Are aero water bottles worth it? (time & Watts gain)
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Aero water bottles look very fancy on a road bike, even more, when they are fully integrated with the frame or handlebars. We have all seen pros using them on triathlon events. And many wonder if aero bottles are really worth it or if it is just a pro thing.
Using an aero bottle for a triathlon can give you a marginal advantage. It gives up to a 1.5W advantage over standard bottles, which can be useful for long-distance events. This is not the best option to improve your bike aerodynamic and is not allowed for UCI races.
Let’s dig into the details. We will focus on the aerodynamic gains given by aero bottles but also by looking at different options for positioning the water bottles. We will see how much time you can gain and how many watts it can save. I will also review the regulations for triathlon and also for UCI road races about aero bottles. And finally, I will give you my honest opinion about buying aero bottles.
How aerodynamic is a water bottle?
Aero bottles provide to some extent an aerodynamic advantage over a standard water bottle. It is a relatively low advantage, as water bottles being protected by the downtube do not generate much more drag than the frame of the bike.
Aero bottles are water bottles with an aerodynamic shape that can be mounted on the downtube of a bike. Their shape is narrower than a standard water bottle to reduce drag. But this comes with some drawbacks: water capacity is reduced and it is more complicated to grab the bottle and keep it in your hand.
Generally, aero water bottles come with cages that will interface perfectly with the bottle to prevent any gap and space for the air to go through. This makes the bottle more difficult to put back on the cage while riding, increasing the chances of dropping it.
How many watts does an aero water bottle save?
According to this study, an aero water bottle can save 1.6 to 3.9 Watts compared to a normal 500mL water bottle mounted on the downtube. However, the benefits are negligible below 19mph (30km/h). The true benefits only show if you ride at 25mph (40km/h) or above.
In comparison with a 500mL standard bottle fixed on the downtube, the power you have to produce when riding can be reduced. Let’s see a comparison of the watts saved by different solutions for hydration on the bike:
| Rank | Type of bottle | Location | Capacity | Watts saved at 30km/h (19mph) | Watts saved at 40km/h (25mph) |
|---|---|---|---|---|---|
| 1 | Standard bottle | Back of the saddle | 500mL | 1.8W | 4.3W |
| 2 | Aero bottle | Downtube | 440mL | 1.6W | 3.9W |
| 3 | Standard bottle | Between aero bars | 500mL | 1.6W | 3.8W |
| 4 | Specific hydration system(*) | Between aero bars | 750mL | 1.3W | 3.2W |
| 5 | Standard bottle | Back of the saddle | 900mL | 1W | 2.5W |
| 6 | Standard bottle | Seat tube | 500mL | 0.5W | 1.4W |
| 7 | Standard bottle | Downtube | 500mL | 0W | 0W |
| 8 | Standard bottle | Seat tube | 900mL | 0.3W penalty | 0.7W penalty |
in comparison with a standard 500mL bottle fixed on the downtube
The watts saved by different hydration solution depends a lot on your riding speed. The faster you go the more gain you can get from using an aerodynamic solution for hydration. The slower the fewer gains you can get in comparison with a normal water bottle. So before choosing which solution is best for you, start by assessing your average speed on your next race.
But as a general, a standard water bottle mounted at the back of your saddle will give you the best aerodynamic advantage you can get. It is even better than an aero bottle mounted on your downtube.
How much time does an aero water bottle save?
According to the same study, an aero water bottle can save up to 1min30 over the duration of an ironman event (112mi or 180km). You can get the same amount of time-saving by putting a 500mL standard water bottle at the back of your saddle.
In comparison with a 500mL standard bottle fixed on the downtube, you can have the following time gains over the length of an ironman distance:
| Rank | Type of bottle | Location | Capacity | Time gain |
|---|---|---|---|---|
| 1 | Standard bottle | Back of the saddle | 500mL | 1min 45s |
| 2 | Standard bottle | Between aero bars | 750mL | 1min 35s |
| 3 | Aero bottle | Downtube | 440mL | 1min 35s |
| 4 | Specific hydration system(*) | Between aero bars | 500mL | 1min 20s |
| 5 | Standard bottle | Back of the saddle | 900mL | 1min |
| 6 | Standard bottle | Seat tube | 500mL | 35s |
| 7 | Standard bottle | Downtube | 500mL | 0s |
| 8 | Standard bottle | Seat tube | 900mL | 15s penalty!! |
*The hydration system tested in the study is similar to the “Profile Designs Aqualite” drinking system which has been developed specifically for triathletes.
The best solution for aerodynamic gain is a 500mL water bottle mounted at the back of your saddle. An aero bottle comes as an even second place with a standard 500mL water bottle placed between your aero bars. But the aero bottle has a smaller water capacity, which can be an issue on long-distance events.
Are aero bottles UCI legal?
Aero bottles are banned under UCI regulation since 2013. Bottles can only be located inside of the frame: on the down and seat tubes. The dimensions of the bottles are regulated: 4 to 10cm in cross-section and 400mL to 800mL in capacity. Integrated water bottles are also forbidden by the UCI.
UCI races are regulated by strict rules to ensure technology is not coming into the way of the cyclist’s performance. It is important for them to ensure that everyone is riding with a similar aerodynamic advantage. The real function of water bottles is to allow riders to rehydrate while cycling. This is why the UCI considers that using a bottle as an aerodynamic advantage is not fair to the other riders.
“Bottles shall not be integrated to the frame and may only be located on the down and seat tubes on the inside of the frame. The dimensions of the cross sections of a bottle used in competition must not exceed 10 cm or be less than 4 cm and their capacity must be a minimum of 400 ml and a maximum of 800 ml.“
UCI rules – Article 1.3.024 bis
Are aero bottles ITU (World Triathlon) legal?
Aero bottles are allowed under World Triathlon (ex ITU) regulation. The use of aero bottles is not listed in the regulation, meaning you are allowed to use them when racing triathlons.
Should you buy an aero water bottle?
For most people, there is no point in buying an aero bottle. It only provides a marginal gain while making hydration more complicated. It can even prevent you from refilling. If you are a fast cyclist (25mph or 40km/h average speed) it can give the extra gain you need to cross the finish line first!
I do not recommend aero bottled mounted on the downtube for a race. They can be very tricky to get out and back in the cage to drink. There is a risk you might end up dropping it by mistake. I have seen many people complain about this issue. Also, they do not hold much water and you cannot swap the bottle with the ones handed to you at the water stations. So really I don’t think the aerodynamic gain they provide is worth the trouble.
For long-distance events, whatever your fitness level, you can consider putting your water bottle behind your saddle to be a bit more aerodynamic. But don’t do this on race day without having tried it out first! It’s not that easy to grab and put back the water bottle in place from there. It needs a bit of practice!
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