The Win Tunnel: Which is More Aero? Rim Brakes or Disc Brakes?

Well, when it to their commercial benefit, companies will claim an 8 second disadvantage in 40K is nothing. When their product gives an 8-second advantage they will claim it’s HUGE.

@Dave B: exactly. Imagine if they found that the Evade was 8 seconds faster than the Air Attack. Holy Moses, would :08/40K be an AMAZING time savings.

As for the cross vs. headwind: I don’t know how many times I’ve ever ridden into a 0-degree headwind. Maybe like 3 in my entire 30+ years of cycling. Normal wind conditions are almost always at some degree of yaw. Virtually identical in a 0-degree headwind is pretty well meaningless for real world application.

What about the weight penalty? When you have multiple corners in a descent, it usually implies you have to go up another hill. What would the extra weight would add to you time going uphill? Considering the costs and the very small potential gain (demonstrated loss on flat land), I will keep my rim brakes…

There are a couple of problems here:

First and foremost, no one really makes disc-specific aero rims. Disc specific rims don’t need a brake track, which could have significantly implications for rim shape and for general aerodynamics.

Aong with that, you have rim weight. If you don’t have a brake track, you can further reduce weight. Which would move weight away from the rim, and towards the hub.

And, total weight, as far as I can tell, is not an issue. You can build a 6.8kg disc-equipped bike pretty easily with modern components. With the previously mentioned changes to bike design (rim shape and weight), you could end up with a disc-equipped bike that is actually more aerodynamic, at the same weight, with less rotating mass.

S needs to get this kid to wind test eating gels vs bars. gotta help as many stravatards as possible.

ok but which electronic contraption is perched on a stravatard’s bar is more aero? garmin or iphone?

Andy… I wonder how much of what you’re saying would make a significant difference. Devil’s advocate here – I don’t know the real answers of course… Does a current Zipp (for example) brake track shape vary much from the aero ideal in the first place? I don’t think you have to modify the cross section of a brake track much for braking purposes to make it work well for aero purposes, and the surfaces don’t have to be precisely parallel for braking anyways. I think Zipp did some sort of “caulking strip” at one point to fill the tire/rim gap (which could be done for disc or rim brakes), but I think that starts to get impractical, or annoying pretty quickly (and adds grams again).

How much weight does a carbon tubular brake track really add, especially when you figure it’s gotta have some impact resistance anyways (at least for cross use or pothole crack prevention), and the fact that a disc up front adds torque at the hub that means a spoke pattern and strength that wouldn’t be needed in a rim brake.

Finally, 6.8 kg UCI rule may soon be gone. If so it would be easier to get a bike down to, say, 5kg w/ rim brakes for a Pantani-sized climber and aero would again have to be balanced against weight.

… and apparently I missed the VN article that just came out and addressed a few of these issues. All interesting stuff, especially the yaw angle differences that make a crosswind from one side insignificant, but pretty huge from the other side. I guess we’ll see which way the industry heads over the next few years with this, thru axle, hydro, electronic and everything else. Back to my fixie.

Cam is SO dreamy!

People, discs stop better in all conditions. This is safer and allow you to ride more confidently. For all but a very very few of us the slight aero and weight differences are inconsequential. I know, change is hard–When I started MTB in 88 I loved my Canti’s. I resisted switch to v-brakes for too long. Same from V to disc. I was wrong. If you can swing it, upgrade to disc on the road, ride forward, and don’t look back. Rim brakes will not be around on performance bikes within a handful of years. This is for the same reason drum brakes are not used in cars anymore–because they don’t work as well.

And I use a fixed gear…no brakes to slow me down (or stop me) and no derailleurs to get in the wind. I get home 5 minutes faster with this setup. 😉

For extreme aero using wire spokes one can go 12 spokes min rim braked. Prob 24 spokes is min dished. If the wheel acts like a fan less blades is more aero. Then with discs bigger is better. 140mm on the back is a tad small. How about 160mm? How big could one go, 200mm? Nah , let’s go really big. Why not integrate the disc into the surface of the rim? Yeah big discs are best (aka rim brakes).

From someone who owns a 15 S-Works Tarmac Disc and has real world experience with it, the felt aero difference is negligible compared with my 13 Tarmac. This is right in line with VeloNews and Specialized testing.

Braking is altogether different. It is VASTLY improved. Since I live in the mountains and love the technical descents, I’ll take the disc over rim brake any day of the week. Coming from a motorsports background, a lackluster braking system is the first thing to get upgraded on a car. There’s nothing like confidence inspiring brakes.

The entire peloton WILL be on hydraulic disc brakes in the coming years. It’s just a matter of when, not if.

When everyone rides the same brake system, then 8 seconds does not matter in wheel to wheel racing.

iTT racing is different.