Favero Assioma Duo Shi power meter review: BYO Shimano SPD-SL pedals

by Dave Rome

photography by Dave Rome


Most performance-level bikes don’t come with pedals. And Favero’s latest power meter pedals also don’t come with pedals. Wait, what? 

Story Highlights

  • What: Independant left-and-right pedal-based power meter that installs into Shimano road pedals.
  • Key features: Same power meter technology as the original Favero Assioma but in a package to suit Shimano SPD-SL pedals. ANT+ and Bluetooth connectivity. Auto calibration. Claimed 1% accuracy.
  • Weight: 313 g with Shimano Ultegra R8000 pedal bodies (adds 65 grams over stock pedals).
  • Price: €495,00 (plus VAT), Shimano pedal bodies and cleats not included.
  • Highs: Combines Favero’s proven power tech with Shimano’s proven SPD-SL system, reliable metrics, competitive weight, known pedal feel and function.
  • Lows: Greatly increased Q-factor, unknown durability of bushing-based bearing system.

It’s no secret that Favero – makers of the extremely popular and proven Assioma power meter pedals – were working on a Shimano SPD-SL-compatible version. We caught wind of such a product in an accidental leak, and then the Italian company teased the product themselves. And at long last it’s official, giving Garmin’s new Rally RS pedals some competition for those wanting to run both power pedals and the SPD-SL cleat system. 

The new Duo Shi joins the existing Assioma (Look Key-based) pedals in the range and uses much of the same proven technology. What’s obviously different is that where the Favero pedals were actually whole pedals, the new Duo Shis are just the power-based spindles that you install yourself into the bodies of authentic Shimano pedals you probably already own. Yep, these pedals aim to offer an almost indistinguishable riding feel to the most popular road pedals on the market. Well, almost. 

Before I dive in let me preface this review by saying that if you’re looking for comparative power data for how the numbers of these pedals stack up against other power meters, head over to DC Rainmaker or GPLama – I’ll only briefly touch on this element. Instead, my assessment predominantly focuses on the installation, usability, and compromises of this new product and how it compares to stock Shimano pedals and Favero’s pre-existing Assioma pedals.

Why Shimano SPD-SL? 

Before I cover the details let me first answer the big question: why Shimano SPD-SL? Favero already offers well-proven power meter pedals based on the Look Keo System, so why all the trouble? 

Shimano’s SPD-SL system isn’t the lightest, the most adjustable, or the most aero road pedal system, and yet, it is the most popular. The popularity is certainly related to Shimano’s market dominance, but that’s far from the whole story. 

Shimano’s SPD-SL (pictured on the right, Look Keo on left) cleat is just one of the reasons for the system’s popularity. The generous width doesn’t just provide a stable platform on the bike, it’s more stable on foot, too.

My preference for Shimano’s SPD-SL system is something I’ve covered in my review of the Dura-Ace R9100 pedals, and basically, it comes from the pedals doing the most important things right and being the most set-and-forget. The wide pedal body (approx 8 mm wider than the Look Keo) provides a stable connection to the cleat. The cleat security and ease of locating the pedal are better than most. The stack heights are competitively low. 

But more importantly, the pedals are extremely durable and the internals are serviceable (not that they need much attention). The three-bolt cleats are simple and safe to walk in. And the system tends not to suffer squeaking, creaking, or off-axis toggle in the cleat like Look Keo or others can. 

Perhaps most importantly it’s the system that more riders use than any other, and those wanting to add power to their bikes may not want to do so at the expense of changing out a contact point – especially if they have multiple bikes on the go. This is surely why Garmin’s new Rally power meter pedals are available in a Shimano SPD-SL version, and why Favero has created such a product, too. 

An intro to the Assioma Duo Shi

The new Assioma Shi spindles are designed to be a direct fit with the composite bodies of Shimano R8000 (Ultegra), R7000 (105), R6800 (previous gen Ultegra), R550, and R540 road pedals. Notably, Dura-Ace pedals, which use a different axle design, are not compatible. Likewise, Shimano’s off-road-going SPD (two-bolt) pedal platform uses an axle with shorter proportions and also isn’t at all compatible (probably for the best – the power pod would likely come into contact with rocks …). Favero will only be selling its power-equipped axles – it’s BYO for the Shimano cleats and pedal bodies. 

