Let's talk disc brake road bikes

[325racer]

Some issues I've seen with comparing road bikes is they come in SOOOO many different flavors and visually it's hard to tell them apart.

You've got Race Bikes, Endurance bikes, gravel bikes, cyclo cross bikes, touring bikes, etc, etc.  Then within each variety, each vendor does things a little different.  In the Mtn bike world once you get into a category, things are pretty much the same.

I didn't ride, but sat on the trainer on 2 "Endurance" bikes the other day.  One a BMC Gran Fondo, the other a Cannondale Synapse.  Both were 56cm frame, both were meant for long rides.  The BMC had a very nice wide comfortable (to me) bar, but the seat was set to far back and the bar was to far forward.  The Cannondale, I didn't care for the bar, also sat a little to far back, but not so far it couldn't be adjusted and the bars were much closer to where I'd like them.

While I didn't ride either, I suspect they both rode slightly different as well, but would think shifting, brakes etc would feel the same as they were the same component groups, I didn't ride them (on purpose) but neither had disc brakes, but you could get them on a different version of the same bikes.

I did do a 56 miler last weekend with some friends who are wanting to do more, so I'm thinking about getting my own bike instead of borrowing my fathers, because sooner or later he's going to want it back, even though I probably shouldn't let him do any road rides by himself....

[Sitar_Ned]

Yes. Lots of subtle differences in road frames. How stretched out you are, how aggressively you're leaned forward, etc.. Gets pretty confusing.

[MTNRCKT]

I'm loving the trend of road frames coming with disc brakes.

I'm of the opinion that it would definitely be worth it to build a road specific bike rather than buying some road wheels for your MTB, even if you built it up with a flat bar. The body position and light weight (7-9 lbs will make a huge difference) can't really be replicated with an MTB imo, and like you said, will leave a lot to be desired. Also the road components like Dura-Ace or SRAM Red not only have optimal road gearing but also have a different lighter feel to them. I also suggest you guys give a a reconsideration to drop bars. Everybody uses them for a reason. When you get really comfortable with the various integrated braking and shifting systems from Shimano and SRAM the "oneness" with the bike can't be beat. Also, a tip, do some reading of fitting a road frame too your body. On an MTB you have a little more leeway than you do with a road frame.

[seahog32]

Hi

My name is Karl and I am a roadie (as we say at Roadies Anonynous meetings) and here are my 2 cents from a roadie's perspective.

Road bikes with disk breaks look weird. Now that may be a ridiculous argument but I am very sure that all of you have noticed that a bike look of which you like rides way better. Anyway, this does not seem to bother any of the participant in this thread so we can move on.

Disk breaks are noisy. I don't mean to say horribly noisy but you may/will be surprised by the subtle noises that on a MTB are completely overshadowed by all the trail noises or even by riding knobby tires on the pavement. I am not talking about misalignments affecting the functionality so this is just a warning and we can move further on to the more serious objections.

Disc breaks are not widely used hence not well tested on road bikes. There is a thread on this forum regarding a rigid mtb fork failure. Typical road forks (and to some extent chain- and seatstays too) are way thinner than their mtb counterparts which allows for less real estate to beef them up structurally. Do you feel like relying integrity of your bones and possibly more on untested anonymous chinese products? Crushes are less common, in my case anyway, than when riding mtb's but speeds are much higher and possible consequences more serious. Just a food for thought, you don't need to stone me (yet). I myself am riding a no-name chinese carbon fibre fork on my commuter/cross bike. However, it is a sturdy mtb rigid fork ridden with 40 mm semi-slick tires. It would feel and look inappropriet on my light road bike.

Now the most important issue of the road disc breaks is their functionality. The common argument is the stopping power followed closely by "modulation". Trust me that you can easily lock up your wheels using the common road breaks so that should be no objective. With one exeption though which are the carbon fibre rims in wet conditions. If you are planning on riding your road bike in pouring rain regularly and you insist on using carbon wheels on those days then discs may really be the only borderline sane way to go. Modulation is in my personal opinion more a marketing slogan than a real argument but you may feel different about it. Admittedly, it can be difficult to get used to the regular road calipers for someone used to the disc break feel only.

