Favero Assioma Pro RS-2

If you want accurate power measurement on your bike then the Favero Assioma PRO RS-2 pedals are pretty hard to beat, really. They’re cheaper than most power pedals, lighter than most pedals full stop, and accuracy is on point. You can even morph them into SPD pedals by swapping the bodies.

Favero’s Assioma PRO RS-2 pedals are SPD-SL-compatible road pedals built around Favero’s Assioma PRO spindle. Where before the electronics were in a kind of pod by the crank, now the power sensing, battery and communication are all packed into the axle, and you simply add a pedal body you can clip into. We’ve already reviewed the PRO MX-2 pedal, which uses the exact same spindle with a double-sided SPD body, and Aaron was impressed with those. Very impressed.

These pedals use a composite SPD-SL body with a Q factor of 53mm from the crank (you can pad that out to 55mm with the supplied spacers) and a stack of just 10.5mm.

Because all the expensive bits are in the spindle you can buy replacement bodies for the pedals for around £40 a side, or if you wanted you could keep a set of SPD bodies in the shed to swap out for your mountain bike XC racing career, if you’re Tom Pidcock or something.

One of the main benefits of pedal-based power meters is the ease of switching from one bike to another, and with swappable bodies too there’s no reason why one set of pedals (and a spare set of bodies) couldn’t measure power on any bike in your fleet with a bit of faffing. That’s quite the USP.

These pedals are very light. Our set weighed exactly what Favero suggested they would: 247g, or 123.5g per pedal. To put that into perspective that’s lighter than both the 105 pedal (160g) and the Ultegra pedal (136g) that I pulled out of the bits box in the shed, and also lighter than the Garmin Rally pedals (160g) that are their most direct competitor. Dura-Ace pedals are claimed to be lighter – I don’t have any to check – but only just.

The weight is impressive considering how much tech is packed inside. There’s the power sensing circuits of course, and Bluetooth and ANT+ connectivity to link with your head unit. A Bluetooth connection will give you basic power numbers, but you get a whole ton of metrics via ANT+: left/right balance, pedal centre offset, power phase, pedal smoothness and torque effectiveness. If you like to work on your pedalling efficiency then there’s plenty of data to analyse. The Favero app will display all these metrics for you too.

The rechargeable battery in each pedal is good for around 60 hours, and you charge it by connecting a magnetic cradle to the spindle which accepts any USB-C lead; Favero provides a double-ended lead so you can do both pedals at once.

You get a set of cleats too, but any SPD-SL cleat should be fine, and there’s a standard tension adjustment in the sprung clip to adjust the release force. Float is determined by the type of cleat you run. In terms of their use just as a pedal, they’re pretty normal.

You have to fit them with a pedal spanner because there’s a status LED where the hex socket might otherwise be, and you have to torque them up nice and tight. But in use they’re easy to engage and the range of clip tension is good. They have a nice positive click too.

The bearings are nice and smooth, and they’re simple to strip down and regrease should you need to. We should expect them to be competent pedals, so no surprises there, but what you really want to know is: what’s the power accuracy like?

Favero Assioma PRO RS-2: Power accuracy

I’ve been benchmarking the Favero Assioma PRO RS-2 pedals against a couple of things during testing: the latest Wattbike Atom Uplift, which is also in for review, and the SRAM Rival power meter aboard my Lauf Úthald endurance road bike. I’ll point out at this juncture that these are relative tests: I don’t empirically know whether any of these power meters is exactly right. Both the Wattbike and the Lauf have given me very believable numbers though, and repeatedly so.

Against the Wattbike first, here’s a trace of a session in Zwift where I’m just riding around:

There’s only a couple of watts in it between the two overall, and they track each other more or less exactly. The pedals read slightly higher than the bike, but there’s only 1% or so in it. In theory the Wattbike should read lower anyway, as the power meter is further down the transmission, so you’d expect losses.

The mean max power graph for that ride shows no major difference at any point in the curve.

Cadence measuring is also on point, with no issues or dropouts.

For the trainer in ERG mode it’s the same story, more or less: a slightly bigger discrepancy, with the pedals reading higher again, but we’re still only talking 2% between them.

Here’s a long (seven-hour) ride outside, recording from the pedals and also the SRAM Rival crank-based power meter. Overall the pedals read under the cranks, and the difference is bigger, around 5.5%. I think this is mostly to do with the way the two power meters handle low power and zero power, and the transitions in and out of it.