Where Favero offers its original Assioma pedals as either a left-side power measurement (Uno) or dual-sided measurement (Duo), the Duo Shi, as the name suggests, is only available as a dual-sided option.

All the electronics are contained within the circular pods.

If you’re familiar with the features list of the pre-existing Favero Assioma, then you already know the features list of the new Duo Shi. With independent dual-sided power measurement, the axle-based pods offer both Bluetooth 4.0 and ANT+ connectivity. Accuracy remains at a claimed 1%, something that Favero says is possible due to its “​​Instantaneous Angular Velocity-based” measurement that doesn’t use averages to assess power transfer through the pedal stroke. Like most power meters, cadence measurement is covered, while the pedals also offer automatic temperature compensation, automatic zero-reset, and feature an in-built gyroscope (which assists with the angular velocity measurement).

Like before the rechargeable battery and electronics are permanently bonded to the axle and are not serviceable. Those electronics are resin-filled to ensure they remain weatherproof, and with a claimed IP67 rating you could probably go swimming with them. Battery life sits at over 50 hours between external charging, and the pedals are auto off-on based on movement. 

What is new for Favero is how the axles install into Shimano’s own bodies, and this required a different factory calibration – which is why Favero is unable to offer a conversion kit for existing Assioma owners. The bearing system is also quite different from the original Assiomas and from Shimano’s own designs, too – something I’ve covered below. 

Shimano’s cup-and-cone bearing system (right) allows for a slim axle profile. Favero had to make some design changes in order to match those dimensions.

Using Shimano’s own pedal bodies means that Shimano’s stack heights are unchanged. I say this as plural because the stack heights of Shimano pedals change based on iteration and price. For example, Dura-Ace R9100 (which can’t be used with the Assioma Shi) sets the benchmark with 8.8 mm pedal height, R8000 pedals sit at 10 mm, while the older 6800 pedals are 10.7 mm. For comparison, Favero’s Look Keo-based Assiomas sit at 10.5 mm (pedal height), while Garmin’s new Rally RS is at 12.2 mm.

Stack height may remain unchanged, but Q-factor (the stance width of the pedals) absolutely does not. Combining the external power pod and Shimano’s own pedal bodies forced Favero to make one large concession – and the width of each pedal has grown considerably by 13 mm. The result is a pedal with a Q-factor of 64-65 mm (64 mm for 105 or lower, 65 mm for Ultegra), a far different figure from the 53 mm of Garmin’s Rally RS pedals. This figure is quite substantial and so I’ll return to what this means. 

The Q-factor is going to be a sticking point for many. On the left is the Assioma Duo Shi, on the right is the regular Assioma Duo.

The new offering is roughly comparable to the regular Favero Assioma Duo (304 g) on the scales. A pair of Duo Shi axles weigh 198 g and with Shimano R8000 (Ultegra) pedal bodies they weigh 313 g. That’s a 65 g addition over a regular pair of R8000 pedals. By comparison, Garmin’s new Rally RS200 (SPD-SL) power meter pedals are claimed at 326 g. 

Pricing is a little bit less than the regular Assioma Duo, but perhaps less so than you’d expect given the pedal bodies and cleats are not provided. The new Duo Shi spindle kit will sell for €495 (plus VAT), while the original Assioma Duo is priced at €569 (plus VAT). 

 Installation 

Favero’s new Assioma Duo Shi is shipped in the same detailed cardboard packaging as the other Assioma pedals. As noted, you won’t find any pedals or cleats inside. Instead, the box contains left and right pedal spindles, each with the Assioma power pods permanently bonded in place. 

Go a layer deeper in the box and there you will find many of the same items that the pre-existing Assioma pedals include. There’s a number of manuals and instructions in various languages. There are two identical USB-based proprietary charging cables, a two-port USB wall adapter with all the common international plug fitments (meaning both pedals can be charged simultaneously), a series of optional pedal washers (only needed for certain cranks), and a long 8 mm hex key for installing the soon-to-be pedals into your cranks. 

