Bottle location and aero

Discuss light weight issues concerning road bikes & parts.
RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

So i am looking at my “round tube” carbon road bike, and my non-aero bottle that goes either on the down tube, or seat tube. To date, i have put my bottle on the downtube for ease of access. I also suppose it looks better.

I have read lots on where to put bottles for the best aero performance. Bars and behind the saddle are off limits.

The downtube seems reasonable given the girth of the carbon there. The seat tube on my felt is far more svelte, but on aero frames, this is usually the prefferable spot of the two. In my case, the seat tube and front derailer would be shielded nicely in the low pressure zone behind a bottle there.

So I think i know the answer, but in a bike like mine, is the seat tube still the preferable location for a bottle vs down tube for aero?

by Weenie


IchDien
Posts: 526
Joined: Mon Nov 05, 2012 12:23 am
Location: Veneto

by IchDien

You might be able to save a watt or two by using something like the B-RAD system https://www.wolftoothcomponents.com/col ... rad-system to move your bottle even lower, if you haven't got extra bosses like some aero frames.

alcatraz
Posts: 2215
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Jersey pocket or behind seat for max aero.

Next is an aero bottle in the triangle.

Obsessing over non-aero bottles in the triangle seems a bit pointless. Wherever they are shielded the most would be better. If downtube is wider than the seat tube then there.

In summer I sometimes wear a drinkbag under the suit. That way I can carry enough liquid without having three cages and three bottles = heavy, unaero. I don't have to reach for anything and I can drink in the aero bars if I need to. 2L possible. I just need to find a way to attach the bag to jersey or back.

If the bag is rated at 2L I wouldn't put more than 1.5L to keep it nice and flat. Shorten the hose, maybe put a thin walled hose there. Swap the bite valve to something convenient. I got an L-shaped one.

User avatar
TonyM
Posts: 3263
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Here the answer (wind tunnel experiment):

https://youtu.be/3eRtGIs7MeE

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

alcatraz wrote:
Sun Jan 13, 2019 12:39 am
Obsessing over non-aero bottles in the triangle seems a bit pointless. Wherever they are shielded the most would be better. If downtube is wider than the seat tube then there.
Pontless? No, there is a difference, even if small. Free watts to shift a bottle position. Why not?

The issue i have is that i have seen conflicting results on seat tube vs downtube being better. Part of the issue is aero vs non aero bottles/frames in the tests.

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

TonyM wrote:
Sun Jan 13, 2019 7:07 am
Here the answer (wind tunnel experiment):

https://youtu.be/3eRtGIs7MeE
Yeah. And then some say the seat tube is faster. But i will give specialized credit in that i am sure they actually tested it... even if they did not give any data on differences/numbers. At least the bottle/bike is somewhat comparable to mine... so i might keep my bottle where it is (also easier to get to).

At the moment i am not interested in a bottle launcher, but for long rides requiring lots of water i might go there. I actually have a couple of back bottles for my pockets, which are pretty comfortable. i just dont like bulky stuff in my pockets, so dont use them much even if i know they are faster. Plus, when i get serious, i am close to, or flat backed, and i figure they help to open my pockets as a nice little parachute... (i know they are too low to do that, and it is still probably the fastest location, but it has crossed my mind)

... and on that note... no wonder a bottle in the back pocket was the most aero in this test. The rider was practically vertical. If you ride around like that, i figure throw aero concerns out the window... cause he is just one big air brake.

TobinHatesYou
Posts: 4195
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Hard for me to believe the seat tube is faster because a cylinder is one of the worst shapes in terms of Cd. On the downtube the horizontal slices of a bottle end up being more oval in addition to being partially obscured by the down tube.

Honestly it probably depends on the bike and how close to the BB shell the bottle is. The closer the bottle is to your legs/feet/cranks chopping through the air, the less it matters. On a traditional steel frame, it's possible the airflow becomes so tubulent past the downtube that a seat tube mounted bottle isn't going to make things significantly worse, but at that point you've already surrendered a ton of watts to having a bike with poor aerodynamic qualities anyway.

alcatraz
Posts: 2215
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

TobinHatesYou is right. The angle will result in a smaller hole for the bottle to cut through. Less frontal area.

If you also change to an aero bottle that doesn't go over the width of the downtube you can probably make the bike faster than having no bottle.

User avatar
TonyM
Posts: 3263
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

RocketRacing wrote:
Sun Jan 13, 2019 8:33 am
TonyM wrote:
Sun Jan 13, 2019 7:07 am
Here the answer (wind tunnel experiment):

https://youtu.be/3eRtGIs7MeE
Yeah. And then some say the seat tube is faster. But i will give specialized credit in that i am sure they actually tested it... even if they did not give any data on differences/numbers. At least the bottle/bike is somewhat comparable to mine... so i might keep my bottle where it is (also easier to get to).

