# Training & Nutrition - Kaiser M3 and true wattage

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View Full Version : Kaiser M3 and true wattage

Hezz
03-11-09, 12:14 AM
Lately it seems to me that my stationary bike is not really cutting it and I would like something that simulates a real bike better. I don't have room for a trainer inside since the setup is too long for the room it's in and for various other reasons I like a stationary bike. I have been using a Lifecycle magnetic trainer. THe only problem is that I can't ride out of the seat because it's highest setting isn't hard enough and the non adjustable handlebar position makes it even more difficult.

It also has the same problem that almost all stationary bikes have. The resistance does not increase with the speed like with a real bike. The only stationary bike that I have seen that can do this is the Kaiser M3.

At the Innercycle forum there is a long discussion on the wattage readouts on the Kaiser vs. a CycleOPs power tap. Does anyone have experience with the Kaiser. There seems to be the notion that the power meter on a bike will be more accurate because it is calibrated to the cyclist. But I have good reason to believe that this is not the case.

It's true that a power meter on a bike needs to be calibrated to the rider. That is because the riders weight effects the force being moved since the bike is moving through space. And will vary when going up a hill since gravity becomes involved as a force. But on a stationary bike this is not the case. The only things that effect the wattage are the moving parts friction, the weight of the flywheel which is constant, the strength of the magnetic resistance, and the distance of that resistance from the flywheels center of rotation. Since the rider is not moving through space his mass will not effect the wattage calculation very much. Though, I assume the weight of his/her legs will have some small effect on the total calculation. All the variables on the stationary bike are knowns that can be measured once at the factory. And calibrated at the factory. So the Kaiser should be rider independent and it's wattage should be even more accurate than a bike power meter which varies a little bit due to road undulations.

Any cycling engineers out there that can verify this?

NoRacer
03-11-09, 06:55 AM
The only PM that has to be calibrated to a rider is the iBike.

Strain guage based PMs are calibrated to a specific amount of force on the strain guages. Weight (rider and bike), gravity, wind resistance, and rolling resistance doesn't need to be known in this type of system. The only thing that needs to be known is that if I place a certain amount of force on the strain guages, the correct amount is displayed on the computer in terms of watts (the actual calibration may use torque).

gregf83
03-11-09, 11:19 AM
According to the manufacturer the Kaiser M3 is not calibrated and they make no claims about the accuracy of their power estimates. The best you could hope for is that it remained consistent over time. It shouldn't stop you from getting a good workout though.

I agree with NoRacer that power meters don't need to know your weight.

Hezz
03-11-09, 11:22 AM
Thanks, Noracer. This is interesting information. It also makes sense. It looks to me like the only calibration on the bike PM is to dial the computer into the strain gage's tolerance variation using some kind of known reference. It still seems to me that the method used on the Kaiser, though perhaps not as accurate, would still be very close. Using more a mathematical approach to calculate the wattage, it still would be quite accurate since there are few unknowns in the calculation. Assuming that engineering and manufacturing were done correctly.

gregf83
03-11-09, 11:55 AM
Here's a quote from a Keiser Rep on how they calculate power taken from another forum (http://www.innercycling.com/f/showthread.php?t=8542&page=2):

"John,
First and foremost the M3 is not a ergometer nor is it priced like one. Power is an estimate. The price and our maximum usage (group exercise) dictate that it is not for testing and it cannot be calibrated. Though we do have some people that have used it with an IMET test when a bike is more preferential than a treadmill. One thing not mentioned below is magnet strength, they are consistent and do not weaken over the life of the bike.

Watts are calculated from the gear setting. A potentiometer is attached to the magnet holder (the round cone shaped disc at the end of the shifter cable). As the shifter is moved, the cable rotates the magnet holder. A potentiometer is rotated by the rotation of the magnet holder, thus feeding information to the computer on the position of the magnet holder. The rotation of the potentiometer is broken down into 24 gear settings. A dynamometer was used to test and develop a table of wattage at various gear settings and speeds. The speed of the crank is determined by a magnet attached to the large pulley on the right crank arm and a magnetic switch attached to the circuit board in the magnet holder assembly. Each time the magnet on the pulley passes by the magnetic switch, a signal is sent to the computer to compute the RPM's of the crank arm. Power equals force times velocity. The force is determined by the magnet position and the speed by the crank speed. The lookup table is programmed into the computer and the computer simply looks at the gear setting and speed and goes to the lookup table to find and display the Watts for those two settings.
Darrin Pelkey
VP Sales & Marketing at Keiser
The Power in Human Performance"

Hezz
03-11-09, 06:00 PM
Thanks Greg83,

Good information. I am going to study it further.

Terex
03-18-09, 08:57 PM
I really like the M3's that our gym just purchased. But, I've found that there is a fair range in resistance in individual gears. If wattage is calculated just by, say, "Gear 11", you can wiggle the "11" setting so it is more or less resistant. Again, I really like the bike. MUCH better than the Schwinn's that were there before.

First night we had them, there was a fair amount of fiddling around to get the feel of the unit. I averaged 186 watts. Second night, not as much fiddling, and I averaged 226. Third time I used it, I snuck in for a solo recovery spin after a weekend of outdoor riding. I got into a nice, easy grove, looked down, and my cadence was right at 90. Neat.

I think I will have a problem NOT trying to up my average wattage most times I ride the bike. :)

I'm already thinking about 1) doing a wattage ramp test, and 2) seeing if I can sustain 330 watt for 30 min.