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  1. #1
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    State of road discs

    edit: Whoops! I meant to be posting this in Components and Wrenching - if a mod sees this, please move? thanks.

    Been researching disc brakes for road use recently (I know, I know, but I don't pay attention to bike tech, unless I need to). While I like the idea of discs, the implementation seems hardly flawless; I wrote this post to make a point of the situation while trying to be as objective as possible, including both pros and cons.

    If you think I got something wrong, or forgot anything, please leave a comment. Before clicking the Post button, remember: don't be a dick, please; this is not meant to be neither a disc love, nor a disc hate post or thread.


    • Hydraulic has light action, superior modulation. Adjusts automatically for pad wear. Shimano Ultegra considered to be the best system available currently.
    • Hydraulic more complex than mechanic, potentially more messy. Home mechanic will require a bleeding kit at some point.
    • Hydraulic levers still in the trickling down phase, expensive. More affordable hydraulic levers still using old designs and not that much cheaper. Electronic + Hydraulic super expensive.
    • Hydraulic less affected by freezing, rusting and seizing.
    • Hydraulic lines less sturdy than cables.
    • Standard/affordable mechanic discs are generally sucky: inferior braking; issues with adjustment, alignment, rubbing, wear.
    • Mechanic disc brakes can be pretty decent with good calipers (BB7, Spyre, HY RD), but those are expensive: 1 good rim brake-set costs less than a single disc caliper. HY RD complete brake costs several times as much as a good rim brake-set, unless one only buys Dura Ace parts and think them cheap.
    • Thru axle to be preferred over traditional "Quick Release" aka open fork ends, where hard braking efforts may lead to wheel axle moving and QR getting loose.
    • Thru axle standards derived from MTB; may be overbuilt for road use. Argument extends to hubs.
    • Many different thru-axle standards. Adaptor-fest.
    • Thru-axle/disc wheel replacement more involved than traditional road wheel/rim brakes.
    • Compression-less housing recommended for mechanic calipers, adds to cost.
    • In rain, shorter stopping distance than rim brakes, all else being equal.
    • Rotors and pads may wear out very quickly in adverse conditions.
    • Generally more complex and heavier than rim brakes.
    • Potentially more noisy?
    • Removes some constraints from wheel design, mainly making carbon rims with no brake track possible.
    • Adds some constraints to bike design: sturdier forks, spokes. Front wheel needs to be dished (less sturdy)
    • Rotors and pads cost more, last less than rim brake pads and rims.
    • Rotors and pads more susceptible to contamination than rim brakes.
    • Post mount isn't pretty.
    • Flat mount easier on the eyes, slightly lighter; touch more aero, perhaps?
    • Flat mount designed for 140 mm (seriously?)
    • 160 mm still get freaky hot on tricky descents, i.e. exactly where you'd want discs to be heads and shoulders above traditional brakes.
    • 180 mm rotors only work with post? assuming fork clearance.
    • Flat mount calipers may be more expensive.
    • Post is an adaptor-fest, flat mount less so (less choices).
    Last edited by oct3; 06-12-2017 at 06:02 PM.

  2. #2
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    Quote Originally Posted by oct3 View Post
    edit: Whoops! I meant to be posting this in Components and Wrenching - if a mod sees this, please move? thanks.

    Been researching disc brakes for road use recently (I know, I know, but I don't pay attention to bike tech, unless I need to). While I like the idea of discs, the implementation seems hardly flawless; I wrote this post to make a point of the situation while trying to be as objective as possible, including both pros and cons.

    If you think I got something wrong, or forgot anything, please leave a comment. Before clicking the Post button, remember: don't be a dick, please; this is not meant to be neither a disc love, nor a disc hate post or thread.


