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Why choose disc brakes over rim brakes for a road bike?

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Why choose disc brakes over rim brakes for a road bike?

Old 02-20-19, 02:18 PM
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ljsense
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Why choose disc brakes over rim brakes for a road bike?

To me it seems like disc brakes are unnecessary. But they sell so well, so I'm curious why -- why would or did you get road disc brakes? What do you think of them?
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Old 02-20-19, 02:31 PM
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To eliminate wheel rim side wear-through on expensive rims. Conceivably no need for rim brake surface could allow for reduced rotational inertia/mass.

Better performance for someone doing frequent, extended, intense descents with no potential for overheating a tire.

Greater clearance for wide tires assuming frame can accommodate.

But to some extent they are a solution in search of a problem. I have them on one bike, not on the other, and don't much mind either way.
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Old 02-20-19, 02:32 PM
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I bought a bike with disk brakes because they do stop better in rain and slop, which is a frequent condition in Seattle. Rim brakes require a little time to squeeze the water off the rims before they can truly grip.

Other than that one circumstance, my bikes with rim brakes stop just as well. (My rim brakes include Campagnolo NR and SR sidepulls, Mafac Racer centerpulls, R&E cantilevers, a pair of Paul centerpulls, and one set of Weinmann Vainqueur centerpulls. All have Kool Stop pads.)
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Old 02-20-19, 02:34 PM
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If I were doing a lot of riding down mountains in the rain, it might be worth it to me. For my location and riding, totally not.
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Old 02-20-19, 02:40 PM
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My new bike has disc brakes, my old one rim brakes. I got discs so I could easily run wider tires...it was a struggle to get 25's on my rim brake bike. Also love the power of the discs brakes -- they have a lot more stopping power with much less input on the brake lever. Plus the few times I got caught out in the rain it's been damn scary on the old rim brake bike.

But is there anything wrong with rim brakes? Not at all.
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Old 02-20-19, 02:51 PM
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I'm going to try and stick just to your question. "Why choose disc over rim brake for a road bike?"
  1. Disc have slightly better performance in the rain.
  2. You eliminate the risk of resin heat failure on a carbon rim while doing prolonged braking on descents.
  3. Biggest reason - because you have to. The industry has made the decision for you. If you want a new road bike it is becoming increasingly more difficult to buy one that isn't disc.
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Old 02-20-19, 03:02 PM
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Originally Posted by Psimet2001 View Post
I'm going to try and stick just to your question. "Why choose disc over rim brake for a road bike?"
  1. Biggest reason - because you have to. The industry has made the decision for you. If you want a new road bike it is becoming increasingly more difficult to buy one that isn't disc.
Yeah, definitely seems that way. I like disc brakes on my other bikes, but I'm scratching my head here. I mean, I don't think I'll ever want a dropper post on my road bike either, but we'll see where the industry goes.
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Old 02-20-19, 03:02 PM
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I need to swap between 650B and 700C regularly
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Old 02-20-19, 03:20 PM
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So I don't wear my expensive rims out, because they modulate so much better, because it's wet here, to use wider tires, because I don't need rim brakes - do I really want to sacrifice brake quality to save a few hundred grams? Why not only have a front brake for even more weight savings?
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Old 02-20-19, 03:21 PM
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For me, zero need as I live in the desert and don’t ride in the rain. The added weight, complexity and cost make rim brakes a total no-brainer for what I use my bike for.
However, as stated above, my next bike will be disc not because of preference but because I won’t have a choice thanks to the way the market is going.
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Old 02-20-19, 03:24 PM
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Originally Posted by ljsense View Post
why would
They wear the rotor instead of the rim brake track, and a worn rotor is cheaper and easier to replace than a worn rim.

They offer better modulation in wet weather. The rotor is smaller than a rim, so disc brakes are generally designed with higher mechanical advantage and more pad force in order to achieve the same stopping power as a rim brake; this means that there's a lot more pressure between pad and rotor, so muck and water get swept away faster. Brake rotors also allow for more aggressive pad compounds, which further help.

Discs also allow easily changing between wheels of different diameter, although you need to be careful to use functionally-identical hub setups in order for it to be convenient.

No heat buildup at the rim.

And, most of all, rim brake bike selection is rapidly vanishing.

