For most of 2017 and 2018 I rode my white Evo HiMod Disc that I built up with Ultegra Di2. I did my weekly 70km Saturday shopride here in Melbourne, and all the training for Around the Bay, plus doing the event itself. The bike was comfortable for longer rides, and I loved it for my daily Beach Road sprints and charges up & over rolling hills. As that bike was nearing the end of the model year, I sold it (Hi Ross!) and grabbed a simple, mechanical Evo DuraAce with rim brakes (and standard Mod carbon). I thought it was just a holdover until I got a sexy SystemSix, but it was a surprising change and six months on it's not as clear as I thought it would be when someone asks "rim or disc"?
Disc or rim brake?
This is tough and I don't think it can be answered in a definitive one or the other. Answer? it depends. For riders of road bikes, in and around Melbourne, the choice depends on a couple different factors.
The Carbon fork and frame need to be completely re-engineered to make a rim brake bike compatible with disc brakes. The rotational forces that are usually soaked up by the crown of the fork and top of the seatstays on a normal rim brake bike now need to be soaked up nearer the axles, so the carbon fibre layup changes dramatically to meet stiffness and even heat challenges in these normally thin parts of the frame. My impression is that this accounts for the changes in the handling characteristics of the bike while sprinting and turning. Di2 can add a few grams, and disc brakes are a bit heavier than their rim brake cousins. So weight plays a role in this feeling as well. I'm also a mountain biker at heart, so I want to go with disc since that's what I've been riding for twenty plus years.
Yes, the braking itself changes, but for someone that rides mostly flat to rolling terrain, I don't use the brakes much. And as for riding in the wet, I'm not the one who charges out in a rainstorm, I have a Tacx Neo in the garage and am just as comfortable riding on Zwift.
So... When I switched and did the first two rides on the "classic" rim brake Evo, two things jumped out at me:
This thing sprints. When our group was trying to reel in a faster group in front and we only had a hundred meters to close the gap, I felt this bike jump faster. In a situation where I used to give myself a 50/50 chance of holding enough speed to last until I could roll onto the back of the group, I was now 100% confident that the gap was achievable. I tested this feeling over and over and I'm now confident that the acceleration, whether it's the weight or the difference in stiffness, made a difference. Jumping from third wheel to accelerate and win a sprint felt easier. This bike was also 1kg lighter, even though it did not have Himod carbon like the other.
It also climbs better. For the first time ever, I approached the bottom of Oliver's Hill, a short 10percent climb that usually busts up the groups, in by big ring and stayed there up & over the top. The lower weight makes the bike hold it's speed better on those gradients and you can definitely feel it.
But disc brakes brake better! Yep, it's true. When wet, carbon rims with rim brakes are not the best system out there. If you have a wheel that's slightly out of true, advantage disc. If you love speeding into corners and late-braking, and dropping friends on descents, then advantage disc. I also don't know anyone that's delaminated a carbon rim descending on disc brakes; advantage disc. It's said that disc brakes will come down in weight a bit over the next few years as well, so I look forward to this.
Verdict: If you ride consistently all year round and get caught often in the rain, or you have the luxury of nearby climbing rides, the descents are a lot more fun and safe with disc brakes. But they definitely add a bit of weight and change the riding characteristics of the bike a bit. If, like me, you spend a lot of time on flat terrain and don't brake unless there's a red light, then a lighter bike (rim brakes) wins when it matters most.