Finally, if we are talking hydraulic disc breaks, there is the issue of their overheating to the point of failure. Depends on what do you expect to use you road bike for but in the "real" road biking the descends are often way longer  + speeds much higher than what you may be accustomed to as a mountain biker. Road components tend to be smaller due to our obsession with grams and aerodynamics. This likely makes them less effective at dissipating the heat. I don't need to preach to the choir here what are the consequences of the boiling break fluid.

[Sitar_Ned]

Hey Karl, good post. You make a lot of good, well thought out points. Prior to reading your post, I would've considered disc brakes a no brainer, but if I were to do a road build now I'd definitely give serious consideration to conventional rim brakes. Your point about the carbon fiber fork failure makes a lot of sense.. Disc brakes are going to transfer the braking force to the lower blade of the fork that would usually be absorbed at the crown of the fork where traditional rim brakes mount. If road oriented carbon forks are less beefy then their MTB counterparts, then maybe transferring those forces down there isn't such a great idea. This is, of course, more applicable if you're going to be flying down paved mountain roads at 50 mph (which I most likely wouldn't be).

That said, it could be the case that the carbon road forks are perfectly capable of handling the braking forces. You cited the example of the MTB fork that failed here, and while that does indeed serve to backup your point, perhaps the fact that fork had been ridden through rocky, unforgiving MTB terrain had more to do with the failure than the braking force? Are there many known incidents where these forks failed on a road bike due to disc brakes?

I'm not claiming you're wrong; I'm really not sure either way.

[Carbon_Dude]

In my opinion it's still a no brainer, disc brakes are still the way to go and the industry is obviously moving in that direction.  In a few more years, most road bikes will have disc brakes.  Today, most CX bikes and many commuter bikes have disc brakes, most brands have at least a couple disc road bike models.  For me the advantages outweigh the disadvantages.  Disc brakes are what I would have if I got a road bike.  I've ridden both rim, mechanical disc, and hydraulic disc brake equipped road bikes.  I much prefer hydraulic disc brakes on any bike I own. 

1)  A properly designed fork with a disc brake mount can be made plenty strong to resist the braking forces imparted to the rotor.  With carbon fiber technology, a stronger fork designed for a disc brake only weighs a few ounces more.  Non-rim brake wheels therefore can be lighter since they no longer need that braking surface.

2)  On my carbon rim, I would rather wear a brake pad against an inexpensive rotor instead of a disc brake pad against my high dollar carbon wheels.

3)  Overheating isn't a big issue, the rotor and caliper are out in the airstream, hydraulic brakes can use high temp fluid, pads have aluminum fins for sinking heat.  Downhill bikes generate massive braking forces, no issues with overheating brakes there.  Not to mention, with any braking application, the user needs to be smart with how they use their brakes, rim or disc, the user can cause any number of issues with improper application of brakes.

4)  In the wet, disc brakes work infinitely better than rim brakes.

5)  If I have a rim that is slightly out of true, no problem for disc brakes.

6) Disc brakes are well tested on mountain bikes, CX bikes, road bikes, motorcycles, ebikes, an countless other forms of transpiration.  Other than the need to  make a fork and hub a bit stronger, which has been done on all the new disc road and cyclocross bikes, it's a well known technology that is safe and reliable.

BTW, seahog32, not sure if English is your first language, but "break" is not the correct word for a mechanism that slows or stops a rotating wheel.

[carbonazza]

David Millar is quite against disc brakes and may have a strong point.
A pity the page looks like a car ad but there are some interesting bits:
http://road.cc/content/feature/149577-david-millar-changing-technology-pro-peloton-and-whether-disc-brakes-have

I understand that the small tire patch can't handle the full stopping power of the brake.
But I still think the combination of both more power and a smaller diameter will offer much more modularity before blocking the wheel.

[Carbon_Dude]

Most any brake, even a poor one will lock the wheel given the small contact patch of a road bike tire.  That's why disc brakes are not about stopping power, it's all about the other benefits that come  along with a better brake design.

[cmh]

Road bikes with disk breaks look weird...

Road bikes with sloped top tubes looked weird until they were fashionable.

Disk breaks are noisy...

Although anything with the name "Avid" seems to howl like a mournful dog in the wet, I don't find this to be the case, including my 'cross bike which I ride on the road.

