Accurate and Repeatable Efforts
The Kinetic fluid resistance power curve is the heart and soul of our fluid-trainer line up. Designed to mirror the resistance of an outdoor ride, our fluid power curve brings the road into your living room. The graph below shows how we can plot power coordinates vs. wheel speed and create a virtual power training experience for Kinetic fluid trainers using the Kinetic inRide Watt Meter.
How Kinetic Power Works
Kinetic Power operates on the principle of speed-sensitive resistance. The accurate power training experience of the Kinetic inRide hinges on the premise that the only factor having any impact on the resistance unit is how fast the roller is spinning; independent of rider weight, cadence, crank length or any other factors.
Using the inRide pod and a magnet in the resistance unit roller, we take speed at the wheel and translate that into power using our formula. The end result is an accurate estimation (+/- 3%) using some very simple and inexpensive hardware.
In Depth: The Science Behind the Power Curve
1. We started by defining the “average rider”
We created an “average rider" assumed to be:
- 165 lbs.
- Riding a 23 lb. bike
- With 170 mm crank arms
- Up a 1% grade
- At sea level
- With no wind
- On rough asphalt
The “outdoor ride” that we reference on the comparison chart above is based on this “average” rider's predicted profile using complex calculations of a variety of forces that interact with all outdoor riders including: rider weight, bike weight, atmospheric density, and other less obvious forces like frontal area.
2. We then calculated how much power it would take for our average rider to maintain a given speed.
3. Next we used Crank Armstrong to measure the power needed to maintain a given speed.
While Crank “road” the Kinetic Road Machine with our Fluid Resistance Unit we altered the viscosity and the amount of silicon solution in the fluid chamber until we matched the data from our “average” rider to the data produced by Crank.
4. The end result is a very accurate power curve and the most realistic indoor simulation.
The Kinetic Fluid Resistance Power Formula
The formula for the Road Machine is a cubic function. If we let S stand for “speed” in miles per hour, and P stand for “power” in watts, the formulas are as follows:
P= (5.244820*S) + (.019168 * S3)
For example, to calculate how much power is produced at a speed of 16.1 mph while riding the Kinetic Road Machine, plug 16.1 in for “S.”
P = (5.244820 * 16.1) + (0.019168 * 16.13)
P = (5.244820 * 16.1) + (0.019168 * (16.1 * 16.1 * 16.1)
P = 84.4416 + 79.9935
Power = 164.435 watts
The Kinetic Road Machine power formula is accurate for all riders because the variables experience on an outdoor ride are controlled indoors.
Limitations of virtual power
While training with speed-based power is affordable and accurate and works amazingly well for longer intervals and overall ride averages, it's not strain-gauge based and does not measure torque, so there are a few things we cannot do. Unlike much more expensive systems, the Kinetic inRide will not register a spike in wattage from a sudden acceleration. The wheel must turn faster before a higher wattage reading is observed, so readings are not instantaneous.
The Kinetic fluid resistance power curve used in the Kinetic inRide will only provide accurate power readings when riding a Kinetic Fluid Trainer. Readings won’t be accurate if used on another brand or with the Kinetic Magnetic and Cyclone trainers.