ljsense

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?

daoswald

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.

Aubergine 

caloso

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.

JasonD67

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.

Psimet2001 

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.

ljsense

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.

Elvo

I need to swap between 650B and 700C regularly

Seattle Forrest

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?

BluFalconActual

HTupolev

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.

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.

ljsense

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.

rubiksoval

That's really not a legitimate reason.

rms13

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

Cyclist0108

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.

ljsense

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.

GreenAnvil

ljsense

That all makes sense to me.

Cyclist0108

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.

TimothyH

This is the best reason.

Rim brakes simply aren't necessary.


-Tim-

HTupolev

It can be if you're riding in mucky conditions.

MoAlpha

Seattle Forrest

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.

ljsense

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.

bbattle

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.