Compass Cycles on disk brakes

[mcteague]

Not trying to start any arguments, just thought you might like to read Jan's POV. No surprises here though.

https://janheine.wordpress.com/2018/07/12/myth-12-disc-brakes-work-better-than-rim-brakes/

Tim

[eddief]

and un-self-serving.

[Clean39T]

Not too far off from what Dave Kirk had to say in the builder-spotlight thread recently..

Here [https://forums.thepaceline.net/showpost.php?p=2391402&postcount=1066]

That's a big question and I have trouble with a simple answer. I think both rim and disc brakes are great and that one isn't better than the other. That said I think certain brakes are better suited to a particular application.

I think if you want to use a tire that's too wide to fit under a brake caliper, you are riding in the slop, snow or rain consistently, you are riding in the high mountains with long steep descents while using carbon rims.....etc.....then disc brakes are probably the better choice.

If you are riding on flat or rolling terrain, in the dry, with tires that aren't super wide and your biggest braking concern is not hitting your garage door when you get home then rim brakes might be the best choice.

Each brake type is a compromise. Disc brakes flat out work better....but they come with a few downsides (weight, complexity, noise when wet, frame and fork stiffness) and if the downsides outweigh the upside of better braking then it makes little sense to go discs in my opinion.

I hope that makes sense.

dave

and here [https://forums.thepaceline.net/showpost.php?p=2392008&postcount=1073]

I'm not sure I fully understand your question but I'll do my best to answer it and hopefully it will be in the ballpark.

With rim brakes the braking load is distributed and carried far from the center of wheel rotation and is generally carried by two fork blades in the front and two seat stays in the rear. The fork crown and rear brake bridge are far from the hub so the loads are pretty low and easy to deal with.

When we go to disc brakes this changes in a huge way. First the brake loads are imparted to the frame and fork very close to the center of rotation so the forces are much greater. Secondly the brake loads are carried by only one side of the fork or frame which is very asymmetric. This is a big deal both front and rear but the real challenge is the front. The brake loads being put on just one blade and low on that blade mean that the blade needs to be a good bit stiffer and stronger to deal with it well. This means that the fork needs to be substantially stiffer and heavier to work with discs properly. The downsides to this should be obvious - the fork is heavier than it would otherwise be and the stiffness is greater than it would need to be otherwise. So weight and ride both suffer.

The same thing happens in the rear....the brake side chain stay (and maybe seat stay depending on brake type) needs to be heavier and stiffer. The rear end being a closed triangle helps but does not eliminate the issues.

So in the end....all things being equal....a disc frame and fork need to be stiffer and heavier to work properly. Will everyone notice it? No...I doubt they would. I sometimes ride with guys who will not notice that their tire is nearly flat let alone how stiff the fork is....but for some it will be a real downside and something that can be felt.

I've typed a lot of words....I hope some of them address your question!

dave


That's about all the info I need to make a decision on what I'll do for my first custom...

[pncguy]

Wait. What?

"The best rim brakes are lighter than discs, while offering plenty of stopping power and more linear modulation."

I thought disc brakes provided better modulation. Having never ridden discs, I'll need the forum to tell me which is true.

[joosttx]

this is how I see it.

Great rim brakes with great brake tracks that are adjusted correctly are great. Discs brakes are great.

[ltwtsculler91]

Wait. What?

"The best rim brakes are lighter than discs, while offering plenty of stopping power and more linear modulation."

I thought disc brakes provided better modulation. Having never ridden discs, I'll need the forum to tell me which is true.

Linear is the key word here: Rim brakes have a direct relationship between how hard you're pulling on them and how much stopping force is generated. With a disc, they hydraulics mean that braking force doesn't build at the same rate as your hand effort.

I personally feel more in control of my braking effort with rim brakes because of this, I squeeze more, lever travel gets "harder", and then I get more brake power. Discs don't have that linear engagement, it's more on and off.

[Mark McM]

Wait. What?

"The best rim brakes are lighter than discs, while offering plenty of stopping power and more linear modulation."

I thought disc brakes provided better modulation. Having never ridden discs, I'll need the forum to tell me which is true.

"All generalizations are false, including this one" - Mark Twain

Some disc brakes provide very good modulation. Some disc brakes provide poor modulation. For example, my Campagnolo Record rim brakes (which have ball bearing pivots) provide much better modulation than my Avid BB7 Road mechanical disc brakes.

[Mark McM]

Linear is the key word here: Rim brakes have a direct relationship between how hard you're pulling on them and how much stopping force is generated. With a disc, they hydraulics mean that braking force doesn't build at the same rate as your hand effort.

Huh? Since when are hydraulics not linear?

Both cables and hydraulic lines by themselves are inherently linear. The linearity of rim brakes and disc brakes depends on the mechanics of actuators at the ends of the cable or hydraulic lines. For example, low profile cantilever brakes are inherently non-linear, and proper setup is required to minimize their non-linearity. However, caliper brakes (rim or disc) tend to be quite linear.

