Buying a second power meter (4iiii)

So my situation is that I’ve been training with a 4iiii Precision left-only power meter for several years on my indoor training bike. I’m adding a gravel bike to my stable and am planning to get another 4iiii power meter. My question is whether I should buy the dual sided option, or stick with the exact same single sided power meter? I’m hoping to get power numbers as close as possible between my indoor training bike, and the new gravel bike.

That’s the question. How does one achieve that? I’ve tested three power meters and two smart trainers and they all diverged to various degrees. Most were withing 5-10 watts but one trainer was off by a lot.

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you could always go with something like the Garmin rally power pedals if you want to invest that much. You can transfer those between bikes and pedal types.

I have favero assioma pedals for my road bike which mostly sits on my trainer. The assioma ped power matches very closely with my elite direto trainer. On my gravel bike I have a left only crank arm power meter. Honestly, on gravel rides I don’t do that much power training. I do it some and my left arm crank power meter is reasonable close. For me, I’m not worried about it being perfect. I know what should feel hard and what shouldn’t. And for me that’s enough for those outdoor longer rides.

If I was really concerned I’d get the rally pedals and use them for everything.


Fair point on the pedals, although they are quite pricey and not without compromises.

I bought a second 4iiii left only PM, and don’t see too much difference between both bikes, on a hill close by. My test is to ride at the same average power and see the time difference, or to see my average power when pacing the live segment against my PB. It’s marginally different, as in 1-2 seconds, or 5-8W over the 2.2Km segment.

If you have 2 left only precision power meters their accuracy should match very closely. If it was me, I’d just do that and call it a day. I think people get hung up on a few watts in either direction. I think it’s easy to control watts on a smooth paved surface like road biking but when you get on gravel it’s much harder because the terrain can vary between small or big gravel, sandy, clay, mud, etc. and trying to hit some power target in that situation becomes hard.


Me personally, I would go single sided. At least it will be reasonably comparable.

But I am not nearly as hung up on accuracy as a lot of people. I have four very different PM’s on four very different bikes (pedal, two different brand of crank arms, and spindle). I test on one (which ever is convenient at the time) and just use that number for everything. If I am off +/- 2-3% across the different meters, I don’t know it nor care. I guess I am more of a hand grenades type of user.

Here is the reply that I got from 4iiii support, for those that are interested.

Hi Russell,

I am not sure how to answer that question for you because there are too many factors to eliminate. For instance: are both bikes identical in their geometry, set up, installation, riding position, material fatigue, damage to the crank, age of device, quality of battery etc.? Anecdotally, as a bike mechanic, I saw manufacturing differences between bikes even within the same make/model/year depending on the quality control (and price point) of the bike. So to aim for identical results between bikes might be tricky to achieve.

Our powermeters are accurate to +/-1% and we are pretty confident about that claim. When I am building my training program I know that my power numbers will be different between ‘species’ of bike ie: my gravel will be different than my road and different again to my mountain bike. So I compare my power numbers to previous rides on that same equipment but never between bikes.

For the most part my numbers will be similar but never identical. Now, obvioulsy I don’t know you as a rider or what your goals may be so I invite you to open this question up to your coach or riding buddies to see what their input might be.

I hope that helps, have a nice weekend.

I’d go with a quarq dzero/dfour and you can always alter the setting to match the 4iiii if you find they are different. I’d be careful though because the quarq will be loads more accurate than a left only 4iiiii.

I have assioma duos on my road bike but I went for a quarq dzero to get the best possible accuracy/reliability and the added benefits of a spider based power meter on a gravel bike.