I've had a new SRM D/A compact powermeter on my bike for about a month now, and I just want to verify that the zero offset behavior I'm seeing is normal. After a month of riding, everything SHOULD be pretty well bedded in. During the course of a ride, the offset bounces anywhere from about 510 - 545. Today's ride was a good example. I usually put the bike outside for about 15 minutes before my ride. It registered 525 when I jumped on to begin the ride. Every 30-60 minutes I would check it again, and it was never the same value as the previous take. At the one hour mark it was 540, after two hours it was 515, at three hours 530, etc. There was no major temperature fluctuation, and it seems to jump up AND down during the course of a ride. Does everyone experience this? Just how much would this affect wattage? Sorry if this is a repost, but I couldn't find any reference to this exact situation when I did a search.
I've had a new SRM D/A compact powermeter on my bike for about a month now, and I just want to verify that the zero offset behavior I'm seeing is normal. After a month of riding, everything SHOULD be pretty well bedded in. During the course of a ride, the offset bounces anywhere from about 510 - 545. Today's ride was a good example. I usually put the bike outside for about 15 minutes before my ride. It registered 525 when I jumped on to begin the ride. Every 30-60 minutes I would check it again, and it was never the same value as the previous take. At the one hour mark it was 540, after two hours it was 515, at three hours 530, etc. There was no major temperature fluctuation, and it seems to jump up AND down during the course of a ride. Does everyone experience this? Just how much would this affect wattage? Sorry if this is a repost, but I couldn't find any reference to this exact situation when I did a search.
Dave
yeah, no worries, its typical behavior. if you always measure from the same spot (i.e. crank arm at 45 degrees) then the offset will yield more similiar results.
you can also go into the SRM software and your "homepage" you will see a button to the right labeled properties. Once you're there it will bring up a box and one line has the offset for your ride, you can change it to see how much of a difference an offset of 510 compared to 540 makes. hope that made sense.
I've had a new SRM D/A compact powermeter on my bike for about a month now, and I just want to verify that the zero offset behavior I'm seeing is normal. After a month of riding, everything SHOULD be pretty well bedded in. During the course of a ride, the offset bounces anywhere from about 510 - 545. Today's ride was a good example. I usually put the bike outside for about 15 minutes before my ride. It registered 525 when I jumped on to begin the ride. Every 30-60 minutes I would check it again, and it was never the same value as the previous take. At the one hour mark it was 540, after two hours it was 515, at three hours 530, etc. There was no major temperature fluctuation, and it seems to jump up AND down during the course of a ride. Does everyone experience this? Just how much would this affect wattage? Sorry if this is a repost, but I couldn't find any reference to this exact situation when I did a search.
Dave
Make certain that 1) the sensor is close enough to the crank - if it isn't, the zero offsset will flucuate significantly (i.e., more than 1-2 Hz) depending on crank position, and 2) that you aren't inadvertantly putting any pressure on the pedals when checking the zero offset (the easiest way to do this is by unclipping entirely).
Thanks for the quick response. I just moved the sensor as close to the crank as I could (only about 1-2mm closer than before, though) and will be sure to always check the offset at the same crank location. Hopefully that will help stabilize things. Even though it's only a few watts difference between these offset values, those few watts are critical when doing L4 workouts. People keep giving me funny looks out here because I spend half the time on downhills with both feet unclipped fiddling around with the PCV!
Thanks for the quick response. I just moved the sensor as close to the crank as I could (only about 1-2mm closer than before, though) and will be sure to always check the offset at the same crank location. Hopefully that will help stabilize things. Even though it's only a few watts difference between these offset values, those few watts are critical when doing L4 workouts. People keep giving me funny looks out here because I spend half the time on downhills with both feet unclipped fiddling around with the PCV!
Dave
Two other things that I forgot to mention: 1) make certain that all of the fasteners (e.g., chainring bolts) are torqued to spec, and 2) allow the zero offset to 'settle' for a little while before setting it. The latter makes a bit of a difference because residual strain after a hard effort can briefly elevate the zero offset. Thus, if you reset it too quickly, you very well could get a lower number later, and will just end up 'chasing your tail' trying to get a stable value.