Disc breaks are not widely used hence not well tested on road bikes.

...but have been widely used and tested many, many other places.

...Typical road forks (and to some extent chain- and seatstays too) are way thinner than their mtb counterparts which allows for less real estate to beef them up structurally...

In the case of the "anonymous chinese products" I'd tend to give you this one, but carbon can do some pretty wonderful things if it's designed and used properly, so I'm not so concerned about this, at least from the big brands for the foreseeable future.

Now the most important issue of the road disc breaks is their functionality. The common argument is the stopping power followed closely by "modulation". Trust me that you can easily lock up your wheels using the common road breaks so that should be no objective. With one exeption though which are the carbon fibre rims in wet conditions. If you are planning on riding your road bike in pouring rain regularly and you insist on using carbon wheels on those days then discs may really be the only borderline sane way to go. Modulation is in my personal opinion more a marketing slogan than a real argument but you may feel different about it. Admittedly, it can be difficult to get used to the regular road calipers for someone used to the disc break feel only.

I've ridden a bike with some borderline terrifyingly bad (rim) brakes. I could still lock up the rear tire. I don't get how everyone uses that as the benchmark of brake performance. (Also, the odds are REALLY good that you can't lock up your front wheel with any brakes.) What made those brakes terrifying was loads of squish in the levers with very little braking force until it was getting near lockup. Slowing predictably with those was... interesting.

Finally, if we are talking hydraulic disc breaks, there is the issue of their overheating to the point of failure. Depends on what do you expect to use you road bike for but in the "real" road biking the descends are often way longer  + speeds much higher than what you may be accustomed to as a mountain biker. Road components tend to be smaller due to our obsession with grams and aerodynamics. This likely makes them less effective at dissipating the heat. I don't need to preach to the choir here what are the consequences of the boiling break fluid.

This I agree with wholeheartedly. Back in 2012, BikeRumor did a bit on disk brakes on the road after one of their editors had a big crash after brake failure that kinda summarizes most of my concerns with road disks. So many folks focus on the small contact patch of a road tire and miss the fact that that small contact patch gives far, far more grip than the comparatively huge contact patch of MTB tires, even knobbies on the road. Combine that with higher speeds and potentially longer descents and heat is a real issue.

David Millar says we don't need disk brakes. Pros said we didn't need carbon fiber and a whole bunch of other things that they insist on now. If anything, it seems like road pros are the slowest to adopt something new. He also says how great rim brakes are now - sure is nice when you don't have to pay for Shimano's Dura Ace and all the other super high end parts, and someone else builds the bikes for you. Plus, the guy is the "cycling ambassador" for Maserati. I wonder what he thinks about rim brakes on his car?

[325racer]

I'm still keeping an eye on this.  For an endurance road bike, discs are the way to go in the future.  I got a quote from Peter, but I'm waiting to see the final specs on the 56cm 092 frame.  I would build it up with Ultegra components and a set of carbon wheels.  I will probably source the stem and bars locally, actually I already have a stem I'd probably use, although it's red, I think my build would be using black components.  For a Bar, I think I need something in a 460, which narrows down the choices.

I'm envisioning something fully painted with some stripes masked so the carbon will come through as stripes or something....  Coloring will probably be all white, some sort of metallic blue or maybe a combination.

[seahog32]

I am using both kind of brakes regularly. I don't feel any particular need to play an advocate to either of the sides. I would be similarly likely to point out advantages of disk brakes on a traditionalist road bike forum. I have no intention trying to change the minds of people who have already made them up. I simply believe that both sides need to be heard before making a decision. What I wrote above was just a short list of concerns that you can typically hear in the road cycling world that someone not quite familiar with road bikes may want to take in consideration before jumping on the train. I personally  find some of them a bit ridiculous. Sorry if I did not make myself clear enough about that.