[christian]

Linear is the key word here: Rim brakes have a direct relationship between how hard you're pulling on them and how much stopping force is generated. With a disc, they hydraulics mean that braking force doesn't build at the same rate as your hand effort.

I personally feel more in control of my braking effort with rim brakes because of this, I squeeze more, lever travel gets "harder", and then I get more brake power. Discs don't have that linear engagement, it's more on and off.

No, that's not how that works. Hydraulics are, if anything, more linear than rim brakes as hydraulic oil compresses about 0.5% per 1000 psi or so. That's substantially less than cables and pivots stretch in standard rim brakes.

[bikinchris]

Y'all can fight it all y'all want. Disc brakes are coming.

[Mark McM]

Y'all can fight it all y'all want. Disc brakes are coming.

That question is no longer in debate, and to a large extant they are already here. The question still be answered is, will they completely replace rim brakes, even in situations where rim brakes are more appropriate?

[Jaybee]

What’s the threshold for “completely replace”?

I mean, you can still get 6speed freewheels if you want.

[Mark McM]

What’s the threshold for “completely replace”?

All high-end bikes from the major manufacturers.



I mean, you can still get 6speed freewheels if you want.

Sure - but they aren't Dura-Ace or Record quality. Or even Ultegra, 105, Chorus, or Potenza quality, either.



There was a short time period when 650c wheel bikes were fairly common and widely available. Although made in many frame sizes, these wheels were particularly advantageous to those that rode small sized bikes. Today, new 650c wheel bikes are hard to find, even though this wheel size is still an advantage to small sized riders. Sure, you can get a custom frame built for 650c wheels - but the there is scant availability of 650c tires, especially at the high quality end (and not much of selection of 650c wheels, either). Although there is still a place for these small sized wheels, they aren't a practical alternative for many who would benefit from them, because the tire and wheel manufacturers have decided that they can make more money selling 700c wheels. The way the industry is going, it seems the same will happen with rim brake bikes.

[zennmotion]

I am a fan of Paul Racer centerpulls that, in dry weather on alu rims, work well and I can't imagine needing anything "better". Even in wet weather and real hills, still work well. Until yesterday. A few days ago I switched out my "gravel" wheels with 35c tires for my roadie wheels with 28s. Yesterday I put the bike in the car on a gorgeous day for a ride on Skyline Drive/Blue Ridge parkway and for a change I decided to start at the top of the first big climb, rolling downhill on a nice fast 6-8% grade. Soon after reaching speed I tried to brake, and I got nuttin', no brakes. At all. :help: I had forgotten to re-attach the transverse cables. The bottom of the hill was a series of sharp twisting turns that I would definitely need to brake for, at the very least drift way over into the opposite lane on a couple of blind corners. I didn't die only because I managed to pull hard, with my hand on the front brake cable, engaging one brake shoe a little, while totally ruining a shoe (thank Dog it was a MTB shoe with lugged soles) dragging it on the pavement, and aiming for a grassy stretch along the road where I managed to slow from nearly 40mph to 15 as I hit the grass and tumbled with just a bruised up hip and some grass stained road rash. What an idiot! I'm thinking of running coaster brakes on all my bikes.

[weiwentg]

Linear is the key word here: Rim brakes have a direct relationship between how hard you're pulling on them and how much stopping force is generated. With a disc, they hydraulics mean that braking force doesn't build at the same rate as your hand effort.

I personally feel more in control of my braking effort with rim brakes because of this, I squeeze more, lever travel gets "harder", and then I get more brake power. Discs don't have that linear engagement, it's more on and off.

So, I switched from a Chorus 10s groupset with differential brakes to R8000 on the same frame.

Comparing the two types of rim brakes, I think I could take your paragraph and substitute R8000 rim brakes where you say hydraulic discs. The braking force builds much faster with the R8000s. I feel like I have less modulation. Others have already given examples of discs with good modulation. Were you were trying to convey something else?

(Note: I have no experience on hydraulic discs. I had Avid mechanical discs when I tried out mountain biking 15 years ago. I could be wrong.)

[mktng]

i love my shimano road hydro brakes. they modulate. they are not grabby. they bite hard when you pull the lever hard. they brake soft when you feather the lever.

i also love good rim brakes.

if i had to have 1. id just keep the hydro discs.

[ltwtsculler91]

Huh? Since when are hydraulics not linear?

Both cables and hydraulic lines by themselves are inherently linear. The linearity of rim brakes and disc brakes depends on the mechanics of actuators at the ends of the cable or hydraulic lines. For example, low profile cantilever brakes are inherently non-linear, and proper setup is required to minimize their non-linearity. However, caliper brakes (rim or disc) tend to be quite linear.

Effort is linear though. You get more feedback to how hard you're pulling versus braking on a Caliper or Canti, whereas the Hydro is very low lever effort for given braking power.