    • Hydraulic has light action, superior modulation. Adjusts automatically for pad wear. Shimano Ultegra considered to be the best system available currently.
    • Hydraulic more complex than mechanic, potentially more messy. Home mechanic will require a bleeding kit at some point. Hydraulic is better performing and less maintenance, you'll only have to bleed your brakes when there is an issue or, after a few years if you feel like it. It can be messy, I know more than a few people who just pay a shop a few bucks to deal with it.
    • Hydraulic levers still in the trickling down phase, expensive. More affordable hydraulic levers still using old designs and not that much cheaper. Electronic + Hydraulic super expensive. New bike parts are spendy
    • Hydraulic less affected by freezing, rusting and seizing. Not really an issue with mechanicals, I've been using them since they came out and never had an issue in any season.
    • Hydraulic lines less sturdy than cables. Technically, this might be true, but is a non issue
    • Standard/affordable mechanic discs are generally sucky: inferior braking; issues with adjustment, alignment, rubbing, wear. Not as good as hydraulics, but they still work.
    • Mechanic disc brakes can be pretty decent with good calipers (BB7, Spyre, HY RD), but those are expensive: 1 good rim brake-set costs less than a single disc caliper. HY RD complete brake costs several times as much as a good rim brake-set, unless one only buys Dura Ace parts and think them cheap.
    • Thru axle to be preferred over traditional "Quick Release" aka open fork ends, where hard braking efforts may lead to wheel axle moving and QR getting loose. I'd prefer a TA, but QR's work OK and I've never had a wheel fall out, or get loose since discs first came out.
    • Thru axle standards derived from MTB; may be overbuilt for road use. Argument extends to hubs. Whatever
    • Many different thru-axle standards. Adaptor-fest. Buy smart
    • Thru-axle/disc wheel replacement more involved than traditional road wheel/rim brakes. Put wheel in slot, screw in TA. Hardly brain surgery.
    • Compression-less housing recommended for mechanic calipers, adds to cost. Not necessary
    • In rain, shorter stopping distance than rim brakes, all else being equal. Maybe? Depends on your setup. The main thing is that they provide the same experience in ALL conditions.
    • Rotors and pads may wear out very quickly in adverse conditions. Pads, not rotors, they last a long time.
    • Generally more complex and heavier than rim brakes.
    • Potentially more noisy? If not aligned, sure. I've heard plenty of noisy wet carbon rims with rim brakes.
    • Removes some constraints from wheel design, mainly making carbon rims with no brake track possible.
    • Adds some constraints to bike design: sturdier forks, spokes. Front wheel needs to be dished (less sturdy)
    • Rotors and pads cost more, last less than rim brake pads and rims. Rotors are way cheaper than rims and the wear is comparable. I've never worn out a rotor, but I have rims. Pads are comparable if you're buying decent rim brake pads.
    • Rotors and pads more susceptible to contamination than rim brakes. Don't be an idiot and drip oil on them
    • Post mount isn't pretty.
    • Flat mount easier on the eyes, slightly lighter; touch more aero, perhaps?
    • Flat mount designed for 140 mm (seriously?) Unless you are a featherweight and/or never descend, 140mm is too small.
    • 160 mm still get freaky hot on tricky descents, i.e. exactly where you'd want discs to be heads and shoulders above traditional brakes. All discs get freaky hot on descents, just don't ride them continually and you'll be fine.
    • 180 mm rotors only work with post? assuming fork clearance.
    • Flat mount calipers may be more expensive.
    • Post is an adaptor-fest, flat mount less so (less choices). With post, you either use the mount that came with your brakeset, or buy another if you're going with bigger rotors. And, then you're done. It's not a big deal.
    My edits in red.

  3. #3
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    Whatever you say. In the mean time I'll ride my disc equipped road bike.
    Oh and by the way I have 140 mm rotors on my bike,they get blazing hot but still beats braking with calipers and carbon rims.

  4. #4
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    As a dh mountain biker who took up road biking due to time constraints, I think you're really making mountains out of mole hills. These are all old problems with well known solutions. My trp spyres are nowhere close to my saints but holy ****, **** rim brakes forever.


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  5. #5
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    Btw, I went with mechanical because I didn't want to spend the crazy money to upgrade my di2 shifters.


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  6. #6
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    Flat mount designed for 140 mm (seriously?) Unless you are a featherweight and/or never descend, 140mm is too small.
    I am 175-180lbs and do a lot of technical descending with 140mm F/R disc, hasn't been an issue.



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  7. #7
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    Quote Originally Posted by meeeeep View Post
    Btw, I went with mechanical because I didn't want to spend the crazy money to upgrade my di2 shifters.


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    It is so worth it. The touring/gravel Ti Bik has R785. Wonderful stuff.
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  8. #8
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    Quote Originally Posted by Devastazione View Post
    Whatever you say. In the mean time I'll ride my disc equipped road bike.
    Oh and by the way I have 140 mm rotors on my bike,they get blazing hot but still beats braking with calipers and carbon rims.
    This statement is redundant. Any braking system is better than calipers on carbon rims. Carbon just doesn't make for a very good braking surface.
    Last edited by terbennett; 06-22-2017 at 07:46 AM.

  9. #9
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    Quote Originally Posted by terbennett View Post
    This statement is redundant. Any braking system is better than calipers on carbon rims. Carbon just doesn't make for a very good braking surface.
    Fully agree. I have little interest in spending more money on bikes and my rim brakes work fine. But I have never been so scared as on a rainy descent in a cat 3 road race where a large number of $2 k wheelsets stopped braking. Similarly on long mountain descents in the Rockies I will back off a lot from anyone on carbon clinchers.

