Aero claim buster

June 28, 2011

Consumers often complain they can’t verify aero claims made by manufacturers. True, unless you have a windtunnel in your backyard.

But you can use the laws of probability and common sense to set the minimum level by which a bike manufacturer would lie about its models’ aerodynamics. Here is now:

  • Bike manufacturers make claims on weight and on aerodynamics.
  • The first you can verify, the second you can not.
  • I would say they will AT BEST their aero claims will be as honest as their weight claims. Probably the aero claims will be even less honest.

Makes sense, doesn’t it? If they lie 10% about a claim you can verify, do you really expect them to lie less about a claim you can’t check? So get out those scales and go weigh some aerodynamics!

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25 Responses to “Aero claim buster”


  1. Hmm, good point. As a mere mortal, for me personally when I upgrade my current road bike, weight is far more attractive than aerodynamics. I think I would gain more in getting an R3SL as apposed to a S3.


    • Thanks for the reply. You would “get more” out of a lighter bike than an aero bike how? Certainly not in speed, those 200g on a total of you and the bike combined doesn’t amount to very much. The aero vs weight tech presentation on http://www.cervelo.com gives some interesting info on that.

  2. Lance Says:

    Lets not start on claims for comfort as well !

  3. Darren Hague Says:

    Verfifiable claims are great, Gerard – but the “lightest aero frame in the world” (http://www.cervelo.com/en_us/bikes/2011/S3/prices-specs/) doesn’t seem to make a claim for its weight. What are we to make of this?

    That said, in the first race on my new S1 last week I scored my first ever points and was passing folks even as I crossed the finish line, so I don’t doubt the aero claims. :-)

  4. Kev Says:

    Its even more comical when looking through a rival manufacturers catalogue, where the bikes are weighed usually 54-55cm models, without bottle cage or pedals fitted.
    Pointless.

    I am all for progress of design, useability & versatility of bicycles, but I sometimes feel the frame weight emphasis overcomes common sense.
    Cervelo’s R5CA is a design example of what can be achieved, especially that Hushovd can ride it and he is no lightweight, but sadly they remain one of a select few.


    • Well, I am not sure quoting a size 54/55 is so bad, it’s better than an unpainted size 43! In fairness to bike companies, differences can occur depending on if things like seattube collars, water bottle screws, etc are part of the frame weight or not, so I’m ok with a few percent off. But when a company’s weights are 10, 20 or 30% off, I’d put zero trust in their aero claims.

  5. Lance Says:

    When I`m offered the choice at Brainbike I take an S3 , everytime .

  6. raymond Says:

    That’s why Giant was smart enough not to post bike weights. Let the consumer weigh the bike themselves, and eliminate dissatisfaction from innacurate claims.


  7. We have developed an on-bike wind sensor that measures airspeed and yaw. The associated software computes CxA vs yaw.

    This will enable coaches to honestly assess real-world aerodynamics. Very soon, you won’t need to extrapolate honesty by using a weigh scale.

    Andy Froncioni
    Alphamantis Technologies
    Montreal, Canada


    • Hi Andy,

      I don’t mind you plugging your product on my blog (within reason), but I don’t see how measuring this will enable you to measure bike performance to within 10 or 20%. It would be a great training tool for sure, but with 10% variance on the bike drag being the same order of magnitude as 2% of the rider drag, it would be tough to measure what was the bike and what was the rider. No?


      • Thank you for indulging me, Gerard.

        Is “bike performance” really that aerodynamically separable from the whole rider/bike combination? For each different frame, after all, there is a subtle (and unique) change in rider position that optimizes drag. Measuring the frame aerodynamics alone is like listening to the sound of one hand clapping.

        Extremely subtle CxA differences have been detected using virtual elevation. Winners have been made using this method.


