than a teaspoon, but for most coffee stirring applications is massively OTT with associated disadvantages. But if your job involved stirring 100 coffees as quickly as possible, or if you had two broken wrists, it might be a good investment.

I acknowledge that if you live in a part of the western highlands of Scotland where there’s more than 200 days in the year when it rains, discs are probably a good idea.. but that’s an extreme climate in a global or even a UK context.

thegreatdivide

neeb wrote:

Seems heretical to buy a complete new winter bike though, as opposed to using at least some hand-me-down bits - and there's another problem with discs, complete incompatibility with anything else made in the last 40 years..

I couldn't agree more. As I posted on another thread, the winter bike is where old parts go to die.

ugo.santalucia

Aside from the old "rim wear" argument, which is still valid... disc brakes are superior when it comes to stopping distance in the wet...

I tend to ride very conservatively in the wet, to avoid losing grip in a corner, so don't feel like disc brakes are needed there.
Some would argue: what about coming down the Galibier when it's wet? Well, you were a bit of a moron to go up the Galibier without checking the forecast in the first place, but if you are there, I would say that keeping warm is a more immediate issue than stopping distance...
You can manage with an increased stopping distance by riding carefully, which trumps good brakes when it comes to safety... always

londoncommuter

ppp

green_mark

neeb wrote:

apreading wrote:

Not if you want to run mudguards. Few rim brake bikes will run 28s with mudguards. Many, also struggle with 25s and mudguards.

Yup, and I'd probably want discs on a road bike I planned to run mudguards on (if I ever buy a new winter bike it will doubtless have discs). That's not my best summer bike though..

Seems heretical to buy a complete new winter bike though, as opposed to using at least some hand-me-down bits - and there's another problem with discs, complete incompatibility with anything else made in the last 40 years..

A rim brake bike that accepts 28mm will need longer the brake pads set further along the calipers than for a rim brake bike that accepts only 25mm. That does mean less brake leverage.

With discs you can get all the Pros from larger tyres without that loss in brake leverage: better braking both wet and dry, lower rolling resistance, better puncture resistance, better comfort. Those are all pluses that can be used in a summer bike.
Cons for wider tyres are weight and reduced stiffness due to needing to accommodate a wider chainline.

ayjaycee

green_mark wrote:

A rim brake bike that accepts 28mm will need longer the brake pads set further along the calipers than for a rim brake bike that accepts only 25mm. That does mean less brake leverage.

?????????????????????????? Expand please.

surfercyclist

I thought it had been pretty much proven that disc brakes stopped better, wet or dry? Much better in wet but slightly better(maybe) in dry. I have Ultegra rim brakes(Canyon bike spec was you get what you're given), however I think next bike will have discs. I live in a hilly area so having better brakes can only be a good thing. Yeah, maybe the pads cost a bit more but if it saves you a spell in hospital gotta be worth it...

imposter2.0

green_mark wrote:

A rim brake bike that accepts 28mm will need longer the brake pads set further along the calipers than for a rim brake bike that accepts only 25mm. That does mean less brake leverage.

V-brake pads are typically longer than standard caliper pads, but other than that, what you say here is simply not correct.

green_mark wrote:

Cons for wider tyres are weight and reduced stiffness due to needing to accommodate a wider chainline.

No idea what this means either. Can you elaborate?

frisbee

Imposter wrote:

green_mark wrote:

A rim brake bike that accepts 28mm will need longer the brake pads set further along the calipers than for a rim brake bike that accepts only 25mm. That does mean less brake leverage.

V-brake pads are typically longer than standard caliper pads, but other than that, what you say here is simply not correct.

green_mark wrote:

Cons for wider tyres are weight and reduced stiffness due to needing to accommodate a wider chainline.

No idea what this means either. Can you elaborate?

I think he means that a rim brake bike with clearance for 28mm tyres is likely to be using long reach callipers. Long reach callipers are generally a bit poo.

For the second point I'm guessing he is talking about 135 and 142mm rear dropout spacing.

imposter2.0

frisbee wrote:

I think he means that a rim brake bike with clearance for 28mm tyres is likely to be using long reach callipers. Long reach callipers are generally a bit poo.

For the second point I'm guessing he is talking about 135 and 142mm rear dropout spacing.

Well, if that's what he means (and well done for translating) then I'm still not sure it's correct. The newest caliper designs from Shimano will take 28mm tyres. As for the chainline thing - chainline is defined by the chainset/BB and is basically unaltered by dropout spacing in any case.

neeb

Imposter wrote:

frisbee wrote:

I think he means that a rim brake bike with clearance for 28mm tyres is likely to be using long reach callipers. Long reach callipers are generally a bit poo.

For the second point I'm guessing he is talking about 135 and 142mm rear dropout spacing.

