[Paul Donoghue]

Am I the only person out there who is confused by the Body Rocket? I read the piece on Feb 23rd, and have contacted Body Rocket with questions but have had no answers. How do they intend to measure horizontal force with a sensor? They give the equation for calculating CdA- it includes measurement of slope, gravity, and air pressure. Do the sensors measure these or make a guess? Gravity will be pretty easy but not the others. Anyway, if slope is zero and you’re not accelerating, and you estimate air pressure as about 1.25kg/m3, the equation is basically CdA= 2F/1.25x velocity of air squared. Force is measured in Newtons. You get a power meter, so I presume this calculates the force, by dividing the Watts by speed in metres per second. So what are the sensors measuring? It must be wind speed, on three tiny sensors fixed to your bike. How do they do that- with a teeny turbine? Someone please help!! Because it sounds like a con to me.

Topic

[zeeridesbikes]

Well played. 

Well played. 

[Paul Donoghue]

Unsure what your point is
Unsure what your point is here,0-0. Are you poking fun by mimicking me like we used to do in school? I’ll tell my mum.

[0-0]

Am I the only person out
Am I the only person out there who is confused by the new Bugatti Chiron?
I read the piece on Feb 30th, and have contacted Bugatti with questions but have had no answers.
They seem to offer a luxury sports car with exceptional power and speed for so little money.
How do they do that- with a teeny turbine? Someone please help!! Because it sounds like a con to me.

[zeeridesbikes]

Nice little ruse. 

Nice little ruse. 

[Body Rocket]

Hi Paul,

Hi Paul,

Thanks for your question and your interest in Body Rocket. As you’ll know, I’ve replied to the same query that you emailed so here’s the answer for all road.cc followers.

The system measures wind speed, air pressure, temp, etc., which are all required for the calculation of CdA. What separates Body Rocket from all other systems is that we directly measure drag force, like is done in a wind tunnel. This allows us to avoid needing to account for rolling resistance, drive train loss, and changes in body weight, which are the main challenges with which other on-bike CdA systems must deal.

To answer your question about “method”, is this in reference to the virtual elevation testing or the “Chung method” as it’s often referred to? Until our wind tunnel testing in February of 2020, nobody had shown a direct-force measurement built into a bike was possible so there’s not much lingo associated with it yet.  Our measurements boil down to the same equation as a wind tunnel with the addition of a calculation for the slope of the road, as wind tunnels can always assume zero slope.

While a wind tunnel measures drag force in a sensor under the floor of the tunnel itself, we do it by separating the rider from the bike at the handlebar, saddle, and pedals. At those 4 points we’re looking at the horizontal forces. You can think of this as measuring how hard the bike is pushing the rider through the air, which is equal and opposite to how hard the wind it pushing on you (your aerodynamic drag force).

On a flat road at a steady speed this will be 100% your drag force. However, as you go up and down hills a component of that force will also be due to your weight. So we’re also monitoring weight at each point as well as the slope of the hill you’re going up or down. With those measurements we can then calculate the weight component and remove it.

Obviously to get these measurements outside of the wind tunnel we’ve had to exclude the bike from the measurement, but since your body is 80+% of all aerodynamic drag, and the only part that you can influence in real-time, that’s where the real gains can be made.  We do gather power data & so have the same dataset other companies are using to estimate CdA, and we envision having a ‘test mode’ that uses virtual elevation methods to let you test bikes & wheels under controlled conditions.

I hope that gives you a clearer picture of what we’re doing.

Kind regards,

Eric

Founder, Body Rocket

[Author]

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