Maybe that makes more sense? I know what I'm trying to say in my head and maybe just not using the terms right

[David Kirk]

yow - my pulse went way up just reading this.

I had something similar happen when I was a young man on a BMX bike. We'd all race down a local hill in a silly test of bravery and I got toward the bottom and needed to brake hard with the single rear brake to avoid heading into an intersection and when I pulled on the brake the cable snapped off at the button in the brake lever. I was going a solid 30mph and headed into a busy intersection. I hopped up the curb onto a grassy lawn and lay the bike way over Mert Lawill style and slid on the grass to a stop.

Think of this makes my pulse even higher.

dave


I am a fan of Paul Racer centerpulls that, in dry weather on alu rims, work well and I can't imagine needing anything "better". Even in wet weather and real hills, still work well. Until yesterday. A few days ago I switched out my "gravel" wheels with 35c tires for my roadie wheels with 28s. Yesterday I put the bike in the car on a gorgeous day for a ride on Skyline Drive/Blue Ridge parkway and for a change I decided to start at the top of the first big climb, rolling downhill on a nice fast 6-8% grade. Soon after reaching speed I tried to brake, and I got nuttin', no brakes. At all. :help: I had forgotten to re-attach the transverse cables. The bottom of the hill was a series of sharp twisting turns that I would definitely need to brake for, at the very least drift way over into the opposite lane on a couple of blind corners. I didn't die only because I managed to pull hard, with my hand on the front brake cable, engaging one brake shoe a little, while totally ruining a shoe (thank Dog it was a MTB shoe with lugged soles) dragging it on the pavement, and aiming for a grassy stretch along the road where I managed to slow from nearly 40mph to 15 as I hit the grass and tumbled with just a bruised up hip and some grass stained road rash. What an idiot! I'm thinking of running coaster brakes on all my bikes.

[Jaybee]

I am a fan of Paul Racer centerpulls that, in dry weather on alu rims, work well and I can't imagine needing anything "better". Even in wet weather and real hills, still work well. Until yesterday. A few days ago I switched out my "gravel" wheels with 35c tires for my roadie wheels with 28s. Yesterday I put the bike in the car on a gorgeous day for a ride on Skyline Drive/Blue Ridge parkway and for a change I decided to start at the top of the first big climb, rolling downhill on a nice fast 6-8% grade. Soon after reaching speed I tried to brake, and I got nuttin', no brakes. At all. :help: I had forgotten to re-attach the transverse cables. The bottom of the hill was a series of sharp twisting turns that I would definitely need to brake for, at the very least drift way over into the opposite lane on a couple of blind corners. I didn't die only because I managed to pull hard, with my hand on the front brake cable, engaging one brake shoe a little, while totally ruining a shoe (thank Dog it was a MTB shoe with lugged soles) dragging it on the pavement, and aiming for a grassy stretch along the road where I managed to slow from nearly 40mph to 15 as I hit the grass and tumbled with just a bruised up hip and some grass stained road rash. What an idiot! I'm thinking of running coaster brakes on all my bikes.


Glad you are still with us!

I was going to point out that you can’t do this with discs, but then remembered the time I left the garage with both of the set screw locks on my HYRDs engaged. Thankfully I was going uphill when I realized it and coasted to a stop.

[bikinchris]

I don't live in an area with a need for powerful, fade resistant brakes. It is pool table flat here and the biggest hills around are overpasses. I can't claim to have ridden every kind of brake available, but I know I have felt some disc brakes that weren't very good as well as rim brakes that were great.

But hands down, there is NO debate in my mind that the best hydraulic disc brakes are far better than the best rim brakes I have ever ridden.

But many people don't ever need the best brakes of any kind. I know I'm not fast enough, nor do I even train or race anymore.

The only question is if the price of decent quality disc brakes can come down low enough to take over all moderate to high level bikes.

[tommyrod74]

The only question is if the price of decent quality disc brakes can come down low enough to take over all moderate to high level bikes.

I think this is going to happen far sooner than later. If you ride MTB, and have ridden a midrange bike lately, you know that even Deore-level brakes work almost exactly like XTR, though obviously heavier. It's astounding how good the cheap hydraulic brakes are now.

Maybe the more germane question is: can they make them light enough, cheaply enough, while working well enough? Dura-Ace (what I have currently) discs are amazing and more than light enough; will Tiagra eventually be also?

[simonov]

Wait. What?

"The best rim brakes are lighter than discs, while offering plenty of stopping power and more linear modulation."

I thought disc brakes provided better modulation. Having never ridden discs, I'll need the forum to tell me which is true.

My take, having both types of brakes, is that the amount of lever pull needed to go from no brake to all brake is much less with hydro discs. So while hydro discs are technically more linear, there is much less room within the range to modulate. I've accidentally locked up my wheels multiple times on my disc bike and I can't remember the last time I did that on a rim brake bike. I'm also just comparing shimano's first gen road hydro disc as that's the only one I've ridden. I'd also bet that if I only rode hydro disc I would get accustomed to the shorter pull and it would become a non-issue. That said, I still prefer rim for most of my riding.