Originally Posted by daoswald View Post
Greater clearance for wide tires assuming frame can accommodate.
This is largely a manufactured problem, though. It's not until you start trying to use tires well over 2" wide that available rim brake tech and standards start getting truly problematic.

Heck, the Deore T610 v-brakes on my gravel bike are a $20 part, weigh about the same as 105-series calipers, fit a tire twice as large, and have comparable if not better power and modulation.

Last edited by HTupolev; 02-20-19 at 03:27 PM.
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Old 02-20-19, 03:28 PM
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Originally Posted by Elvo View Post
I need to swap between 650B and 700C regularly
Sounds more like a gravel/adventure bike than what I had in mind when I said road bike -- but the ability to swap wheels among different bikes if they're all disc braked would be nice, except there are so many different axle standards.
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Old 02-20-19, 03:34 PM
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Originally Posted by daoswald View Post
To eliminate wheel rim side wear-through on expensive rims.
That's really not a legitimate reason.
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Old 02-20-19, 03:38 PM
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Originally Posted by Psimet2001 View Post
Biggest reason - because you have to. The industry has made the decision for you. If you want a new road bike it is becoming increasingly more difficult to buy one that isn't disc.

That's ultimately the correct answer.

I had one gravel bike with hydraulics but have since been sticking with rim brakes. The braking was improved but I hated the bulbous hoods on the bike and hated the aesthetics of the discs. That was one generation ago and things have already improved. As the hoods get closer to mechanical brake size/shape and discs get smaller I won't have much of an argument against them. But for now I ride mostly sunny/dry Southern California on aluminum rims and I'm perfectly happy with rim brakes
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Old 02-20-19, 03:53 PM
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I can't answer for anyone else, but in my case, I really wanted hydraulic disc brakes, because there are many very steep hills where I live (both on and off-road) and I found my hands were fatiguing with conventional rim brakes. After a severe ankle fracture which required surgery and several months on crutches, I also developed a real fear of falling, so there was a bit of a psychological component to this as well. It was at a time when disc brakes were very uncommon on road bikes. Shimano just came out with theirs, and you had to buy Di2 in order to get them, so I really paid through the nose. (I have zero regrets about getting Di2, but that is a different story.) I'm still very heavily dependent upon them, but I've also since found good modern dual-pivot side-pull brakes are pretty good. I don't have carbon rims, and I try to avoid riding in the rain, so neither of those factors really weighed into the decision.

There are still plenty of options for those who don't want them. I think it will be awhile before anyone is forced to use them for road bikes. I think the off-road/adventure/gravel trend has helped to make them more popular for the same reasons that they have almost completely taken over with mountain bikes (including wider tires/rims, modulation and stopping power). Most people who buy bikes have no interest in racing, so the weight penalty unlikely factors into the decision.

I try to avoid DOT fluid versions, however.

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Old 02-20-19, 03:57 PM
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There are regular corners I do -- one is near home, toward the bottom of the hill, and it cuts widely across a divided avenue and ends off camber. It is the final test of many of my rides and my mantra is "practice for the crit, be brave, don't touch the brakes, heavy on the outside pedal, loose through the shoulders." When I'm riding a road bike well, have confidence in my cornering, and am riding in a good group, brakes are pretty much just along for the ride. Bike racing isn't like Moto GP where you accelerate so hard you have to slow way down for the next corner. If anything, it's about finding an extra half pedal stroke so you don't have to accelerate quite so hard after coasting through the corner. Some courses, you don't have the touch the brakes until it's over. That's fundamentally why I don't get why disc brakes are embraced so thoroughly by manufacturers and I assume many buyers. They're not part of anything that promises what to me seems essential to sell a racing bike: you'll go faster.
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Old 02-20-19, 04:07 PM
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Originally Posted by ljsense View Post
To me it seems like disc brakes are unnecessary. But they sell so well, so I'm curious why -- why would or did you get road disc brakes? What do you think of them?
Because like digital photography in film’s heyday, it’s coming, and it’s here, whether you like it or not. You could still ride rim brakes (like you can still shoot film), but they’ll be less common until they slowly disappear. Just IMO, IME (photography). Once sales from disc brakes die out the industry will find new ways to *encourage* you to *upgrade*. And on and on....
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Old 02-20-19, 04:08 PM
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Originally Posted by wgscott View Post
I can't answer for anyone else, but in my case, I really wanted hydraulic disc brakes, because there are many very steep hills where I live (both on and off-road) and I found my hands were fatiguing with conventional rim brakes. After a severe ankle fracture which required surgery and several months on crutches, I also developed a real fear of falling, so there was a bit of a psychological component to this as well. It was at a time when disc brakes were very uncommon on road bikes. Shimano just came out with theirs, and you had to buy Di2 in order to get them, so I really paid through the nose. (I have zero regrets about getting Di2, but that is a different story.) I'm still very heavily dependent upon them, but I've also since found good modern dual-pivot side-pull brakes are pretty good. I don't have carbon rims, and I try to avoid riding in the rain, so neither of those factors really weighed into the decision.

