The Best Single-Sided Power Meters

The Uno is the Assioma Duo with one sensing pedal instead of two. Same body, same spindle, same IAV measurement principle, same ±1% claim on the leg it reads. That shared lineage is why it sits first: you are not buying a cheaper design, you are buying half of a good one.

The practical advantage over every crank-based pick below is that it has no compatibility question at all. If your bike takes pedals, it takes these. That matters most for riders who own more than one bike, because the meter follows you from the summer bike to the trainer bike in about five minutes.

The constraint is the cleat. The Uno is a Look Keo-pattern pedal, so Shimano SPD-SL riders either change shoes or buy something else — our cleat compatibility guide maps the whole field. If you want the dual-sided version of this argument, read Assioma Duo vs Uno.

A bonded crank-arm meter is the quietest way to own power. It weighs 9 g, sits 5.5 mm proud of the arm, runs for a claimed 800 hours on a coin cell and never asks you to think about it again. For a rider with one bike and pedals they like, that is a better life than a rechargeable pedal.

The price of that is the order form. 4iiii bonds the sensor to a specific crank arm, so you are buying a crank: wrong model or wrong length and it does not fit. Check both carefully, and check frame clearance if your bike has short chainstays.

It is the natural comparison point for the Assioma Uno, and we have run that comparison in full in 4iiii Precision vs Favero Assioma.

Garmin sells the Rally in bodies rather than in systems, so the RS110 is the single-sensing version with a Shimano SPD-SL body. For a rider whose shoes are already set up for SPD-SL, that removes the one objection to the Assioma Uno.

The internals are the interesting part: Garmin uses the same sealed rechargeable spindle across the range, so the measurement and the claimed ±1% do not change between the 110 and the 210. You are paying for a second sensing spindle, and you can buy that later instead.

The counter-argument is price. A dual-sided Favero pedal often costs less than this single-sided Garmin, and that is the trade you are making for ecosystem fit — see Favero Assioma vs Garmin Rally for the full version.

The P505 belongs on a single-sided page for an awkward reason: it is not single-sided, and that is exactly why it is useful here. A complete crankset carries gauges on both arms, so it reports genuine left/right balance — the one thing every other pick on this page estimates by doubling.

The tolerance is wider, at a published ±1.5%, and for most training purposes that is a smaller problem than the doubling error it removes. If you specifically want balance data without paying dual-sided pedal money, this is the route.

The cost is a crankset swap and a bottom bracket conversation. If that sounds like more than you want to take on, buy the Uno and accept the doubled number.

If your bike already runs SRAM DUB, this replaces one crank arm and the spindle and leaves everything else alone. It is the least invasive crank-side installation on this page, and the cheapest branded one.

We rank it last on measurement for a specific reason rather than a vague one: we could not find an accessible published accuracy tolerance for this unit. That is not the same as saying it is inaccurate, but a number we cannot cite is a number we will not quote, and every pick above it publishes one.

Check the crank length before ordering. The listing is 165 mm, which is shorter than most riders run, and crank length is not a spec you can adjust later. Best power meters for SRAM bikes covers the rest of the range.