[tylercheung]

The one question I have is - w/ long descents, down, say, So Cal canyon/mountain roads, how much danger would rim brakes have on generating so much heat to melt the inner tube/tire? Or is this a myth?

[adampaiva]

i've done something like this once or twice, though luckily with my bike it would usually just be the front brake that I undo when putting the bike on the roof rack. Without really thinking about it part of my first couple seconds of riding routine is to give a quick pull of each brake just to make sure I have the stopping. You might do the same from now on without thinking about it.

I am a fan of Paul Racer centerpulls that, in dry weather on alu rims, work well and I can't imagine needing anything "better". Even in wet weather and real hills, still work well. Until yesterday. A few days ago I switched out my "gravel" wheels with 35c tires for my roadie wheels with 28s. Yesterday I put the bike in the car on a gorgeous day for a ride on Skyline Drive/Blue Ridge parkway and for a change I decided to start at the top of the first big climb, rolling downhill on a nice fast 6-8% grade. Soon after reaching speed I tried to brake, and I got nuttin', no brakes. At all. :help: I had forgotten to re-attach the transverse cables. The bottom of the hill was a series of sharp twisting turns that I would definitely need to brake for, at the very least drift way over into the opposite lane on a couple of blind corners. I didn't die only because I managed to pull hard, with my hand on the front brake cable, engaging one brake shoe a little, while totally ruining a shoe (thank Dog it was a MTB shoe with lugged soles) dragging it on the pavement, and aiming for a grassy stretch along the road where I managed to slow from nearly 40mph to 15 as I hit the grass and tumbled with just a bruised up hip and some grass stained road rash. What an idiot! I'm thinking of running coaster brakes on all my bikes.

[weaponsgrade]

I am a fan of Paul Racer centerpulls that, in dry weather on alu rims, work well and I can't imagine needing anything "better". Even in wet weather and real hills, still work well. Until yesterday. A few days ago I switched out my "gravel" wheels with 35c tires for my roadie wheels with 28s. Yesterday I put the bike in the car on a gorgeous day for a ride on Skyline Drive/Blue Ridge parkway and for a change I decided to start at the top of the first big climb, rolling downhill on a nice fast 6-8% grade. Soon after reaching speed I tried to brake, and I got nuttin', no brakes. At all. :help: I had forgotten to re-attach the transverse cables. The bottom of the hill was a series of sharp twisting turns that I would definitely need to brake for, at the very least drift way over into the opposite lane on a couple of blind corners. I didn't die only because I managed to pull hard, with my hand on the front brake cable, engaging one brake shoe a little, while totally ruining a shoe (thank Dog it was a MTB shoe with lugged soles) dragging it on the pavement, and aiming for a grassy stretch along the road where I managed to slow from nearly 40mph to 15 as I hit the grass and tumbled with just a bruised up hip and some grass stained road rash. What an idiot! I'm thinking of running coaster brakes on all my bikes.

I think I would've soiled myself. I've had a few times where I forgot to reattach the front straddle cable when transporting my bike via a fork-mounted roof rack. I remember the panic when grabbing the front brake only to realize I'm grabbing air. But luckily I still had the rear brake so things never got too dicey.

[Mark McM]

My take, having both types of brakes, is that the amount of lever pull needed to go from no brake to all brake is much less with hydro discs. So while hydro discs are technically more linear, there is much less room within the range to modulate. I've accidentally locked up my wheels multiple times on my disc bike and I can't remember the last time I did that on a rim brake bike. I'm also just comparing shimano's first gen road hydro disc as that's the only one I've ridden. I'd also bet that if I only rode hydro disc I would get accustomed to the shorter pull and it would become a non-issue. That said, I still prefer rim for most of my riding.

Lever force to brake force is a matter of system leverage ratio. There is no inherent reason that a disc brake has to have a higher leverage ratio than a rim brake (although many do). As an example, Avid makes two cable actuated disc brakes, one for MTBs, and one for road bikes, because MTB levers and road levers different leverage ratios. If you mated the MTB caliper with the road lever, you'd find that it had excessive leverage, and the wheels would lock with little lever force. If you mated the road caliper with an MTB lever, you'd find that you'd need much more lever force to generate the same braking force.

Changing disc size also changes leverage ratio. A larger disc will increase overall leverage ratio, and smaller disk will decrease leverage ratio. On the disc brake you have used, did it use large discs?

[zennmotion]

The one question I have is - w/ long descents, down, say, So Cal canyon/mountain roads, how much danger would rim brakes have on generating so much heat to melt the inner tube/tire? Or is this a myth?

