The Fuel Cell is basically an aerodynamic wash. Very slightly faster at yaw, but basically aerodynamically neutral. So you're really just looking at the penalty for having a waterbottle on the downtube.

" In this test we found that the worst place to keep a 500ml round bottle was one of the more convenient: on the downtube! This cost 5.0w at 40kph, or 2.1w at 30kph. Over an Ironman bike leg at 5hr30min speed (32.7kph) this would be a 2min5sec penalty."
https://www.aero-coach.co.uk/water-bottle-testing

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

So a hair over 1 minute penalty in a 70.3. I just HATE having a bottle in the back of the seat.. Thanks

That's interesting because I saw Lionel Sanders had Gatorade round bottle on his down tube and Sam Long had a flat and slippery Cervelo bottle that comes with P5D on his Argon 18 bike downtube.
Which means Lionel could have had 1 min 2.5 sec penalty.

A lot of pros seem to opt for a downtube bottle (usually aero, but sometimes round), trading off the extra drag for the convenience and ease of staying with their hydration schedules. Having a BTS bottle is a lot less accessible/convenient and also increases the risk of dropping a bottle (stop and retrieve it or get a littering penalty).

https://www.slowtwitch.com/..._Bike_Gear_7546.html

https://www.slowtwitch.com/..._Equipment_7551.html

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Also depending on the bike, what size it is and probably some other factors a round bottle on the down tube can be neutral. I know on my Scott Plasma 3 size M it's been <2w penalty the few separate times I've tested it.

Given that's a bottle I can count on not losing it's a small penalty for increasing the margin of error for a successful race.

Being as aero as possible isn't always the solution for the fastest time from T1 exit to the finish line.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

What is the time cost of a 2W penalty over an IM bike (let's say for an AGer doing 200W for a 5hr split*)? It still might be a couple of minutes, but as you point out there are other tradeoffs.

*Quite similar to: https://www.bestbikesplit.com/demo-race-details

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

I was discussing this with a training buddy yesterday.
The time impact has surely also got to depend on (a) how aero the bike is already, and (b) how aero / what Cda the rider brings to the equation (as that affects how much of a proportion the bike+bottle is over the body).

For me, with a relatively old not-peak-aero bike, and more importantly me being at least 50% bigger than the test rider, waaay bigger chest and shoulder width and, and also me being undoubtedly less flexible and have a less ideal position than she had in the tests, I'd suspect that I'd only be losing circa 1 min on an IM by having 750mm bottles on the down tube and seat tube, compared to 2 bottles BTS. (The delta is about 3 mins using those figures + interpolating the results between the bottle sizes of 500 and 900 for a more regular 750mm bottle we get on course in the UK).

I'm below .210 CdA in race trim...including that downtube bottle.

I also think that if you're CdA is high say > .225 or .230 then trimming some extraneous stuff off the bike may be a wise idea.

On the other hand if you're a rider who overheats or really struggles in hot conditions and/or as you say being 50% bigger than the typical test rider it becomes a balancing act.

Do you add a few watts of drag for more fluid knowing you're also going to be building up more heat if you put out the power to overcome the added drag to get the same bike split as without that fluid. Or do you take the penalty, ride a bit slower so you have more fluids you can bring/drink which may enable you to run more of the run which even if you run an extra mile vs walking it could be a 6-10 min improvement. Running 18/26 miles might yield a 4h marathon. Running 19 or 19.5/26 miles might give you a 3:522 or 3:50. 10 minutes in an IM sounds close yet it's a different zip code

Once you physiologically blow a gasket in an IM you're talking about time increases that are measured in double digits. Now one blows up in an IM, or even a half, and only goes :90 slower. You blow up in an IM and your spending 10,20 and probably more minutes out on the course. In a half it could mean going 5-10 minutes slower.

That's why I've done & do so much testing on various configurations when in the tunnel. So I can answer the if you set it up as A here's the speed difference and the potential consequences. If your bike is set up as B here's the consequences & time savings.

Bringing it back to the Titanflexr's thought is 2w worth going 3-4 min slower in an IM if you can run 10 minutes faster? Now I'm not a genius in math if my D in college algebra is any indication, yet that seems like a worthy trade off to me.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta