4iiii left crank power meter readings

mjh892

Just brought my first power meter a 4iiii having never ridden with one before. Fitted and calibrated as per instructions. Did an FTP test. Power readings covered a vast area from approx 50 to 350 but it gave me an ftp of 187. On a ride this morning with my garmin set at 3s avg there was no way I could train using the power meter as reading were fluctuating greatly from under 100 to well over 250 even when on a steady road in hr zone 2. Is this common with power meters or is it likely mine is at fault? If normal how can i use it to train within my zones? Thanks

super_davo

If you're on a slightly rolling road it's highly unlikely you'll be outputting a constant wattage unless you're specifically trying to. Especially at a fairly low effort level like zone 2 (HR lags way behind power). So I wouldn't automatically assume your PM is at fault.
It could be; the way I would rule that out is by sticking it on the turbo and trying to keep to a steady speed and seeing how the power stabilises. It will still go up and down, but it should do much less, and it should be apparent if there are wild swings.

PM pacing and training is a complex thing and many books have been written on the subject. My advice is whilst you're new to a PM to just ride as you did before and look at your power figures after the ride. Look for things like what's your average power, is it improving since your last ride, how much higher is your normalised power than your average. If there is a big difference, that suggests you could benefit from better pacing; there are many books and far more qualified people than me to tell you how to do that.

peteco

Power on the road does fluctuate significantly - this is a consequence of the many parameters affecting your pedalling on the road. It is smoother on a turbo. I have a 4iiii single crank power meter, and a Powertap crank based one - they both behave this way.

Pete

captain_chaos

On my Garmin I show the 10s average power which is a reasonable trade off between showing change and stability

StillGoing

mjh892 wrote:

Just brought my first power meter a 4iiii having never ridden with one before. Fitted and calibrated as per instructions. Did an FTP test. Power readings covered a vast area from approx 50 to 350 but it gave me an ftp of 187. On a ride this morning with my garmin set at 3s avg there was no way I could train using the power meter as reading were fluctuating greatly from under 100 to well over 250 even when on a steady road in hr zone 2. Is this common with power meters or is it likely mine is at fault? If normal how can i use it to train within my zones? Thanks

I'd move to 5s or even 10s average until you're used to pacing within a power zone. If you find you're holding within the zone, you can then begin reducing it down to lesser averages. However, trying to hold specific watts is harder than trying to stay within a zone when you take the rolling undulations, wind and traffic into account.

sloppyschleckonds

If you're training with power why are you using HR

foggymike

I use 3s average on my display so it responds fairly quickly to efforts - I 'd be more likely to think there was a problem if it didn't keep changing.

As you get used to having it and what different zones feel like you'll probably stop looking at it quite so often or for so long and won't notice the changing so much

supermurph09

mjh892 wrote:

Just brought my first power meter a 4iiii having never ridden with one before. Fitted and calibrated as per instructions. Did an FTP test. Power readings covered a vast area from approx 50 to 350 but it gave me an ftp of 187. On a ride this morning with my garmin set at 3s avg there was no way I could train using the power meter as reading were fluctuating greatly from under 100 to well over 250 even when on a steady road in hr zone 2. Is this common with power meters or is it likely mine is at fault? If normal how can i use it to train within my zones? Thanks

That's part of why you have zones, it's extremely difficult (impossible even on the road) to stay at X wattage. So let's say you're wanting to do an hour at "L2", that wattage range will be about 50 watts as the top and bottom ends are based on a % of your FTP. You should be able to keep it within that range without too much trouble (you may need to think about your route) so when you come back home and look at time spent in that zone it should be well over 85% if you've ridden constantly for that time.

The best thing to do with a new PM is to keep riding for a few weeks and get used to the fluctuations. For a test to ensure it's working then putting the bike on the turbo is a good thing to do, if you're pedaling constantly at a certain cadence then the power should not fluctuate much at all.

bristolpete

NP is your friend. To a point.