From experience, at least on a tandem, it's not a myth. I experienced a heat caused blowout once on a rear tire, and not even really going very fast (the slow speed on a long steep descent may be the reason it happened- I take it easy with precious cargo in the stoker seat!) I never used to use the added rear drum/drag brake much, now I do! But I remember much discussion regarding disc brakes and tandems when they were first coming out, around the problem of heat and fading. Now nearly all tandems have them, was the heat problem a myth or have the brakes or brake pads improved? Or are rim brakes with a back up drum brake still the best option despite marketing?

[Mark McM]

The one question I have is - w/ long descents, down, say, So Cal canyon/mountain roads, how much danger would rim brakes have on generating so much heat to melt the inner tube/tire? Or is this a myth?

This depends a lot on both braking technique and rider size. Continuously dragging the brakes will generate a larger heat load, so ironically a more cautious descender that drags their brakes to limit speed actually has a greater danger of overheating the tires/brakes. And larger rider obviously generates more energy (which translates into more heat). These are why tire/brake overheating problems are far more common for timid descenders, and for tandems (which generate twice the brake heat).

I haven't descended any California canyon roads, but I have done some long steep twisty descents in New England. Specifically to test brake heating, I rode a rim brake bike down Mt. Ascutney (3.7 miles at an average grade of 12%). This narrow road is open to traffic and goes through a thickly treed forest and has many switch backs. Obviously, I had to do a lot of braking to negotiate the many switch backs and blind corners (much more braking than I usually do on descents). As soon as I hit the bottom I braked hard to a stop, and immediately put my hand on the rims to see how hot they were. They were definitely quite warm, but I wouldn't call them "HOT". Since this experiment, I haven't been too concerned about overheating my rim brakes.

[bikinchris]

I watched a Shimano training video, which detailed how they tested their road brakes for fade. The weighed down a test rider with backpacks etc. and had him ride the brakes hard all the way down steep descents like a scared (sensible?) newby rider to get as much eat as possible.
Compare that to a high performance rider or racer who lets it roll and then slows just enough to carve the corner.

One thing no one is talking about is how disc brake wheels can be made BOTH lighter and stronger with no brake track.

[Davist]

The only question is if the price of decent quality disc brakes can come down low enough to take over all moderate to high level bikes.

it's happened (well sort of) for some brands.. look at Canyon, can only get rim brakes on the ultimates with the DA, Red, or Record groups ($6500+)… Now on the "moderate"/ $3k level ultimate it's disc only (ultegra)

I bought one, lighter than my supersix evo 105 with DA wheels. Per above, fork is sturdy/less compliant, but the ability ride 28s or wider on a "race" frame takes care of that well enough for me

[Mikej]

Ok

[Mark McM]

One thing no one is talking about is how disc brake wheels can be made BOTH lighter and stronger with no brake track.

The reason no one is talking about it is that it is untrue. In fact, the opposite is the case - disc brake wheels are always heavier.

You might be pointing out that weight can be saved on the rim because there is no need for a brake track there. But removing the brake track removes at most only a few dozen grams of material. But there's more to the story than that. Disc brake wheels need longer spokes than rim brakes (because they must be cross laced instead of radial), and usually disc brake wheels have a few more spokes than rim brake wheels. The extra spokes and longer spokes add a couple of dozen grams to the wheel, adding back most of the weight removed from the rim. But then you have to consider that a disc brake hub needs an extra large reinforced flange to mount the rotor, which can add 50 - 80 grams. So in the end, the disc brake wheel ends up being heavier. If you look at any wheel manufacturer who offers the same model of wheels in disc brake and non-disc versions, the disc brake wheels will be about 120 - 160 grams heavier per set.

But of course, that's not a fair apples-to-apples comparison. After all, the rim brake wheels includes the braking surfaces. For a fairer comparison, you'd have to include the weight of the rotors on the disc brake wheel. Rotors (plus their mounting hardware) weigh about 100 - 150 grams each, or 200 - 300 grams a pair. So in reality, the disc brake wheels will weigh 300 - 450 grams more than equivalent rim brake wheels.

Currently, the general consensus is that a disc brake bike will weight about 1 1/2 to 2 lb. more than an equivalent rim brake bike. Roughly half of that is the heavier wheels.

[Davist]

Spoon brakes are the lightest of all, but you may wear out your tires faster... :)

[Burnette]

They have been here for years, they work and look awesome. And that's no myth.

https://2.bp.blogspot.com/-IlRV5yLBBRw/WcNNcCx6OsI/AAAAAAAADRc/C0_05_Tq0F4EGxfg_-ea7KktjNOZ2HP1QCLcBGAs/s1600/BassoBikes_Diamente_SV_Disc_2018_01.jpg
https://bikerumor.com/wp-content/uploads/2018/04/Campagnolo-Super-Record-12-speed_Movement-12_mechanical-shift-hydraulic-disc-brake_road-bike-groupset_Cannondale-Synapse_new-twelve-speed_Canyon-Ultimate-CF-SLX.jpg
http://road.cc/sites/default/files/styles/main_width/public/bianchi-aria-disc-1-v2_0.jpg?itok=G-w3HAUB
[IMG]

[R3awak3n]

campy discs are not even a year old I don't think.
I have some ready to go on a bike, we will see how sweet they are, they look nice-ish but a rim brake bike still looks better.


