Do the Dome?
I started writing this as a technical document but let’s face it. I should be doing other things and so should you so I will write this more as an abstract.
Over the course of the last 4 years I have been to many test facilities including A2, CMEFE, and done multiple velodrome tests regarding dome top bottles. I tested multiple bottles between the arms (BTA), down tube, seat tube, and with multiple behind the saddle single & double mounts.
When the standard bottle is BTA it is in turbulent air and essentially a free nutritional storage place without an increase in drag. When adding a dome top bottle facing forward there is negligible difference when compared to a standard bottle, but when the bottle is facing rearward (dome toward the saddle) the drag was slightly lower than a forward facing dome shape bottle. Now the differences talked about above were consistent but very very small, we’re talking fractions of a Watt yet this explains why there is a business for BTA systems.
On the down tube the dome top bottle is a case by case basis.
I have tested it on the old Ordu and gotten the dome top bottle to be faster, on the new Ordu the dome top bottle is slower. So this one isn’t even worth researching because it is so frame specific, so unless you do testing on a velodrome or wind tunnel…your guess is as good as mine!
On the seat tube I have the least amount of data since most TT frames don’t have seat tube bottles anymore. What I did find was the dome top bottle was slower than a flat top bottle regardless of the height of the bottle (20, 24, or 32 oz) which surprised me.
Then came the behind the saddle mount the dome top bottles were the same if not slower.
I did not find any cases where the bottles were faster. This was the only location of all of them that I tested over the years where the loss versus a flat bottle was significant enough to use the word Watts. The bottles actually act as a spoiler and reduce the turbulence created by your enormous thighs.
My takeaways. The biggest take away is the bottle cage has a greater effect on your overall drag then the bottle in the cage. Some of the nicest cages on the market just kill you in drag while some of the cheapest simplest cages I have found to be really fast. Are dome top bottles worth it? Yes, dome top bottles are worth the investment only if you have a bottle arrangement BTA and down tube so the bottles are interchangeable. If this is not your plan I would use the good old schooled flat top bottles.
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