This is in response to some of the “critique my position” threads I have read recently…but what is the problem with bottles mounted behind the seat. Isn’t your body in a position that it effectively blocks any air resistance the bottles may create.
On a side note, if I have a spare tube with CO2, is the best spot for this not under the seat?
Aerodynamically it’s debatable.
There have been tests that have had the results lean both ways.
The obvious question is, why would you spend extra for aero tubing, if you are just going to stick water bottles on it? Hense the new Guru and Specialized design.
Personally, I think it very much depends on the frame and the distance of the event.
John Cobb did some wind tunnel testing of various bottle mounting positions and the behind the seat was pretty much the worst. I think it has to do with the air moving around your body and cleanly reconnecting, which reduces drag. The bottles back there upset that reconnection and causes more drag. How significant? Not sure, probably not much.
I miss having his articles up there on bicyclesport.com. Those were very cool.
but what is the problem with bottles mounted behind the seat.
You know I did not have a problem with this until a few weeks ago during a group ride. One of the riders was on a road bike setup with aero bars and bottles/cages behind the seat. Although the guy appeared to be relatively new to the cycling, while in the paceline he was nice enough to stay off the aerobars. Unfortunately along one stretch of road, the surface left a lot to be desired and was very bumpy along with having been recently resurfaced with chip seal. Although riders were calling out obstacles, with me tight on the guys wheel, the rider in question apparently did not see a large bump which results in both bottles getting ‘launched’ from the cages! One was launched with enough force that I actually snatched it out of the air but the other glanced off my calf and hit the ground rolling into the path of my wife who was on my wheel. She was able to avoid the bottle but pandemonium ensured as the remaining riders all started swerving in various directions to avoid the bottle as it rolled/emptied its contents across the road!
Thanks for the link…that is a great summary article.
I saw 2 ejector bottles and one tire pump at Wildflower.
Bottles behind the seat can be rocket launchers. The guys I ride with loss bottles more often than bottles inside the triangle.
I have also seen recent wind tunnel data that showed less drag with a behind the seat bottle holder.
It depends on a range of variables including rider position - in all I don’t think it matters all that much.
You need to carry bottles. Where you put them wont really effect your race time.
Behind the seat bottle holders/launchers do have their purposes - they deter people drafting off you…
Much depends on the type of bottle cages and the type of holders themselves. I have a Minoura mounting system with 2 profile design cages and never launched a bottle once, and I live around some NASTY ass roads. THe ones I see launched (and can’t understand why they are used), are the XLabs. I think the problem there is that the xlabs mount the cage so it is straight up and down so when you hit a bump all the force, sends the bottle straight up. With my Minoura it is angled so when you hit a bump the force is driven into the top of the cage. Hard to explain.
Those Xlabs mount too high in my opinion anyway. It is like having a wall at the back of your bike.
Just my opinion anyway.
I have no choice really. My Aegis Trident can only accomodate one bottle in the triangle. I think most aero frames are like this. So if I want more than 1 bottle for a ride, I need the behind the seat bottle launchers.
The X Labs look pretty pricey too.
FWIW I’m doing my first IM this year and planning on going with a Profile bottle between the tri bars and then having bottle cages as usual - one of which will prob take my spare tyre and tools. Water stations are ample on most (if not all ?) IM courses, so I don’t need a huge capacity.
Why more folks not choose the aerobottles that fit b/w your aerobars like the Profile Design ones…instead of using the behind the seat holders for extra bottles.
I use one bottle mounted in the triangle, along with the areo bottle.
I DO NOT use an arero bottle on training rides, only for racing. Thats just too tri-geeky and will earn you additional scorn from the roadie crowd.
I’m a roadie anyway - and I’d scorn too ! 
There is a world of difference between a 100mile time trial and anIronman bike leg.
I had a training buddy launch a bottle at me, I had seen his bottles rattling around for a few weeks, just waiting for one to come out. We are moving along (~50kph) and come to the base of a climb, I am on his wheel and was planning on going up ahead of him when the climb started to slow us. Just pass the base, I stand up to attack and his bottle comes flying out. No worries, I got my revenge, the bottle hit my foot and ended up hit the back of his leg 
I only have one bottle cage on my P2K, and I cannot race with just one bottle in a HIM (tried at WF and failed miserably). I have a single bottle holder behind my seat, but there is not way to have a bottle come out with a lot of force. The top of the bottle is wedged under my seat. It really abuses the cage because it has to flex a lot for me to get it out. I would like to get an bottle for between my aerobars, just to cheap.
I DO NOT use an arero bottle on training rides, only for racing. Thats just too tri-geeky and will earn you additional scorn from the roadie crowd.
Oh yeah, and I am sooooooo afraid of that happening. What will they do, rub their freshly shaven legs on me or try and suffocate me with their corporate adorned jerseys?
Roadies…bah.
Don’t pee Bettini off or he’ll slam you into the barriers like he did Cooke yesterday!
Personally, I think these things should banned. However, the phenomenon, of the over-the-top popularity of rear-mounted cages and bottles in this sport is rather illustrative of the sheep/lemming mentality that is out there. One guy sees someone else doing something, and pretty soon everyone is doing it, even though it makes no sense, gains no advantage, in some cases actually slows people down and finally makes it unsafe for others.
Rear mounted bottles and cages, despite their popularity:
are of a debateable aerodyanmic advantage
Are hard to access
In the hands of the bad bike handler, make that bad bike handler even worse!
Can irratically and unpredictably launch bottles into the air.
So why use them? It is something I completely don’t understand. Stand at the exit of T1 of any large triathlon partcularly an IM and you will see 75%+ of bikes with rear seat mounted bottles and cages. If there is a curb or a bump to go off, you will see a good percentage of the bottles come flying out right there. It’s a real key-stone-cops type of scene.
I have had the misfortune of being mid bike pack( long story) in a big triathlon recently. I can’t tell you how many people I saw weaving and swerving radically ALL over the road while trying to get at rear mounted bottles. Couple that with the people who did not seem to know how to ride aero-bars in a straight line and, mid-pack in a big triathlon seemed like a pretty scary place to be.
Did I mention that personally, I think these things should be banned.
Fleck