I am a Quintana Roo ambassador and sponsored by their Norwegian retailer JBS Sport. QR have both disc and rim brake triathlon bikes in their entry-level and high-end bikes. 

As a technical solution for reducing the speed of your bike disc brakes are superior rim brakes. They have a much higher braking power, better modulation and do not lose their performance in wet weather, which is especially true for carbon rims. Just ask an MTB rider if he or she would ever wanting to go back to rim brakes.

Why road cycling has used such a long time to follow has only one valid reason; they are very traditional and like things to be as it has always been. Triathletes are different in that way and have always been early adopters and pioneers regarding equipment. Why are we so late to the disc brake party?

Why not have disc brakes on your triathlon bike?

1. It increases aerodynamic drag– I had a talk with Chris Boardman in 2016 were I expressed my wish for disc brake. His argument against it was clear; A disc brake increases the need for stiffness in the wheels which typically adds 4 spokes on the front wheel. That increases the aerodynamic drag. I have no data how much the increase from 20 to 24 spokes on the front wheel will add. I cannot believe its much, but it has to be something. Note that Quintana Roo, in their own testing, found the disc to be more aerodynamic in nearly every yaw angle due to the design.
2. It increases weight– As of now, the typically added weight is about 200 – 300g on a disc brake vs rim. For me in Norseman that would translate into 18 – 27 seconds.
3. You don’t need the increased braking performance – In most triathlons, the bike course has a very low technical difficulty, with little need of good braking power. In Ironman Hawaii you basically have two turns and only need to brake a third time when getting your bike at T2.

Why should you have disc brakes on your triathlon bike?

1. It has superb braking power– While you don’t need very good brakes at most triathlon races, there are certainly a lot of races where you do. Norseman is one of them, Ironman Wales is another and Patagonman among those races where you either really love your disc brakes or wished you had them.
2. It has superb braking power – Racing is not the only time the performance of the bike is important. When training I often ride more technical roads than in races and often in wet weather. Disc brakes enable me to ride safer and faster in training, which I can transfer into better and faster riding in racing.
3. It has superb braking power – Most of the time you are riding you don’t need brakes, but when you need them, you need them. And sometimes, if example a car don’t see you are coming and drives out right in front of you, you REALLY need them. Good brakes can mean the difference between crashing and not crashing.
4. Easier to adjust and maintain – Everyone who had a triathlon bike with hidden brakes knows it can be a hassle to adjust and maintain. Especially if you switch between racing wheels and training wheels with carbon rim and alloy rim with different width. Disc brakes enable you to switch between a racing wheel and training wheel much quicker, especially if you got hubs with identical width.
5. Increases the lifespan of your wheels – The brake surface on a carbon rim is limited. Yes, it lasts roughly 20 – 40 000 km, which is a few years of cycling, but it gets worn. On a wheel with disc brakes, the rim last forever.
6. Increased stiffness – Thru axle increases the stiffness of the wheel making energy wasted on pushing the wheels sideways becoming slightly lower.

Weighing the pros and cons against each other I opted for the disc brakes. While not being the similar obvious choice that it is for MTB and road bikes I am certain that it is the future. I have no doubt that the weight gap is going to become lower and that the aerodynamic performance of disc brakes will outperform rim brakes in a few years. Disc brakes enable much more variations in bike/fork design which increases the likelihood of decreasing drag. I will go so far to say that there will not be sold a new high-end triathlon bike with rim brakes after 2020. I may, of course, be wrong, but we will soon find out.

Despite only using disc brake for one race and a few training rides before the race I am very confident that I made the right choice. The braking performance is just so much better and makes the fast technical downhills so much less scary and does not keep me worried if it is going to rain or not. The tire grip is, of course, the limiting factor, but with good width and correct pressure, it’s far better than you think. With the improved braking modulation it is far easier to find the sweet spot between braking enough and locking the wheel. As a triathlete, I have joined the MTB riders regarding the disc vs rim brake debate. I will never go back.