One thing I can agree with Jan on that article, cable disc brakes are no good. I don't think its worth going to cable disc over rim. Power is not that great, modulation not that great, you get a much heavier system as well for maybe a bit more bite. Hydraulic on the other end, it does offer a few good things.


As far as weights, disc rims are lighter but after the rotor they will be heavier. That is one thing discs are not going to catch up to rim brakes and that is weight. With an EE brake you have pretty nice braking and its 160g for the pair. The shifters are also much lighter when they don't need oil reservoir.

[pbarry]

The shameless plug after "Myth 11" is off-putting. Otherwise the linked post is pretty even handed.

[Burnette]

By "they" why of course it meant the type, been out for years, work and look amazing:

https://www.bicycling.co.za/wp-content/uploads/2018/07/980x553xap6i8467-preview-1531013800-1-1024x578.jpeg.pagespeed.ic.rhzjA3cp8s.jpg
https://coresites-cdn.factorymedia.com/rcuk/wp-content/uploads/2017/07/12-IMG_8106.jpg
https://bikerumor.com/wp-content/uploads/2017/02/2018-BMC-Roadmachine01-limited-edition-gray-europe-only-1.jpg

[bitpuddle]

Linear is the key word here: Rim brakes have a direct relationship between how hard you're pulling on them and how much stopping force is generated. With a disc, they hydraulics mean that braking force doesn't build at the same rate as your hand effort.


I think you’ve got that backwards. Mechanical brakes stretch and flex quite a bit; hydraulic discs very little.

[dddd]

Somehow there is less flex in the system with hydraulic disc brakes, so while the braking force is modulated by the rider, the lever actually hardly moves at all.
This is actually the one parameter by which the world's best brakes are judged, and why the very difficult-to-produce one-piece Monoblock calipers are hot sellers despite their very high cost.

SRAM has sold hydraulic rim brakes for road bikes, I have a few sets that I have yet to install. Perhaps the softer, thicker pads of rim brakes will prevent rim brakes from ever achieving such a rigid braking actuation as hydraulic discs, that and also because the rim itself compressing between the pads.

Rim brakes continue to improve, the latest 8000 and 9100 calipers have a booster plate that anchors the arms from both sides of their pivot bushings/bearings. Carbon rims flex inward more than alloy rims in response to braking forces however.

The problem with disc brakes is that, for any given cost, an equivalent bike is going to be about 1.5 to 2 pounds heavier, and with a more rigid front end.
The benefit of disc brakes is that as wider (especially tubeless) tires and carbon rims enter the picture, the disc brakes lose none of the caliper rigidity or braking issues that rim brakes suffer with, while the ride quality improves.

The fact that most professional road-racing teams are still using rim brakes in the face of their bike sponsor's disc-marketing push, tells us that within the go-fastest environment of roadracing, that rim brakes are still superior.

[bikinchris]

The reason no one is talking about it is that it is untrue. In fact, the opposite is the case - disc brake wheels are always heavier.

You might be pointing out that weight can be saved on the rim because there is no need for a brake track there. But removing the brake track removes at most only a few dozen grams of material. But there's more to the story than that. Disc brake wheels need longer spokes than rim brakes (because they must be cross laced instead of radial), and usually disc brake wheels have a few more spokes than rim brake wheels. The extra spokes and longer spokes add a couple of dozen grams to the wheel, adding back most of the weight removed from the rim. But then you have to consider that a disc brake hub needs an extra large reinforced flange to mount the rotor, which can add 50 - 80 grams. So in the end, the disc brake wheel ends up being heavier. If you look at any wheel manufacturer who offers the same model of wheels in disc brake and non-disc versions, the disc brake wheels will be about 120 - 160 grams heavier per set.

But of course, that's not a fair apples-to-apples comparison. After all, the rim brake wheels includes the braking surfaces. For a fairer comparison, you'd have to include the weight of the rotors on the disc brake wheel. Rotors (plus their mounting hardware) weigh about 100 - 150 grams each, or 200 - 300 grams a pair. So in reality, the disc brake wheels will weigh 300 - 450 grams more than equivalent rim brake wheels.

Currently, the general consensus is that a disc brake bike will weight about 1 1/2 to 2 lb. more than an equivalent rim brake bike. Roughly half of that is the heavier wheels.

