Downtube aerdynamics question

pianoman
pianoman Posts: 706
edited November 2010 in Road beginners
I saw a Giant TCR bike in a shop the other day and think it absolutely looks the dog's b******s. But It seemingly had quite a wide downtube compared to narrow designs found on TT bikes.

Apparently this means you'd lose a few seconds over 25 miles, right? Well, surely having a standard bottle and cage on a narrow-downtubed bike would completely obliterate all the benefits? Wouldn't the wide bottle cause less aero disturbance on a slightly wider downtube? And wouldn't the thicker tubes mean more stiffness?

Unless of course I buy one of the Specialized "4 pint milk" style bottle and cage sets that is.........

Comments

  • dennisn
    dennisn Posts: 10,601
    I think you're making way, way more of this than the actual reality of things. If you really like the looks of the bike, then get it. If you don't you'll most likely sort of regret it. As for a few seconds one way or the other, I doubt anyone, and I mean anyone, could prove much of anything along the lines that you ask about. Not worth even considering. Get the bike you want, and the one that fits you. Not some bike that simply claims to be faster. They all claim that.
  • Bar Shaker
    Bar Shaker Posts: 2,313
    The front wheel and its spoke will ruin any aero properties of the down tube, even with deep carbon rims.
    Boardman Elite SLR 9.2S
    Boardman FS Pro
  • pianoman
    pianoman Posts: 706
    So the downtube is essentially irrelevant when it comes to aerodynamics then? Interesting that this particular Giant doesn't have either round tubes or narrow ones; it looks like a square "box-section" when you look at the downtube from above. Not unlike some of the wide but straight-laced nosecones seen on the 2010 F1 cars really.

    BTW has anyone ever tried out these aero bottles? I think they're quite cool really! And you could even put a sponsor name or club logo on it :idea:
  • cougie
    cougie Posts: 22,512
    Unless you're planning on going in a wind tunnel to absolutely optimise your aero position - you're fretting over nothing.

    Aero bottles are pants in my opinion. Over priced, hard to come by and restricting. Round are cheaper, plentiful and lets you use all of your bottles. You'd never see a difference in performance using the aero over the un aero one...
  • Monty Dog
    Monty Dog Posts: 20,614
    Most of the data published regarding the benefits/advantages of an aero frame are bollox because most of the testing is done without a rider - the arms, head, shoulders and flailing legs of a rider do more to disturb the airflow that any aero-downtube can alleviate. Whilst the marketing folks might see this as an important USP and invest heavily in advertising to promote the point, in the real world what makes the different is an effective position and sustainable power of the rider - you only have to go down to your local club 10 to see people struggling to break 25mins on Cervelo P3 with Zipp Wheels and yet it's perfectly feasibly to ride a 22 on an old steel frame with drop bars and traditional wheels ....Just buy the bike that fits you best and prefer the look of - that should give you enough motivation to get out there and ride.
    Make mine an Italian, with Campagnolo on the side..
  • pianoman
    pianoman Posts: 706
    I think, more to the point, it's nearly impossible to have a test ride on some of these aero "frames" simply because shops aren't going to build them up at great expense only for them to sit there for months unsold.

    As someone who regularly finds regular jerseys flap around even when small sizes (meaning I'm not very aerodynamically efficent anyway), methinks I could save hundreds by buying a standard-tubed frame ready-built with Campag e.g. Wilier La Triestina or one of the basic Bianchi bikes (good looking bikes DO go faster, trust me, you feel GOOD) :wink: Then I could get a skinsuit and even have a couple of hundred left over :idea:
  • lae
    lae Posts: 555
    Yeah I'd agree that aerodynamics, although interesting, aren't particularly important so long as you aren't timetrialling at a professional level. Drop bars and a racing tuck will give you the most noticeable aerodynamic benefit and all road bikes have that!

    It's not helpful to think of the aerodynamics of a road bike in comparison to an F1 car - the aerodynamics of a bicycle are designed around top speed, whereas those of an F1 car are designed around downforce and cornering ability (all those wings and bits limit the top speed of an F1 car massively - a normal road car is three or four times more 'efficient' in terms of top speed than an F1 car is!)

    If you're interested, Bicycling Science is a good book which has a chapter on aerodynamics.

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