That said, I must admit that I am actually one of those who find the look of disk brakes on a road bike to be "wrong". That is of course completely irrational view. I mentioned that one just to show that some arguments against them are rather laughable and I am mentioning it again to show that I may be biased. On the other hand, I got quite comfortable using disc brakes on my commuter hybrid (Spesh Crosstrail) with a no-name Chinese carbon (MTB) fork. If anybody is interested, my commute in the morning includes 700 meters over less than 10 km of a continuous descend. Due to shortage of time I do that on a highway while coming home in the afternoon I enjoy the luxury of a mixture of paved back roads, gravel FSR's and singletrack trails. The point of "knowing how to use"  hydraulic brakes on a long descend is quite obvious. However, sometimes it is not reasonably safe for me to pass those pesky logging trucks whose (strangely sane) drivers insist on not going any faster than 60km/h on that descend and thus I am forced to drag/ride the brakes whether I like it or not. The discs tend to get quite hot in the process (to the point that the spit boils on them instantly). Never had any problems with brakes performance but would not be comfortable pushing them much further (like on a descend twice that long). Those are MTB brakes, even if rather cheap ones (Shimano M446 if I remember correctly), though, and there is/will be a significant push to make the existing/coming dedicated road bike disc brakes as light and generally as small as reasonable possible. The placement of the reasonability line is rather uncertain at this point IMO. Hence the overheating concern.

It is an indisputable fact that the industry is moving towards road disc brakes. What are the incentives for doing that should stay open for another thread if any one is interested to start it. I am certainly not hearing too many demands for them from the road cyclists but maybe I am struck by selective deafness or some other condition middle aged men are prone to. My wife would be happy to give you the full list, I'm sure.  Anyway, the industry will keep coming with new stuff. Whether it is a real improvement only the time can always tell. Btw. our LBS owner just came back from some bike expo and is raving about the new S-Works Allez. For those who are unfamiliar with the Spesh lineup, Allez used to be the cheap, alloy alternatives to the top of the line carbon road racing frames. Well, not anymore. These frames are supposedly  as light as the carbon models now and likely stiffer. Not trying to bash the carbon here, just a response to the remark that road pros used to be against the carbon when it was first introduced.


I personally am unaware of any disc carbon road bike fork failures. That comes with them being untested in the real (road cycling) world. And sorry, cyclocross does not count. Bunch of short steep hills is not a very typical course profile in road cycling. Strangely, and I am actually honestly surprised in this case, not all cyclocross riders are switching to discs either now when they are UCI legal.


Whether one can and will trust the strength of a carbon fibre fork in general and which fork that would be in particular is a question I leave open, too. I am no hater of China-direct carbon and I think it is a great alternative to the hugely overpriced (and similarly China-made) brandname carbon parts. Maybe I am just not an early adopter. Again, everything I wrote here should be taken only as a food for for thought. I am not speaking from any position of authority. If you are ready then by all means go for it. We need the real world testers after all.

Lastly, before I forget, English is not my first language and, chronologically speaking, not my second, third or forth language either. I am greatly thankful for the free English lesson offered as well as any other that may come in the future.

[cmh]

...And sorry, cyclocross does not count. Bunch of short steep hills is not a very typical course profile in road cycling. Strangely, and I am actually honestly surprised in this case, not all cyclocross riders are switching to discs either now when they are UCI legal.

I think that's a combination of things - retro-grouchiness that is common in top level pros - it's always been done this way, why would I wanna change - as well as a good set of rim cantilevers being lighter than a disk setup. Look at Sven Nys - he has access to disk frames that he'll use if it's REALLY muddy, but he prefers the old design that he knows and is lighter. Racers like Lars Van Der Haar are younger and so less inclined to stick with the old-school stuff.

Lastly, before I forget, English is not my first language and, chronologically speaking, not my second, third or forth language either. I am greatly thankful for the free English lesson offered as well as any other that may come in the future.

I certainly wouldn't have guessed - your English is probably better than mine and it's all I know!

[ibike]

I am curious about that why there is a big hole at the seat tube?Sorry,in fact I agree that there no necessary to equip the disc road bikes ,I think it more suitable for wet days .

[PeterXu]

CS-092 SL frame in 56cm could be ordered to customize and book now.

Attached revised geometry for reference.

[Vipassana]

Oh, I'm very interested in this frame!  I think this might be my next purchase.  Please let us know when you have it listed on your website, Peter.  And when you will have other sizes.  I am either needing a 54 or 56.
 

I am looking to build a decently road bike, but with disks.  My target is 15-16 lbs.