If we zoom into a section of that ride that’s a more constant effort, then the gap closes considerably, to around 1.5%, with the cranks still on top. There are a couple of points where they obviously don’t agree but for the most part everything maps pretty well.

The mean max power graph for that ride suggests that around about 150W average the pedals start to read a bit lower than the cranks and that’s the main source of any discrepancy, although the pedal line (blue) is the lower one right across the board. Remember that the mean max power graph is the maximum average power over a certain time, and for a long ride like this, and in the long tail, it will certainly include plenty of time at zero. If we zoom in to a point in the ride where I am turning the pedals, but not pushing hard (after the cake stop, along the flat levels roads, with a tailwind) we can see some trends:

Firstly, the pedals read below the cranks, which we’d expect from everything else we’ve seen. Secondly, the pedals seem to be much keener to back off the power: you can see the troughs between power peaks are much deeper here on the blue line. That might just mean they’re more sensitive in this specific regard, or they just interpret the same thing differently. Anyway, it’s the main reason for the gap in the average power numbers when you’re not pushing hard. I didn’t see a similar pattern when I was benchmarking the pedals against the Wattbike, which suggests the cranks are over-reading in those situations, not the other way round.

The only time the two power meters didn’t match up very well at working power was on the final climb, when for whatever reason the pedals were reading 6% lower as I slogged up my last hill before hosing myself down in the garden to cool off. It was pretty hot at this point, so it’s maybe to do with how the two power meters reacted to the increase in temperature, although really it shouldn’t affect either. It’s the only time I ever noticed a real discrepancy during testing, and I did other hot rides where it wasn’t an issue.

Here’s another ride, which was a quick hill interval session outdoors. The discrepancy overall is again nearly 6%, but for the intervals themselves (which were quite short, so there’s more statistical noise) the discrepancy was around 1.5% overall in favour of the cranks, with a couple of the intervals nearing 3%. A similar pattern.

What does all this mean? Well, of the three power meters the Favero pedals sit in the middle: they read under the Rival cranks and above the Wattbike. The cranks are the biggest outlier, but it’s not a big gap when we’re talking about the points in a ride where you want to look at your power numbers and know they’re accurate. There are some discrepancies at the low end of the power scale but once you’re up into your work, they more or less disappear, and I’d say that it’s probably the pedals that are doing the better job of reporting what’s really going on.

Favero Assioma PRO RS-2: Battery life and charging

One of the downsides of the Favero design, with everything in the spindle, is that there’s not a huge amount of space for a battery. That’s reflected in the battery life, which is a claimed 60 hours; I got close to that in summer conditions, but in the cold of winter it’s going to be a fair bit shorter. Is that going to be enough? Not for riding to power for the whole Transcontinental Race or something like that, but you’re good up to a 600km audax, or a week-long tour, on one charge, so most bases are covered.

The IP67 rating of the pedals is welcome – pedals see some harsh conditions – and the use of a magnetic charging cradle rather than a vulnerable standard port is eminently sensible. With the supplied double-headed USB-C lead you can charge both pedals at once, and it only takes a couple of hours (exact time will depend on what you’re charging from) to fill them up again; the batteries aren’t big, so you can easily charge them from a battery pack if you carry one.

They don’t last as long as some of the other power-measuring options, and you don’t get the simplicity of a replaceable battery as you do in some other systems, but I haven’t really had to think about it too much, and realistically your pedals running out of juice on a ride is going to be an annoyance rather than a catastrophe. The pedals report battery charge to the Favero app or a head unit, so it’s easy enough to check.

Favero Assioma PRO RS: Value and overall

The £649 RRP isn’t small change, but for a double-sided pedal-based power meter it’s pretty good value; you can go single-sided for around £200 less if you don’t need to know which of your legs is doing the heavy lifting.

The price of power pedals has been coming down in the past few years and some pedals, like the £399 Magene pedals we haven’t yet tested, are quite a bit cheaper than this.

But the Assiomas are undercutting the likes of Garmin RK200, Look and Wahoo at this price.

If you already have a bike setup you’re happy with and you want to add a power meter without going through the rigmarole of swapping out your chainset, then these Favero pedals are a good bet.

Conclusion

If you want to measure power on a number of bikes – and especially if you want to use SPD pedals on some and SPD-SL pedals on others – then I’d say the Assioma PRO RS-2 pedals are currently the top pick. The power readings they give are on the money, and they’re light, reliable and easy to use. You’ll need to charge them a bit more often than some other systems but that’s the only real downside.

Verdict

Excellent double-sided power pedals that are light and reliable

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