    My view is that anyone on carbon clinchers should be using disc brakes.

    Other issues that aren't mentioned enough:

    Brake pad contamination: can ruin a set of brake pads very easily from oil contamination. Plenty of oil on the roads to be splashed up on a rainy ride. Don't encounter this off road.

    Extra spokes required and no radial spoking. Goes against all aero weenie trends.

    Beefy fork needed. My fat bike does pull a bit to the side when I brake on a downhill.

  10. #10
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    Quote Originally Posted by terbennett View Post
    This statement is redundant. Any braking system is better than calipers on carbon rims. Carbon just doesn't make for a very good braking surface.

    The dry braking on my Reynolds carbon wheels with their cryo blue power brake pads was easily as good as the braking with my alloy wheels. Wet braking was bad though.
    Neither are as good as the braking on my disc brake bike, wet or dry

  11. #11
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    Quote Originally Posted by carlosflanders View Post

    Brake pad contamination: can ruin a set of brake pads very easily from oil contamination. Plenty of oil on the roads to be splashed up on a rainy ride. Don't encounter this off road.
    I've ridden my disc in the rain several times with no issues. The one time I did manage to contaminate the pads (which didn't affect the braking, just made them noisy) it took two minutes with some brake cleaner to fix it.




    Beefy fork needed. My fat bike does pull a bit to the side when I brake on a downhill.
    Fork on my disc TCR is no beefier than my non disc TCR. And there is no pulling.


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  12. #12
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    I keep looking for all these rainy day riders in my area... I can never seem to find any.
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  13. #13
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    I have had the good fortune to ride both many times. I have no beef with rim brakes, but if I am descending in wet or dangerous conditions like my life depends on it (which it often actually does), I want hydraulic discs every single time. Yes, yes, I know I could devote the rest of my life to becoming the amateur version of the best world tour descenders, but even some pros don't reach that level and I would like to be able to stop effectively in all conditions in the interim, thank you. I know, I know, some of you never touch your brakes and never think about slowing down, but this mere mortal does and I feel like disc brakes help me do that more efficiently and are a good thing, particularly as they continue to refine designs.

    That being said, I really see promise in the Exalith coating Mavic has been producing for a while. As they embrace wider rims, tubeless setups, and improve their rims and tires, I feel like that braking surface could be another really solid option for both alloy and carbon wheels.

    At the end of the day though, who cares what anyone else thinks? Do what you feel comfortable doing. You are the one that is responsible for your own noggin and the only one on here that has to live with the consequences of the choice you make. The bike I am currently working on building (should be done this week whoo hoo!!!) is a rim brake Ridley Fenix Alloy, but I bought it to be my budget friendly, foul weather/crit type bike. I don't plan on doing a bunch of serious/dangerous climbing and descending on it, so I am fine with that bike having rim brakes. To be honest, I am focused more on gravel events, crits, and Merckx style time trials at this point, so my serious/dangerous climbing and descending days may be behind me at this point. Other than a TT bike, anything else I buy will have discs. No doubt about it. Next on the agenda is a gravel bike, which will be my primary ride, and that will certainly have discs for obvious reasons. The two leaders in the clubhouse are the Ridley X-Trail and the new Specialized Diverge. The Diverge Sport with upgraded hydraulic shifters and a carbon seatpost will likely carry the day.

    https://www.specialized.com/us/en/me...gesport/152240
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  14. #14
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    Quote Originally Posted by DrSmile View Post
    I keep looking for all these rainy day riders in my area... I can never seem to find any.
    I do it a fair bit. I've used all of the braking styles, save drum.

    Hydraulic discs are certainly the most powerful, but they aren't faultless. If you get in really heavy rain, they aren't going to work worth a damn. There's no bite, almost zero braking power (no better than a rim brake), and it's pretty scary when trying to outrun a massive storm. I'm talking a torrential downpour, but that's when you really want good brakes. This has only happened on my MTBs with XT M785s and SLX M7000s. Both of those are otherwise very good, but can't overcome some situations. Pad choice may matter a little here, but not that much.

    I tried mechanical BB7 S road brakes on a CX build, and they weren't great. Not much power, and even though they're designed for it, the lever feel was kind of crappy. Mechanical BB7s on my MTBs were much better. Even 6800 rim brakes are better, and with some salmon Kool Stops, they do surprisingly well in the wet.

    Not to rehash the thru-axle vs. QR debate, but I've used a variety of setups. It makes zero difference. Whatever the bike comes with is fine.

    Maintenance is sort of a non-issue with hydraulic discs. Bleed if you need to, and replace the fluid every few years.