Well, if that's what he means (and well done for translating) then I'm still not sure it's correct. The newest caliper designs from Shimano will take 28mm tyres. As for the chainline thing - chainline is defined by the chainset/BB and is basically unaltered by dropout spacing in any case.

I suppose what he means is that if the frame is designed to be able to take 28mm tyres then the distance between the frame fixing point of the brake and where the pads are set will be a little bit more than with a frame that has less clearance (with the same brakes you will need to fix the pads a little further towards the ends of the calipers). Good modern rim brakes will be designed to be stiff enough to cope with this though and any difference will probably hardly be detectable.

And it's true (I think?) that with wider dropouts and disc wheels the cassette will be shifted slightly outwards relative to the chainset (assuming q factor is the same), and so chain lines will more crossed at the extremes. That's why most disc frames have slightly longer chainstays (to counteract that), which potentially leads to less drivetrain stiffness.

apreading

neeb wrote:

And it's true (I think?) that with wider dropouts and disc wheels the cassette will be shifted slightly outwards relative to the chainset (assuming q factor is the same), and so chain lines will more crossed at the extremes. That's why most disc frames have slightly longer chainstays (to counteract that), which potentially leads to less drivetrain stiffness.

Its also countered by the BB386 on my bike - a wider bottom bracket with external bearings that fixes all the problems with press fit/BB30 while retaining the larger bearings and at the same time fixes the chainline with wider axles.

meanredspider

neeb wrote:

I suppose what he means is that if the frame is designed to be able to take 28mm tyres then the distance between the frame fixing point of the brake and where the pads are set will be a little bit more than with a frame that has less clearance (with the same brakes you will need to fix the pads a little further towards the ends of the calipers). Good modern rim brakes will be designed to be stiff enough to cope with this though and any difference will probably hardly be detectable.

And it's true (I think?) that with wider dropouts and disc wheels the cassette will be shifted slightly outwards relative to the chainset (assuming q factor is the same), and so chain lines will more crossed at the extremes. That's why most disc frames have slightly longer chainstays (to counteract that), which potentially leads to less drivetrain stiffness.

The longer the reach of the calipers, the lower the mechanical advantage.

And a disc cassette is the same as a rim cassette. The chain line will be exactly the same as the a rim brake bike at the extremes for the same stay length.

The stay maybe longer on discs because tyre clearance can be much greater with discs but you need a longer stay to take advantage of it.

neeb

apreading wrote:

Its also countered by the BB386 on my bike - a wider bottom bracket with external bearings that fixes all the problems with press fit/BB30 while retaining the larger bearings and at the same time fixes the chainline with wider axles.

Presumably the q-factor is greater in that case then? Either that or the chainline will be the same as with any other BB.

neeb

meanredspider wrote:

And a disc cassette is the same as a rim cassette. The chain line will be exactly the same as the a rim brake bike at the extremes for the same stay length.

The stay maybe longer on discs because tyre clearance can be much greater with discs but you need a longer stay to take advantage of it.

The cassette is the same but (I assume, correct me if you have solid evidence to the contrary) it will be a few mm further out in relation to the centre line of the bike. Presumably about 3.5mm (half of the difference between 135 and 142mm).

thistle_

A couple more observations after going riding today:
* Stopping power in the wet is great, but your tyres can't handle it.
* Big descents can cause brake fade, especially when you're on the brakes all the way because it's wet and need to keep speed in check. Only happened once and they came back after about 10 seconds of cooling down.
* Easy to attach clip on mudguards as there's no brake caliper to avoid for better coverage.
* They sqeual like hell when worn out, which is probably as good thing
* Pads are caliper specific: I have different calipers F&R, everywhere seems to stock the front pads but the rear are harder to find which is bizarre as they are common as muck.
* Inserting wheels requires more skill (but still not much)
* Wheels need more careful packing in cars/bags to make sure the rotor doesn't get bashed and bent.

apreading

neeb wrote:

And it's true (I think?) that with wider dropouts and disc wheels the cassette will be shifted slightly outwards relative to the chainset (assuming q factor is the same), and so chain lines will more crossed at the extremes. That's why most disc frames have slightly longer chainstays (to counteract that), which potentially leads to less drivetrain stiffness.

meanredspider wrote:

The stay maybe longer on discs because tyre clearance can be much greater with discs but you need a longer stay to take advantage of it.

As I understood it, the longer chainstays are primarily to avoid a) heel strike (normal length at a wider angle would cause issues with this) and b) chainring clearance (I think some of the planet-x bikes didnt have a long enough chainstay so they had to limit the size of rings you could use. The need for this can be lessened by concave chainstays though.

meanredspider

Article about chain stays which seems to capture it all well from a large custom bike builder

https://www.sevencycles.com/chainstay-philosophy.php