In the wind tunnel: Disc vs Rim Brakes

In this episode of “In the win tunnel” Chris and Cameron of Specialized answer the question of what the aerodynamic differences are between rim and disc brakes. It’s not as much as you might have thought…

mzungu

Funny…. , I like their marketing spin…. when they try to sell you a new bike, they say they spend the whole year to shave that 8 seconds off from last years model, Now, they try to sell yu a new system, it’s like that 8 second really don’t matter in the big picture. :P I suppose they save something for them to work on next year.. and shave another 8 seconds off something…
PieterVP

Mike Hed said that disks doubled the drag on a front wheel.

Tour magazine was quite unimpressed with the performance of disk brakes during Alpine descents (various brands, rotors melted, fade).

They also add about 600g to a bike. Weight loss at the rim is minimal.

Finally, have you ever tried to change a wheel with disks in a hurry? When you add the rule about lawyer tabs on the forks it becomes a total faff.

I can’t help thinking that disk brakes are a ploy to get people to buy a new bike. After all … that’s Specialized’s ultimate goal. They have the perfect cover of ‘increased safety’.
- Timmeh2015
  
  Mike head is wrong. There is newer data than this that proves it.
  
  Discs do NOT add 600g. Check your math.
  
  Rims will be 30~60g lighter EACH. Please check ENVE.
  
  The market for discs is not currently the RR crowd. The best application is GF riders.
  - PieterVP
    
    Hi Tim,
    These are my calculations:
    1) Frames that are adapted for disk brakes are about 100g heavier than standard frames.
    
    2) There is a 500g difference between Shimano BR-R785 disk brakes and Shimano Ultegra standard calipers. If comparing with Dura-Ace it is 600+g.
    
    3) ENVE SES 3.4 ~30g per rim lighter than standard 3.4 rims.
    
    100 + 600 - 2 * 30 = 640g
    
    Regarding aero data - I’ve seen the Specialized report, which surely can’t be regarded as independent. Mike HED’s not around anymore to back up his claim, but the question is easily settled by someone with a wind tunnel and a couple of bikes (to be continued).
    
    Regardless, look at the amount of time and effort put into handlebar design for aero gains, then compare that to plonking a load of hardware on the front fork.
    
    Agree, discs are probably great for GF (Fondo?) riders. Reduces rim wear, work well in the wet, they don’t have to worry about spares or wheel changes.
    
    But for now, if trying to go as quickly as possible, rim brakes seem to be the best choice.