At the moment i am not interested in a bottle launcher, but for long rides requiring lots of water i might go there. I actually have a couple of back bottles for my pockets, which are pretty comfortable. i just dont like bulky stuff in my pockets, so dont use them much even if i know they are faster. Plus, when i get serious, i am close to, or flat backed, and i figure they help to open my pockets as a nice little parachute... (i know they are too low to do that, and it is still probably the fastest location, but it has crossed my mind)

... and on that note... no wonder a bottle in the back pocket was the most aero in this test. The rider was practically vertical. If you ride around like that, i figure throw aero concerns out the window... cause he is just one big air brake.
Actually I was looking for that specific video with all the 3 positions of the bottles but I couldn't find it again...

I mean to remember that the best was in the back of your jersey of course, and then on the diagonal tube and then on the seat tube.
The seat tube was significantly worse than the diagonal tube.
All tests made with regular bottles.

Jere
Posts: 43
Joined: Sun Aug 07, 2011 5:35 am
Location: York Pa

by Jere

RocketRacing wrote:
Sat Jan 12, 2019 11:38 pm
So i am looking at my “round tube” carbon road bike, and my non-aero bottle that goes either on the down tube, or seat tube. To date, i have put my bottle on the downtube for ease of access. I also suppose it looks better.

I have read lots on where to put bottles for the best aero performance. Bars and behind the saddle are off limits.

The downtube seems reasonable given the girth of the carbon there. The seat tube on my felt is far more svelte, but on aero frames, this is usually the prefferable spot of the two. In my case, the seat tube and front derailer would be shielded nicely in the low pressure zone behind a bottle there.

So I think i know the answer, but in a bike like mine, is the seat tube still the preferable location for a bottle vs down tube for aero?


Hi
I know this is not your answer to your question but I had good luck with these bottles last year on my AR Felt

https://www.ebay.com/itm/Two-2-Pack-Eli ... 4d7f67411a

No Aero data but they hold 1000 ML total and are very thin.
JB

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

yeah, those elite aero bottles were top of my list if i went aero bottles. Different designs all seem to have flaws if some sort.

I opted for elite superfly bottles simply for weight reasons. Now that i am adding aero wheels, i am considering other lower hanging aero fruit. Have not allowed myself to swap to heavier aero bottles yet... as my favorite segments are some pretty agressive climbs.

I really need an aero road bike. Then i can focus on pure aero upgrades, and ignore weight. Then my other road bike can focus of pure lightweight... aero be damned. Wife blocked the aero bike however...

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

Double post
Last edited by RocketRacing on Mon Jan 14, 2019 5:32 am, edited 1 time in total.

RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

TobinHatesYou wrote:
Sun Jan 13, 2019 9:07 am
Hard for me to believe the seat tube is faster because a cylinder is one of the worst shapes in terms of Cd. On the downtube the horizontal slices of a bottle end up being more oval in addition to being partially obscured by the down tube.

Honestly it probably depends on the bike and how close to the BB shell the bottle is. The closer the bottle is to your legs/feet/cranks chopping through the air, the less it matters. On a traditional steel frame, it's possible the airflow becomes so tubulent past the downtube that a seat tube mounted bottle isn't going to make things significantly worse, but at that point you've already surrendered a ton of watts to having a bike with poor aerodynamic qualities anyway.
Bottle design and frame design are key. That is why i said round tube carbon frame, and round bottles

Much of the data saying downtube is slower is for aero frames (the tri crowd). In those cases, putting the bottle on the seattube is the lesser of evils, as you don’t want to disturb the airfoil of the downtube. Air is messy by the time it gets to the seat tube anyway, thus the preferable location of the two.

That is why i figured seatube might be faster than downtube for a traditional frame bike. The aero losses of the bottle are not on the leading edge, but rather the trailing edge of low pressure. Fill that with a seat tube and your rear rim, and you have a hack airfoil. Hahaha. Plus, i think my bottle is still wider than my downtube. Messy air flow, and not great for filling the low pressure zone behind the downtube, as the bottle is too wide. As noted above, and aero bottle would be ideal for the downtube, and could perform better than no bottle.

Devil is in the details.

aeroisnteverything
Posts: 193
Joined: Fri Aug 24, 2018 4:43 pm

by aeroisnteverything

RocketRacing wrote:
Mon Jan 14, 2019 5:22 am
yeah, those elite aero bottles were top of my list if i went aero bottles. Different designs all seem to have flaws if some sort.

I opted for elite superfly bottles simply for weight reasons. Now that i am adding aero wheels, i am considering other lower hanging aero fruit. Have not allowed myself to swap to heavier aero bottles yet... as my favorite segments are some pretty agressive climbs.

I really need an aero road bike. Then i can focus on pure aero upgrades, and ignore weight. Then my other road bike can focus of pure lightweight... aero be damned. Wife blocked the aero bike however...
I’ll second the vote for those bottles. Have had those on for over six months now, have not lost them yet, and really have yet to find any downsides other than possibly that capacity may not be enough for hot weather and long distance. Looks super cool too.

by Weenie


RocketRacing
Posts: 886
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

I heard that they dont stay in if you let them collapse, and they rattle when empty.

Post Reply
  • Similar Topics
    Replies
    Views
    Last post