There are still plenty of options for those who don't want them. I think it will be awhile before anyone is forced to use them for road bikes. I think the off-road/adventure/gravel trend has helped to make them more popular for the same reasons that they have almost completely taken over with mountain bikes (including wider tires/rims, modulation and stopping power). Most people who buy bikes have no interest in racing, so the weight penalty unlikely factors into the decision.

I try to avoid DOT fluid versions, however.
That all makes sense to me.
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Old 02-20-19, 04:11 PM
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I just looked at the current listings for Trek Emonda.

14 different ones have discs
12 different ones do not

For Domane, discs are a bit more dominant, but most of the moderately-priced ones have both options.
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Old 02-20-19, 04:13 PM
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Originally Posted by Seattle Forrest View Post
because I don't need rim brakes
This is the best reason.

Rim brakes simply aren't necessary.


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Old 02-20-19, 04:14 PM
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Originally Posted by rubiksoval View Post
That's really not a legitimate reason.
It can be if you're riding in mucky conditions.
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Old 02-20-19, 04:15 PM
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I regularly ride a CX bike with bike bottom-of-the-line Shimano hydro discs and a road bike with DA 7800 brakes and Ksyrium Elites. Both systems are meticulously maintained. The rim brakes are simpler, prettier, and lighter, and work fine, but there is just no comparison on braking power and modulation. I especially like the added safety margin the hydros give me in traffic.
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Old 02-20-19, 04:18 PM
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Originally Posted by ljsense View Post
Some courses, you don't have the touch the brakes until it's over. That's fundamentally why I don't get why disc brakes are embraced so thoroughly by manufacturers and I assume many buyers. They're not part of anything that promises what to me seems essential to sell a racing bike: you'll go faster.
I don't ride anywhere like that. Coming down a hill, somebody could pull out of a side street or driveway at any moment, or a kid or dog could run out into the road from between two parked cars.
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Old 02-20-19, 04:20 PM
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Originally Posted by MoAlpha View Post
I regularly ride a CX bike with bike bottom-of-the-line Shimano hydro discs and a road bike with DA 7800 brakes and Ksyrium Elites. Both systems are meticulously maintained. The rim brakes are simpler, prettier, and lighter, and work fine, but there is just no comparison on braking power and modulation. I especially like the added safety margin the hydros give me in traffic.
Yeah, that's a good point -- probably a big part of it: a customer goes into a bike shop, test rides a couple bikes, and one thing that will stand out even in a cruise around the parking lot or the local streets is the stopping power and feel of discs.
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Old 02-20-19, 05:23 PM
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Borrow one of your Classic and Vintage buddy's beloved bikes with steel rims and try to brake when the rims are wet. You'll think rim brakes on aluminum rims are the greatest thing since sliced bread.

Disc brakes offer pros the ability to brake very late into a turn or curve and to do it with confidence. As though Sagan needed any help. :-)

Disc brakes allow us mere mortals a large margin of error for when to brake and how much to brake. I don't really care to push the envelope much when carving S-curves on a big descent. Feathering my rim brakes at such times can be tricky lest I overdo it. But not braking enough may require me to either crash into the ditch or use the other lane; not a fun option even with the view is clear.

So I anticipate the situation and slow down earlier so that I don't force myself into bad decisions. My next bike will probably have disc brakes but in the meantime I'm using common sense with my rim brakes.
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