    I've had both mechanical and hydraulic discs freeze/get ice/snow packed. If the caliper gets stuffed with snow, it doesn't matter what's doing the pushing. It's going to take several seconds to get any power, so just plan ahead (if you can).

    I've put thousands of miles on (MTB) rotors, and have never come close to wearing one out. I have dripped mineral oil (brake fluid) on them and ruined the rotor and pads though. That sucked.

    I also run 160/160 on all of my bikes, and I've never felt that they're too small or incapable of dealing with heat buildup. I use Shimano's IceTech stuff though, which may or may not be snake oil. Whatever the case, switching from a mid/low-end Shimano or Avid rotor to an XT/Ultegra-level Ice Tech is a huge improvement though.

    If I were getting a new road-ish bike, Shimano hydraulic discs would be my preference. In most situations though, there's not a whole lot of noticeable difference between those and good rim brakes. Road rim brakes have always been an order of magnitude better than any other type of rim brake.

  15. #15
    Not a climber
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    Quote Originally Posted by DrSmile View Post
    I keep looking for all these rainy day riders in my area... I can never seem to find any.
    Seriously, you've never been caught in the rain? I did a 110 mile NY gran fondo in the rain and descending Bear Mountain was terrifying, even with Mavic Exalith braking. My hands hurt from squeezing the brakes so hard during the 4 miles of switchbacks.

    Disc all the way here. Not sure why we keep having this discussion.

  16. #16
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    thread bump? I love my road discs. I've heated a rim to the point of having a tube burst out. Luckily it was at the bottom of the descent and I was able to stop before the actual explosion. I do have issues with front axle drift, but hopeful that a thru-axle solution will present itself and it becomes a non issue. I've ridden Zipp and Reynolds carbon wheels in the rain and could never brake with confidence, so I second the idea that carbon rims benefit from disc tech.

  17. #17
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    Quote Originally Posted by MoPho View Post
    I am 175-180lbs and do a lot of technical descending with 140mm F/R disc, hasn't been an issue.



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    Big fan of disc and have 140mm on my Domane. I will change them out to 160mm over the winter. Clyde here...BUT it's only to make me happy. Call it a carryover from mtb time. I've had nothing but really good experiences with the stopping power of Ultegra groupset. I do wish there were a little more tight on the pull and less "squishy."

  18. #18
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    I weigh between 130-140lbs depending on season and while 140mm front is adequate, it's a why not situation with 160mm. The added weight is inconsequential and the modulation is better. In the rear, 140mm, hell an imaginary 120mm rotor would probably be enough (though caliper clearance issues would never allow this.)

    Whether your braking fades on descents or not is more due to pad choice than rotor size. I have experienced fade on long technical descents with 160mm rotors and organic/resin pads. I do not experience the same fade with the semi-metallic or sintered pads.

  19. #19
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    While I still stand by my comment that 140mm (as spec'd on my bike) were fine, I did upgrade to 160mm front rotor the other day and there was a significant improvement in braking. I tried metallic pads, and while they were better at first, after a few days they started becoming extremely noisy and I went back to resin.


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  20. #20
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    Quote Originally Posted by carlosflanders View Post
    My view is that anyone on carbon clinchers should be using disc brakes.
    Depends where u live. It's pretty much dead flat in my area, so rim brakes on carbon are perfectly fine. If I lived in hill country I'd use aluminum rims. Disc brakes are just too stupid on a road bike. 99% of people don't get any benefit from carbon wheels anyway less deep dish for aero.

  21. #21
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    Quote Originally Posted by Notvintage View Post
    Depends where u live. It's pretty much dead flat in my area, so rim brakes on carbon are perfectly fine. If I lived in hill country I'd use aluminum rims. Disc brakes are just too stupid on a road bike. 99% of people don't get any benefit from carbon wheels anyway less deep dish for aero.
    psychological benefit of using bling wheelset is enough benefit and motivation to justify carbon wheels

  22. #22
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    Quote Originally Posted by Notvintage View Post
    Depends where u live. It's pretty much dead flat in my area, so rim brakes on carbon are perfectly fine. If I lived in hill country I'd use aluminum rims. Disc brakes are just too stupid on a road bike. 99% of people don't get any benefit from carbon wheels anyway less deep dish for aero.
    The vast majority of people do benefit from carbon wheels, it just isn't the priority target for upgrading. But that's beside the point. The vast majority of riders could benefit from wider tires, and disc brakes allow for wider rims+tires or even different wheel diameters.

    Thankfully in a few years more opinions will change and only true graybeards will consider the inclusion of disc brakes "too stupid on a road bike."

  23. #23
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    Quote Originally Posted by ceugene View Post
    The vast majority of people do benefit from carbon wheels, it just isn't the priority target for upgrading.
    How so?

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