Disc brakes for road bikes might be a controversial topic but a short ride on Shimano’s new R785 disc brake group has reinforced my belief that it’s inevitable (Sram recall notwithstanding). The variable is if the industry goes quickly and willingly or kicking and screaming. The group is being competition tested now in cyclocross by Nys, Albert, and Walsleben.

Here’s the lever. This is a Di2-only group – there’s no shift mechanism inside the hood, so it can stay relatively svelte despite housing the reservoir. It’s not the prettiest lever ever, or even the second prettiest, but the ergonomics are spot on.

You tend to brake longer and more consistently on the road than mtb or cx, so cooling is critical. The rotor is a steel-aluminum-steel sandwich that takes advantage of aluminum’s superior heat conductivity (just like All Clad cookware!). More aluminum extends toward the hub with a scalloped profile to increase surface area. The pad holders also have aluminum fins to dissipate heat. This technology is carried over from Shimano’s downhill Saint components. Total heat reduction is claimed to be 200 degrees. These are dual piston calipers that, if properly set up, don’t drag on the rotors at all.

The four arm spider for the rotor is unique to the road group. 140mm rotors are standard for front and rear and provide more than enough stopping power, with no rider weight limit. The hose for the hydraulics is a little less stiff than its mtb counterpart. Its ability to expand in volume slightly gives the system more modulation – kinda like how brake cable housing compresses a little. 

A non metallic resin pad comes standard for the group. It’s supposed to be less prone to squealing though less long lasting. On my test ride it was perfectly silent, and so smooth there was no sensation of a rotor grinding past brake pads (it’s not impervious to squeals if you get it dirty, however). The smoothness is slightly eerie and totally awesome. The smooth and quiet operation gives you confidence to carry more speed and brake later and later.

Ultegra Di2 gets a nice upgrade. Both derailleurs are slimmer, with new motors and graphics. The rear derailleur has a couple of cage options so you can run crazy wide cassettes like an 11-32. This is an Ultegra group but it’s compatible with Dura Ace Di2 derailleurs and XTR calipers if you want to drop some weight.

The Ultegra crankset is now four armed like Dura Ace. With the same crankset you can run 53-39, 52-38, 52-36, 50-34, and 46-36. Yep, you can get a 34-32 low gear. 

This Colnago has an internal battery, so this installation is doubly clean. There’s no cables or housing on the bike, it’s all wires or hydraulics. I especially like how clean the upper half of the bike looks without cables and brakes.

Downsides

Ok, let’s dump some cold water on this.

It’s heavier by up to a pound or so. A true apples to apples weight penalty is around 340 grams, but since a high end wheelset with a superlight rim doesn’t exist yet, there isn’t a true apples to apples comparison in real life.

Forks and stays will have to be stronger and heavier to withstand braking forces. Frames are heavier now but Specialized think they can make purpose built disc frames lighter than rim brake frames. Wheel options will be limited at first, and rim weight won’t drop that much even though braking surfaces will be eliminated. You can’t have exotic super low spoke count front wheels, and at the very least the brake side spokes will have to be crossed.

This is a first generation product, so there will be kinks to work out. Shimano’s hoping the industry will adopt the system, opening up frame and wheel options. Rear spacing is 135mm, so that’s another new standard to embrace. And until wheelmakers jump in, you’ll be the owner of a sick sick bike with just ok wheels.

Road discs are not UCI legal, so the initial market for this will be gran fondo riders, CX racers, and riders who live where they climb and descend a lot. And if it does become legal, gradual adoption in the pro ranks would be mayhem. Can you imagine a guy on carbon wheels with rim brakes following a guy on disc brakes down a descent, finding out too late that the disc brake guy was going to brake really late and hard before a switchback?

Conclusion

Better brakes make you safer (duh) but the real advantage is how much faster you can bomb descents when you trust your stopping power, and how much more control you’ll have on great modulating brakes that feather nicely with minimal effort. For now the only option for a road bike is the Colnago, with Cannondale possibly coming next. It’ll be interesting to see if discs become ubiquitous on the road as they have in mtb.