If you are riding for a long time you will need to ingest fluid and or food at some point if you wish to avoid finding yourself in a very sad place* – or if you wish to maximise your performance. The other aspect to maximising your performance when it comes to fuelling is choosing where to carry your nutrition.
Triathletes are notorious for loading their bikes with all manner of paraphernalia – it should come as no great surprise that all that extra stuff can catch the wind and slow you down. A bit of careful thought can both mitigate risk (of losing your nutrition) and minimise the impact on aero performance from carrying nutrition.
At this point I shall admit my dirty secret – I did my first Ironman carrying four bottles on the bike then wore a fuel belt on the run. My second IM I did for fun (so I carried what I needed to get through), by the third I wore a skinsuit and carried two bottles (admittedly that is not the main reason I went 40mins faster).
With that out of the way let’s consider bottle placement on your bike.
For a long time the prevailing wisdom was based on a John Cobb recommendation to avoid having bottles behind the saddle as the wind would catch them. However, a couple of years ago, the good people at Cervelo released data showing the effect of adding a bottle to several top TT frames. Unsurprisingly the Cervelo P4 (on which the bottle had been designed as part of the frame) showed no detriment.
In the case of the Trek Speed Concept the data showed that a round bottle on the frame would be ~90s slower over an Ironman than a bare frame. And an Arundel aero bottle a bit over 30s slower. Oddly enough, by the time the Kona Ironman rolled around very few of the Trek sponsored athletes were using bottles on their frames (I’m not sure that this is the outcome Cervelo had in mind when they released the data).
This is one of the major advantages for an integrated fluid carrying solution, as seen on the Specialized Shiv. In an article last year I compared the Trek Speed Concept with an aero bottle to the Specialized Shiv (which has a hidden bladder). The aero advantage of the Trek was neutralised. Which means that choosing where you put your $15 bottle cage could be a more significant decision than which $4000+ bike you buy…
On the bright side there has been an explosion in options for aerobar mounted bottles. Cervelo and others (including yours truly) have tested bottles between the arms and found that there is no detriment aerodynamically (and some riders improve their aerodynamics) from shielding a bottle with your hands and arms.
The bike survey at Kona Ironman found that Zip Ties were a very popular method for securing cages to the aerobars. Before the current crop of products hit the market I would fabricate metal/plastic mounts for a secure attachment. Now I tend to use the Profile HC Mount or Aero HC system. You will want to consider both access to the bottle and whether you can still see your computer when you are choosing how to arrange your BTA (between the arms) setup.
Likewise a bottle mounted behind the saddle – if placed correctly the wind will not see it. However this is somewhat individual. As a general rule I try to keep the cage as close to the rider as possible and fairly low (also helps for mount/dismount).
However – at this point we should discuss risk. It’s not for nothing that saddle mounted cages are known as ‘bottle launchers’ – losing your nutrition during an endurance event is what we generally refer to as ‘bad’. So you may choose to combine a BTA bottle (a secure location) with a frame mounted bottle (another trustworthy spot) and accept the aero penalty as a considered tradeoff. If you can find a way to use an aero bottle on the frame you will reduce that penalty (though make sure you have an aero bottle that doesn’t have a tendency to abandon ship).
It would be nice to see a repeat of this testing with new generation frames – the current crop of Cervelos (and a couple of other brands) were designed with bottles in mind so the aero impact of frame bottles has been reduced.
You’re a bit out of luck here. UCI rules specify that the bottle must be placed within the main triangle. So either use an aero bottle (make sure it is of approved dimensions and not mounted too close to the frame) or go without. As mentioned above – current Cervelos are intended to be neutral with an aero bottle so if you need fluid in a TT choose your frame carefully.
Food, glorious food
Cervelo, Trek & Specialized have all tested top tube mounted boxes (‘bento’ boxes) and found that they can beaero neutral. New generation bikes often feature bosses so you can bolt a box directly to the frame (so it doesn’t flop into your knees). Designs like the Torhans Aero Bento make a lot of sense as it is easy to place the box close to the stem – with the aim that it will catch the airflow and smooth it out thanks to the tidy rear profile.
If you’re looking to address all the low hanging fruit – spending a bit of time on working out how to get bottles off your frame (or devise a nutrition plan that allows the use of an aero frame bottle) pays off quite nicely. If you are considering a new bike – think about how you will carry your nutrition – will the aerobars allow you to run a BTA bottle – remember that performance is the result of many factors.
*we call this the “I need chocolate and junk food” state – after an incident where my wife rode for three hours with one bottle of water, not having done much riding in the preceding couple of months. When she messaged me from her glued to the couch position it was clearly necessary to specify chocolate as being separate from junk food for the purpose of restoring her vitality.