Up to my old tricks again
I guess all this rain is good for the trees and grass but it's grating on me. No matter really today though because today I had the motivation going for any way whatever to put my new/old SRM through its paces.
The first thing I had to do was check the calibration. It only takes about 15 minutes to calibrate an SRM; and everyone has a story about finding a different slope reading from the one SRM calculates during manufacturing or service. I decided it was worth the 15 mnutes' time to check it myself. Besides, if I did come up with a different slope, then I'd have a story of my own to tell.
So here's my story. SRM put a sticker on the back stating their calibration process yielded a slope of 19.2 Hz/N-m. My own process and calculations gave me a slope of 19.59 Hz/N-m. Too bad for me. A higher slope means lower wattage readings. Had I accepted SRM's calibration I'd be a more powerful rider. On paper at least.
The next thing I did was hop on for a ride. I haven't done any steady state sweet spot training in a while so it kind of seemed the natural choice. I broke an hour's training time up into 3x20 intervals and had at it. The first was sort of warming up. The second was a simple sit and spin. The third was my first try at the timetrial position in about a year. It cost me some watts and a lot of discomfort. I didn't really push it because I didn't want to turn my first trial into a test for my back. I just eased on down the stationary road.
Accurate Weight?
Does the weight have to be accurate? Do you use the weight in the calculation? Just wondering if this would have any effect.
Accuracy is important
Yes, it's important to know the weight of your SRM calibration mass as accurately as possible. The weight establishes a non-zero frequency reading for a given amount of torque.
The calibration process uses the zero and non-zero frequency readings corresponding to the zero and non-zero torque values to establish the slope of the Hz/N-m line. If you don't know how much weight you're hanging on the pedal spindles, you can't accurately calculate the torque you're applying to the SRM. If you don't know what torque you're applying you can't calculate the slope accurately.
Both arms?
I found some interesting stuff out with my SRM when I ran the calibration on both arms...I assume you hung the weights on both the drive and non-drive side (at different times of course).
I recall there being a bit of difference between left and right arms with mine...that always bothered me a bit...
all 2 of them
Yes, the calibration protocol I use is to take five zero-offset and five non-zero readings per side. That's a total of 20 numbers: 5 zero readings + 5 loaded readings per side is 10 readings per side. 10 readings x 2 sides gives a total of 20 numbers from which to calculate the slope.
The right side measurements and the left side measurements are always different from each other. I don't know why but they always are. All readings from each side should be clustered closely together. Mine were all within a few Hz of each other per each side.