What's more aero?

I am having a debate with some colleges about this situation in relation to what is more aerodynamic in a gravel race.

The concept is say you only need to consume 20-23oz of fluids an hour and your nutrition plan is liquid within that 20-23oz.

The debate we are having is it more aero to carry a 50oz racing water pack or is it more aero to carry 2 bottles on frame?

For the debate lets just say the race is a short distance 2hr race and the pack in debate is say this;

What does the TR forum say and why?

This might be worth a watch:

Been a while since I watched it, so it might not hit your specific examples though.

As to bottle aero questions, a ton depends on the bike in question. Some are actually faster with bottles than without.

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I’m tempted to say that carrying the two bottles behind you like this would be more aero than the pack.

But who knows how this would hold up in a wind tunnel?



Great point!

Thank you for the video!

Lets use my bike as an example, a Ridley Kanzo Fast with 45mm dept wheels that are 40mm OD and 30mm ID utilizing 35 tires that blow out to 40.

I would call the bike a complete aero package

Does the pack prevent cooling


What rims have 30 ID?

I have two USWE packs (Outlander and Ranger) and though I race XC/XCM so the bottle aero isn’t as big a thing, I suspect that the pack is more aero. If you were really committed you could wear it under your aero jersey.

The biggest advantage I have is being able to swap the bladder out. Aid stations (with drop bags) take me about 30seconds and that’s the only stop for my long racing.

I just raced our state gravel championships and used only the bladder of a camel bak inside the rear area of my speed suit. I find the backpack holder is too bulky.

I also do a similar setup on endurance tt bike rides.



That is an interesting idea. Does the bladder stay in place or does it shift around?

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I’d expect the pack to be more aero. As Chad noted though it’d vary bike to bike.

Also drinking from it is likely to be more aerodynamic than reaching down to a bottle cage. Your forearm is a cylinder (ish) that will be close to perpendicular to the wind while you’re reaching for the cage. That’s not a great aerodynamic profile. Whether that matters depends how often you’re drinking.

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I’d say it’s a wash in a gravel race, at least the longer ones.

Bottles don’t have that much drag to begin with, especially when you’re riding in a group.

As the field splinters, you might see an improvement with the pack, but that’s also when the temperatures start climbing and the heat can destroy your sustainable power. And your speed goes down so even less drag.

Then there are races like Unbound where you might need to carry the bottles AND the pack…

I had no problems with it shifting. On the gravel bike I used it in the rear but On my tt bike i place it in the front.

It holds about 2-3 bottles worth of fluid. I just feed the tube over my shoulder and tuck it in when not being used. #aeroAF


Here’s an article about bottle positions, that don’t answer your specific questions but will still probably be of interest.

As for the vest, I don’t believe an exposed hydration pack will ever be faster than your bottles. Aero gains (admittedly when clean, which isn’t the case at the end of a gravel race) for skinsuits is claimed as over 30w between a bad skinsuit and a good skinsuit. Correct material, seams and trip line positions being a focus, it’s hard to see how a small backpack with a tube sticking out wouldn’t have a decent aero penalty.

Having it under a skinsuit ( similar to Julich or Schleck) would be a good discussion, as thatd be a purely it depends situation that you wouldn’t know without testing. If you can potentially waste a skinsuit on stretching it, I would stick it down the front with some ice if it would give a cooling effect, and help fill out the unaero “void” under your chest when you ride low.

I’d guess this as well. Something I’d be worried about with the water pack is additional heat if racing in the summer. You also have to factor in how easy your containers are to fill up at rest stops. For a 100% self-supported race, you can’t swap bottles or bladders.

I’m curious how the Crank Tank performs. Less weight than both per amount of water hauled.

On long gravel events the trend is to have the bike carry the weight not the body

See Colin Strickland 2021 unbound set up and Dylan Johnson did something similar

“Comfort is speed.”

Shorts with a bladder pouch :stuck_out_tongue_winking_eye::call_me_hand:

That sounds like it takes 28 seconds longer than swapping bottles out?

I think bottles are unquestionably faster aero wise, and ease of exchanges. Some courses are better for bladders if they cause you to stop less, or the course is technical enough that finding spots to ride with one hand and get your nutrition is tough.

A slim fitting pack under your jersey vs bottles might be interesting aero wise.

Or putting your back on your front, under your jersey…like you’re a kangaroo. Haven’t tried that to see how uncomfortable it is though.

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I stop once instead of four times. Not usually full bottles at each aid station. Only at the bag-drop.

Plus, it’s massively easier for me to hydrate with a bladder than bottle.

This looks great for winter ultras, actually.

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