If I understand correctly, Tilt calibration "zeros" the iBike making it effectively level to the ground. The Calibration Ride generates a "Riding Tilt" that is the amount the iBike tilted (on average) when I ride.
The mathmatical relationship between Aero, Wind Scale, and CdA is clear and obvious. The relationship between Fric, Riding Tilt, and Crr is not so obvious... to me anyway.
If CdA = Aero/Wind Scale, what is the relationship between Fric, Riding Tilt, and Crr?
Thanks
Relationship of Fric, Riding Tilt, and Crr
Re: Relationship of Fric, Riding Tilt, and Crr
crr is an equivalent force to riding uphill all day. So if you have a crr of .006, that is the same resistance as if you were climbing a .6% climb all day.
When you do a coastdown you will get a total friction number, but you need to know how much your stem was flexing to remove that tilt number from the entire friction number. So on the out and back ride you figure out riding tilt, which gets subtracted (I believe) from the total friction with respect to the weight of the rider+bike.
The friction number is the important number for the iBike to have correct, this is the number it uses to compute the frictional component of power. With Gen3, riding tilt is not as important as it used to be because the tilt will correct itself after 5 minutes. But using riding tilt and a known crr, you can back calculate the friction number to get accurate wattage readings for friction forces. This is what the new firmware does when it asked you for a crr before doing your out and back ride.
When you do a coastdown you will get a total friction number, but you need to know how much your stem was flexing to remove that tilt number from the entire friction number. So on the out and back ride you figure out riding tilt, which gets subtracted (I believe) from the total friction with respect to the weight of the rider+bike.
The friction number is the important number for the iBike to have correct, this is the number it uses to compute the frictional component of power. With Gen3, riding tilt is not as important as it used to be because the tilt will correct itself after 5 minutes. But using riding tilt and a known crr, you can back calculate the friction number to get accurate wattage readings for friction forces. This is what the new firmware does when it asked you for a crr before doing your out and back ride.
Boyd Johnson
http://www.boydcycling.com - high performance carbon wheels and accessories
http://www.boydcycling.com - high performance carbon wheels and accessories
Re: Relationship of Fric, Riding Tilt, and Crr
I think Velocomp has not disclosed the relationship. My best guess is that it is something like this:JRB wrote:If CdA = Aero/Wind Scale, what is the relationship between Fric, Riding Tilt, and Crr?
Fric = total weight (kilograms) * acceleration of gravity (9.81 meter/second^2) * (Crr (unitless) - tan(riding tilt (radian))
The tan in the forumla might actually be a sin. Numerically the tan and the sin of a small angle are very nearly equal. So for this application the ambiguity doesn't matter.
It might seem strange that Crr and riding tilt are combined in this equation as they are. If you consider the physics, however, their effect on power scales with weight and gravity exactly the same way. So it actually does make sense to combine them.
Re: Relationship of Fric, Riding Tilt, and Crr
Isn't there a drivetrain loss factor of 2% as well? This could be folded into the friction term, or applied afterwards.