When you calculate rotating weight, the tire and rim are rotating weight. The spokes are 50-50 and the hub is not counted as rotating weight. The closer it is to the hub, the less that weight takes to accelerate, like in coming out of a corner or every single pedal stroke climbing a hill. So while disc brakes might make the bike heavier, it doesn't make the rotating mass heavier. Car and motorcycle racing engineers spend lots of money trying to make lighter, stronger wheels. It helps both in accelerating and cornering,

[simonov]

Lever force to brake force is a matter of system leverage ratio. There is no inherent reason that a disc brake has to have a higher leverage ratio than a rim brake (although many do). As an example, Avid makes two cable actuated disc brakes, one for MTBs, and one for road bikes, because MTB levers and road levers different leverage ratios. If you mated the MTB caliper with the road lever, you'd find that it had excessive leverage, and the wheels would lock with little lever force. If you mated the road caliper with an MTB lever, you'd find that you'd need much more lever force to generate the same braking force.

Changing disc size also changes leverage ratio. A larger disc will increase overall leverage ratio, and smaller disk will decrease leverage ratio. On the disc brake you have used, did it use large discs?

Agreed with the part in bold. I don't know why Shimano designed them this way and I know I'm not the only one who feels they're range of engagement, for lack of a better term, is short. I've also heard that the new Campy road discs feel more like rim brakes than the other disc options. I've ridden my disc bike with 140 and 160 rotors. The 160s have more bite when braking hard, but I haven't felt a big difference in how quickly they lock up.

[marciero]

From experience, at least on a tandem, it's not a myth. I experienced a heat caused blowout once on a rear tire, and not even really going very fast (the slow speed on a long steep descent may be the reason it happened- I take it easy with precious cargo in the stoker seat!) I never used to use the added rear drum/drag brake much, now I do! But I remember much discussion regarding disc brakes and tandems when they were first coming out, around the problem of heat and fading. Now nearly all tandems have them, was the heat problem a myth or have the brakes or brake pads improved? Or are rim brakes with a back up drum brake still the best option despite marketing?

Heat dissipation can be a definite concern on tandems in mountainous terrain, whether rim or disc, and depends on several factors such as team weight, braking technique, terrain, rotor size, rotor design (sandwich construction, eg) pad type, etc. The drum brake is the only option that works well as a drag brake, if you like to ride the brakes on a long descent. Both disc and rim are prone to overheating if used as drag; again, depending on various factors.

Regarding discs on production tandems-the same market forces are in play that drive the push to disc brakes on single bikes. Most production tandems seem to come with inexpensive mechanical discs like Avid BB7, which work great but overheating can still be a concern, even with 200mm rotors.
I have mechanical discs on one tandem and and another with Paul mini-V rim brakes. The stopping power is very good on both with perhaps the slight edge to the rim brake Paul's. I have not had problems overheating with either of these tandems, including lots of paved and dirt mountainous terrain. The one exception was some screeching and discoloration on one of the rotors on one very steep and long dirt descent before I switched to ice tech, convincing myself they were better at dissipating heat. I am definitely mindful about not riding them though- letting them cool by alternating left, right, or braking sharply before corners rather than riding them. It helps that my stoker is comfortable with high speeds and aggressive cornering.
I actually removed the drum brake from the rim brake bike because I didnt like the aesthetic or weight.

Lots of stories about this type of thing on tandem forums. The fancy hydro options these days seem to be from from Hayes and Bengal that people seem to like to spec on custom tandems. Bengal has a 10" rotor. Most tandems cannot accommodate a disc this big.

[bikinchris]

10 inch rotors on tandems have been around for many years. Santana being the first.
Years ago, I read a story about a group of tandem riders who rode Mont Ventoux. On their way down, they stopped half way down to let the brakes cool and before anyone could stop her, one of the wives said "how hot are they?" and burnt her finger pretty badly touching the huge rotor.

BTW, Shimano claims their newest rotors will run as m6ch as 212 degrees cooler under heavy braking.

[NHAero]

I'm not yet convinced for road racing bikes in most conditions that discs confer an advantage. I have a wide variety of brakes on bikes. The Ultegra 6700 rim brakes on the CAAD10 are the best rim brakes I've used so far and in my riding see no need to change them. My Bob Jackson all-rounder runs 700C converted from the original 27 inch rims and I run the Tektro R559 long reach calipers, which are noticeably less powerful brakes. My Big Dummy has Avid MTB BB7s and a 203mm front rotor and they work great but squeal amazingly. My Litespeed MTB converted to dropbar has Avid Road BB7s and compressionless housing and I found that the light KCNC rotors didn't cut it, I needed heavier rotors to get good braking. My Pivot MTB has XT hydros, they are just awesomely great brakes, and I haven't done anything to them in almost three years. Finally, my Anderson is recently converted to Shimano hydros, RS685 shifter/levers and RS785 calipers. They're the best road bike brakes I've ever used, easy to set up, and they make using the 37mm tires easy and I can do all braking from the hoods. This is what I'd choose for an all-day ride, but I wouldn't bother putting them on the CAAD10 with its 25mm tires.

The biggest pain about hydro discs is that when I take one of those bikes in my small car and have to remove the front wheel I keep a bit of cedar shingle in the car to wedge between the pads so I don't inadvertently bump the lever and pop the pads out.

