ask and you shall receive

http://forum.slowtwitch.com/...post=4644981#4644981

I think Cervelo pretty much put the kibosh on downtube bottles in their research. Between the bars and then behind the seat, not too wide, is best.

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Thanks. I saw that today also. Great that Cervelo is is doing this research. It would be interesting to see a quantified drag number.

John Cobb found it improved aerodynamics, albeit on a older frame. Still, there's probably something to this. Google slow twitch cobb water bottles to see the old school slotwich article on his findings.

Bigger point (and also raised in the Cervelo article cited) is if it's hot, hydration trumps aero, and having an extra dt cage with an extra bottle is probably going to pay much greater dividends that the few seconds of aero gained. It took me a while to be comfortable with this, but whenever I see the ST Kona pro M and F bike pictures (or the pro bike pictures from a hot Roth or IM Frankfurt last year), I'm struck by the number of very very smart, and aero-concious / well-advised pros choosing to run a dt bottle bottle (in addition to BtA and behind-saddle systems). They know that it has a cost, but find it acceptable, on balance.

I've tested round bottle on the downtube of a lot of bikes. On a few bikes, granted the smallest or near smallest size available the results were interesting bc the bike/rider was actually more aero with the round bottle on the downtube.

On some bikes the medium size bikes showed no penalty with a round down tube bottle and almost universally on the larger sizes a round down tube bottle hurts.

It really depends.
fwiw I don't worry about a round downtube bottle on my bike when I race. The drag penalty for me doesn't impact a number until I get 3 digits right of the decimal.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

Going with both seat tube and down tube water bottles at IMC this year. Smallish tool kit behind the seat. My aero bars are quite close together and I often like crosshanded riding which a BTA bottle does not afford. If it costs me a minute, I'll concede that. If it costs me 3, I'd reconsider.

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http://www.fitspeek.com the Fraser Valley's fitness, wellness, and endurance sports podcast

That's interresting, Brian. Have you tested a round downtube bottle on the IA? I've always thought that I was better off with the aero penalty of the bottle than sitting up fumbling with a rear mounted bottle.

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

For me a XLab aero bottle increased CDa 0.2109 to 0.2207 (can't remember exact numbers this morning but these area pretty close). I did learn racing this past past weekend that I had issues with nutrition and hydration and if I had run the down tube bottle I think it would have solved my problems. My conclusion has been that that aero hit is worth it for me on the keeping down enough food and water. I will make up the difference by running the correct tires :-)

Does anyone have any data on what "aero" bottle on down tube has tested best for them? Or are we assuming that it's a bike/rider specific combo that will differ greatly with each diffreent bike/rider?

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

It seems with modern deep section aero bikes the aero downtube bottles have a lower success rate vs older bikes.

I'd say that it probably will vary some between rider/bike combos

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

Hey Brian if you look at a small bike with a downtube bottle, it is "hidden" behind the fork (from a frontal view) and it "fills in" the frame from a lateral view, so maybe the airflow stays "more laminar" over the entire system. On a larger frame, more discontinuities in the air flow vs the small frames?

A cage? First of all, depends on the cage--a gorilla XT jawn is going to have different drag characteristics than this. Second of all, surely depends on you, your bike/frame etc. Third, it's going to be SO tiny that you might have trouble detecting a difference in testing at all (I know I wouldn't be able to without a wind tunnel).

I personally ditch bottles when I don't need them (when full) more for weight purposes than aerodynamics, but maybe that's foolish I'm not sure--haven't thought about it too much.

When you say you have tested, do you mean with a rider on board? Because the big frame manufacturers have showed that it add ~55 grams of drag, ~25 for an aero bottle.

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I've/we've not run many bike only tests.
I don't pay that much attention to what manufacturers say. We've seen too many instances where they claim X and we see Y,Z,P,A, B and sometimes even X

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Brian Stover USAT LII
Accelerate3 Coaching
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I hear you on not paying attention to manufacturers, and although some of that info is out there in the public, a lot of it comes from private discussions.

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Um, just get a Ventum!!

Considering SdB needed this advice in 2013, I think they've probably moved on by now :-)