Hi I recently bought a SRM pro and also have a std powertap. After installing the SRM on the bike I took it out for a quick ride and I see that the power readings are lower with the SRM (~5%). I've read posts about calibration of the SRM by hanging a known mass off the crank, but my question is can I get a close approximation by comparing the SRM data to the powertap data (from an interval recorded in parallel) and then using the SRM software to adjust the slope post ride to match the power produced with the powertap?
That assumes the one sample of PowerTap is 100% accurate.
It does make it easier to compare data files to do what you are saying - I just calibrate the SRM with weights and check the PowerTaps every once in a while and have to deal with the slightly different data when I compare rides.
You can download a file into the SRM software and play with different slope values.
I'll probably keep both powermeters on the bike for a few rides and see how they compare with some longer rides. Kind of off topic but if the power sensor gives me a stable zero offset and its between 300 and 800 can I assume it's installed correctly? does it have to be absolutely parallel to the back of the crank for accuracy?