[marciero]

10 inch rotors on tandems have been around for many years. Santana being the first.
Years ago, I read a story about a group of tandem riders who rode Mont Ventoux. On their way down, they stopped half way down to let the brakes cool and before anyone could stop her, one of the wives said "how hot are they?" and burnt her finger pretty badly touching the huge rotor.

BTW, Shimano claims their newest rotors will run as m6ch as 212 degrees cooler under heavy braking.

Also stories of stokers, often through tears, using water bottle to spray the rims/rotors in effort to cool them.

The Santana are designed for that Bengal disc, and may have been the impetus behind the Bengal design, to be paired with rim brake front.

Am interested in the new shimano, will have to check that out.

[Mark McM]

When you calculate rotating weight, the tire and rim are rotating weight. The spokes are 50-50 and the hub is not counted as rotating weight. The closer it is to the hub, the less that weight takes to accelerate, like in coming out of a corner or every single pedal stroke climbing a hill. So while disc brakes might make the bike heavier, it doesn't make the rotating mass heavier. Car and motorcycle racing engineers spend lots of money trying to make lighter, stronger wheels. It helps both in accelerating and cornering,

Sorry, disc brake wheels still have more inertia than rim brake wheels, and will accelerate more slowly (all else being equal). As you say, when you accelerate, rotating mass adds extra inertia that has to be overcome. But the reduced inertia of lighter rims on disc brake wheels is still far less than the added inertia from the brake rotor (and extra spokes).

The added inertia due to rotating mass is equal the mass times the square of its proportional distance from the center of rotation. Thus, mass at the rim will have about twice the effective inertia as weight as the hub. Because the spokes extend from the hub the rim, their extra effective inertia will be about 1/3 more than their mass. The rotor is at a radius about 1/4 of the wheel radius, so it will have an extra effective inertia about 1/16 more than its mass. All told, the rotating inertia of the extra spokes and rotor cancels out about 2/3 of the inertia reduction of the rim.

The total inertia of the wheel is a combination of its translational inertia (mass) and its rotational inertia (a function of mass and its distance from the center of rotation). The reduction in total inertia due to a rim that is 25 grams less (50 grams effective inertia) is far less than the addition of total inertia due to a hub and rotor that weigh 200 grams more - and that's even if you neglect the rotating inertia of the rotor.

And as far as the effect of rotating inertia on climbing, that's an old myth - its been well proven that only mass matters when climbing, not rotating inertia. And the reason that wheel weight matters to motor racers (cars and motorcycles) is not so much due to rotating inertia, it due to the need to keep the tires pressed firmly to the pavement: These vehicles have suspension, and the wheels are unsprung weight - the greater their mass, the slower they react to changes in pavement.


In the big picture, the extra mass and inertia of disc brake bikes is just a small percentage of the total mass and inertia. It is really only consequential to those who race up hill. Other factors are far more important to choosing brake type. But claiming that disc brakes have some type of weight or acceleration advantage is just wrong.

[mcteague]

As both the fork and rear stays need to be redesigned for disk brakes I wonder if the frame builders have enough experience to beef them up but still maintain ride quality. I suspect many just added more material, to strengthen things, and called it a day.

Tim

[Climb01742]

Not trying to start any arguments...

No worries. Arguments start here without anyone trying...;):)

[Clean39T]

No worries. Arguments start here without anyone trying...;):)

One man's argument is another man's enjoyable discussion.

As long as it stays civil, what's wrong with some good back'n'forth?

[josephr]

That question is no longer in debate, and to a large extant they are already here. The question still be answered is, will they completely replace rim brakes, even in situations where rim brakes are more appropriate?

that question is completely irrelevant...my girlfriend, who has essential tremors, not very good hand-strength and a fear of going downhill fast met another female cyclist with essential tremors,not very good hand-strength and a fear of going downhill fast. This other cyclist was extolling the virtues of her hydraulic disc brakes. Now the gf is asking non-stop questions about how much money she needs to come up with to get her a new bike with disc brakes. :help:

[cachagua]

Now the gf is asking non-stop questions about how much money she needs to come up with to get her a new bike with disc brakes. :help:

Tell her it's unclear whether it'd really benefit her, and generously agree to evaluate the technology by riding a prototype made for you.

And if it's good, then she'll only have to spend about the same amount again to get one for herself.

[Climb01742]

One man's argument is another man's enjoyable discussion.

As long as it stays civil, what's wrong with some good back'n'forth?

Two of these;):)weren't enough to clue you in I was being tongue in cheek?

;):);):);):);):) Better?

[Clean39T]

Two of these;):)weren't enough to clue you in I was being tongue in cheek?

;):);):);):);):) Better?Ha ha, I blame Tapatalk

Sent from my Pixel 2 XL using Tapatalk

[Climb01742]

Ha ha, I blame Tapatalk

Sent from my Pixel 2 XL using Tapatalk

;)