CarloM

Talk about a can of worms!

Here's a nutshell of the arguments, and full disclosure, I have discs on all of my bikes so I definitely have a bias/preference.

• In general, historically, disc specific frames weigh more than rim brake frames. This is starting to change, as manufacturers have gotten better at creating road bike disc frames because it's the way of the future. Take Canyon's new Ultimate CF EVO, the rim brake is 6.00kg and the disc version is 5.99kg. I would say starting with current frames and going forward, the weight issue will be largely a non-issue save for those who will really be able to tell a 30-50g difference.
• In general, historically, it was said that disc brakes are less aero. But like the weight issue, manufacturers are now making shapes that incorporate the disc concept into the overall aero design and some makers are starting to claim that their disc bikes are "as aero" or even "slightly more aero" than their rim counterparts. Again, for 99.5% of us riders, we won't tell the difference between 1-2 watts of aero savings or cost.
• For those who prefer rim brakes, they say "they stop just as well" as disc, or "they're good enough and have been for many years". To me that second one's not a good argument, because fixies were good enough for many years. Then 10 speed. Then 11 speed. The big ring/small ring. Etc. Time marches on and technology progresses. Here's something I have yet to hear (with proof) "rim brakes stop better than disc brakes".
• It's generally acknowledged that disc brakes perform better in wet weather/less than ideal conditions.
• It's generally acknowledged that if you are into expensive carbon wheels, having rim tracks on those expensive wheels will wear them down/out. And rim tracks on carbon wheels and wet weather = dicey braking.
• At worst, disc brakes and rim brakes stop "equally" in good conditions. Although personally when I've tested rim brake bikes (on expensive models), I've preferred the feel of disc brakes. Admittedly that's personal preference. Go out and try both yourself and see how they feel. At best, many acknowledge that disc brakes can be superior even in the best of conditions, although this margin of improvement is smaller compared to inclement weather conditions, where the margin grows much wider.
• Disc brakes require more complex maintenance. True. You never have to bleed rim brakes. I've only been cycling on discs for 5 months so I haven't had to bleed any of my systems. Some say brakes should be bled every 1-2 years (with regards to DOT oil systems like SRAM). Others say many more years, unless you introduce air into the system, for mineral oil systems like Shimano (i.e 5 years?). I think the jury's still out on this.
• Disc braking systems also have different feel. I happen to own Tektro 160s (Trek), Shimano Ultegra (TCR) and SRAM eTap HRD (Cervelo) and all 3 feel different. The Shimano has the most progressive feel, like a car brake, first half squeeze is only a small percent of the power, and then progressively over the last half of the brake lever travel the brake power ramps up. The SRAM is most "bite-y". It doesn't take much to engage the full stopping power of the brake. The Tektro is in between, but closer to the SRAM than the Shimano in feel. All are hydraulic systems. I've never ridden a mechanical disc brake system.
• Cost of parts maintenance is cheaper on rim than disc. Partially true. If you have a good aluminum wheel you like, then replacement parts for rim brakes is basically the pads. That costs less than pads for disc systems and disc rotors. Although rotors last a very long time and aren't that expensive, I have seen the Dura-Ace rotors on sale for around $50 each and unless you're really using your brakes a ton I don't see rotor replacement happening annually, likely less frequently...maybe much less frequently. The story changes for rim brakes if you use carbon wheels. Because once the brake track wears down on carbon wheels...that's an expensive replacement upgrade. Granted it doesn't happen often, but if let's say you get 8 years from a great set of Zipps or ENVEs...that's still $2500 divided by 8 years = $312 per year. That's more than if you were to replace two Dura Ace rotors and pads annually over that same span of time by a factor of 3X. Now granted you can justify it by saying you're getting new wheels too. So it's all up to you and your perspective on these kinds of things.

Also forgot to add the rotor rub issue. My TCR has been fairly flawless with rotor rub, but the S3 was problematic and finicky from the beginning. I had chalked it up to tolerance issues, Hambini will tell you that SRAM tolerances are......not a word I would use in polite company. But it turns out that the RAP axle has largely addressed that issue. So to me, rotor rub and alignment is something that you can avoid with proper set up. Your LBS should do this upon your purchase, but there are also tons of helpful videos online from GCN, Parktool, etc. If you're even halfway handy with Allen wrenches it's an easy job to align brakes.

I realize I hadn't made a recommendation. My recommendation is to go with hydraulic disc brakes because the industry is going that way. Current frames will have largely mitigated or eliminated their weight and aero drawbacks. No one has ever said that disc brakes stopped worse than rim. And to me safety is paramount. Hopefully you'll never need the improved braking power in inclement weather...but when you do, you'll be glad you have it.

I understood the arguments 2-3 years ago when discs were just going mainstream in road bikes (though they've been on MTBs for much longer) and the frames were optimized for rim. But for any 2018-19 frame onward it really makes sense to me to go with disc.