  8. Agreed, some claims on aero and weight are a bit optimistic.

    One problem is the test protocol, there are many variables here, even in a windtunnel. Rider or no rider or dummy, pedaling or not, what position, what wheels, what parts, test velocity, yaw sweep, etc. Every one has a different opinion on how to test and tunnels are not directly comparable.
    So it is difficult to categorically say one bike is the absolute best for someone, especially when the bike was tested without a rider, or when only CFD “diagrams” is presented.

    Often the windtunnel is used a photo studio, which can be quite funny when the brochure shows things that don’t really make sense.

    At least with the scales there are only small variations in the earths gravity!

  9. Matt Says:

    GV, thank you for validing my argument regarding aero and the consumer.

  10. Rowan Says:

    This reminds me of something I read somewhere (can’t remember where, sorry) about optimising aero set-up on the cheap. It needs a hill, three friends, a stop-watch, the bike you are optimising, another bike, and some time.

    Friend 1 and you roll across a mark at the top of the hill at a fixed speed (say 25km/h) together, and keep rolling to the bottom of the hill. Friend 2, who is at that mark, waves his hand, then Friend 3, who is at the bottom of the hill, starts a stopwatch, and then notes when each of you cross the line.

    Next, you start making changes to one bike only, and repeating the process. Gains or losses are seen in a change in the relative times. The second bike is the control, and accounts for changing wind conditions, someone pouring treacle on the road etc.

    There is no reason you couldn’t do the same with the whole bike, especially if you used one wheelset to eliminate changes in rolling resistance. Of course, you would need the manufacturer to lend you their frame for a while…


    • Hi Rowan, absolutely, coast-down tests are used regularly by people. It won’t allow you to optimize small details, but big chunks like the choice of frame, wheel or aero helmet can definitely be researched this way. Provided you can create fairly constant conditions (wind, traffic, etc).

  11. Tom Anhalt Says:

    Gerard, my main problem with the concept you outline is that it may tend to further reinforce “weight weenie-ism”…or the irrational importance put upon weight in regards to performance.

    We need to promote “Aero weenie-ism” instead! Nothing that some quality time with a power meter, a low wind course, and an Excel spreadsheet (or Aerolab in Golden Cheetah) can’t handle ;-)


    • Hi Tom, I certainly don’t want to promote weight-weenie-ism, it causes a really terrible rash. Of course I am only suggesting to weigh the frame, I don’t care about the number that comes out – only the delta to what was promised.

      And maybe the opposite would happen, companies would stop lying about the frame weights, and therefore stress weight less and consumers would also obsess less about it? One can dream.

  12. Ryan O'Hara Says:

    The issue I am having with my s1, size 48 (considering the possibility of getting an s2 or r3. see weight vs aero argument described above) is that by the time I put 2 water bottles into the frame I’ve drastically changed the characteristics of the trailing edge of the down tube, and leading edge of the seat tube. Prior to having the the water bottles added there would have been minimal pressure drag from flow separation (mostly frictional… but minimal at that) but now with these 2 big water bottles the laminar flow over the foil will be interrupted introducing pressure drag behind the bottles etc. Also with a crosswind I have effectively created a “solid area” (sail) that pushes me around to no end (of course being a smaller rider I don’t weight more than 125lbs). I suspect these issues are not as pronounced on bigger frames. I guess my concern is that I feel once my 48 aero bike is “set up” some of the aero characteristics I bought it for may be lost….? Thoughts?

    • Darren Hague Says:

      Hi Ryan,

      I addressed this problem on my S1 by using a Specialized aero bottle & cage on the downtube. One bottle is plenty for the 1-2 hour races and club TTs that I do, and for training (where aero doesn’t really matter) it’s easy enough to put a couple of normal bottle cages on instead.

      Cheers,
      Darren


    • Thanks for the feedback. Although the effect of the bottles is not as big as one would think, it is definitely a factor. Which is why th new S5 has been designed specifically for bottles, with separate optimization for one or two bottles, round or aero. They spent a ton of time on the bottle optimization, I think there is some data that will be presented on that soon.


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