How should you mount your rear bottle holder?

Where is it most aerodynamic to put your rear bottle holder? I was curious about this and asked my sponsors at StacZero if they could help me answer this using the virtual wind tunnel. After having scanned my position at Sykkeltilpasning in Drøbak outside Oslo they had a virtual figure of me on my QuintanaRoo in the aero position. With that, we could play around. This is what we found out:

Baseline – No rear bottle holder – CdA: 0,185 – Time difference 180km: NA
Adding another aero bottle on the frame – CdA: 0,186 – Time difference 180km at 250watt: +36 seconds
Having a rear bottle at this position – CdA: 0,188 – Time difference 180km at 250watt: +76 seconds
Having a rear bottle in this position – – CdA: 0,184 – Time difference 180km at 250watt: -14 seconds
Having two rear bottles at this position – CdA: 0,185 – Time difference 180km at 250watt: +6 seconds
Having two rear bottles with a wider gap – CdA: 0,185 – Time difference 180km at 250watt: +6 seconds
Having two bottles behind and another in front of the saddle – CdA: 0,185 – Time difference 180km at 250watt: +6 seconds
Having two rear bottles at this position – CdA: 0,185 – Time difference 180km at 250watt: +9 seconds

 

While all there numbers seem fairly similar we should have a closer look at how this could be more than marginal differences.

We decrease our aerodynamic performance from baseline with another aero bottle on the downtube by 36 seconds, which we carry with us in all the other setups. Looking closer at position C and D we find a substantial difference.

This rear bottle adds 76 seconds compared to baseline which with the rear bottle causes 40 seconds of that (36 was the down tube bottle)
A rear bottle in this position reduces the time with 14 seconds compared to baseline, which adds up to 50 seconds if removing the down tube aero bottle. Compared to position C it saves you 90 seconds(!), which at least in my book is huge when thinking of the seemingly minor difference.
The calculations above are based on a flat course, but BestBikeSplit predicts that a 2 % reduction in drag makes me ride 1 minute and 25 sec faster. For «average Joe» it would be more.

Where you should put your water bottle, of course, depends on several factors. How many bottles do you need? And do you have a strong enough bottle holder to keep them in place at position D? For that case the Xlab Gorilla XT is my recommendation.

My general advice would be:
  • Only use an aero bottle on the frame, and preferably on the seat tube
  • Have a bottle in a rear bottle holder as much as position (not C as I first mistakenly wrote) as possible, even if you are not planning to actually use it
  • Having a regular bottle between the arms is the best solution in terms of practical use and aerodynamics.

And last, train on your setup and makes sure it can handle bumpy roads.

Publisert av

triallan

I am a 33 year old PRO triatlete. My goal is to swim, bike and run as fast as possible, and enjoy the journey. All my adventures and triathlon related stuff is well documented on this blog.

3 kommentarer til “How should you mount your rear bottle holder?

  1. The point about the bumpy roads cannot be stressed enough. I have had many bottle/cage combinations failed me before.

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