All that’s included in the box.

Depending on the Shimano pedals you’re trying to convert, what’s missing is the 17 mm open-end wrench (for Ultegra-level pedals) or Shimano TL-PD40 pedal service tool (for 105 or lower) required to remove the stock axles and the attached bearing assembly. Shimano’s road pedals are intended to be serviced and so opening them up is not a big deal – assuming you have the tools. That TL-PD40 is a plastic tool that often sells for a couple of dollars. Alternatively, a decent multi-grip plier and a rag can be used with care. 

Also missing is a 19 mm open-ended wrench required to install the Duo Shi axle units. Instead of the included 8 mm hex key (which almost every cyclist hopefully already owns), I’d prefer to see Favero include a 19 mm crows-foot wrench so that you can use a torque wrench to tighten the axles into the Shimano pedals.

Removing the stock axles is simply a matter of unwinding the exposed nut in the opposite direction to the arrow printed on the pedal body. There’s quite a long length of thread (often treated with a thread locking compound) here and so it’s typical to feel quite a bit of resistance while undoing this nut. Once undone the axle and the contained bearing unit will pull out from the pedal body. 

An arrow on the pedal body shows you which way tightens the axle.

From here you simply reverse the process with the Assioma Shi axle unit in hand. Take care to ensure you’ve got the correct left or right side. The whole process should only take a few minutes (assuming you have the right tools). Your now-power-equipped Shimano pedals are ready to be installed on the bike. 

Favero provides a small number of pedal washers to use in case of clearance issues between the crank arm and power pods. These weren’t required with Shimano crank arms, but take care and watch the gap when installing on other cranksets. 

Mind the gap. There needs to be a millimter (or more) of space between the crank arm and the power pod.

You install these pedals just like any other pedal, and Favero doesn’t request that you use a torque wrench to do so. You can now ride your bike, but there is a must-do step before you can see your power figures. 

Just as with the regular Assiomas, Favero blocks data transmission from the pedals until you register them. I found this an unexpected and somewhat annoying step with the original Assioma pedals, but it does ease Favero’s ability to offer remote support if ever needed at a later point. Registration is a painless process through Favero’s own phone app, and the app wirelessly handles any available firmware updates, too. The app is easy to use and gave me no cause for complaint. 

You’re now ready to ride, assuming you’ve charged the batteries. Charging couldn’t be simpler and there’s no risk of damaging electrical contacts or plugs by getting it wrong. The two provided charging connectors are magnetic and simply need to be aligned with the two exposed metal contacts on the pedal pods.

The provided USB charging cables are generously long so that you can leave the pedals on the bike and they’ll safely unclip themselves in the event someone trips over them (oops). Those cables also use a Micro-USB at the magnetic connector plug end (see second gallery image below), so it’s easy to swap them to a shorter option or separate them for storage and/or travel. 

Favero found that there may be a mechanical settling period with its axles going into varied Shimano pedal bodies. The Italian company suggests that its expected standard of power accuracy will be reached after the first couple of rides (or the first long ride). They don’t specifically say the pedals need to be re-calibrated (done through your head unit or phone), but doing so is likely a good idea after the first ride. 

Riding the Duo Shi 

The pedals are obviously easy to install on just about any bike, and getting them paired to most common head units or phones should be problem-free, too. As expected the Duo Shi’s connected without hassle to Wahoo Elemnt Bolt and Roam head units, but were also quickly found by the sometimes fussier Bryton and Lezyne head units, too. 

As mentioned at the beginning of this review I won’t be going deep on the power measurement side of things – it’s not my field of expertise. However, of the power meters I own, the regular Favero Assioma is the one I deem to be most accurate and this is supported by the fact that DC Rainmaker and GPLama both use these pedals when benchmark-testing other devices. Me testing one power meter against one or two others that are assumed to be accurate is not a scientific measure of accuracy, and so I’ll leave such judgement to those who test power meters on a regular basis. 

That said, I’ve found the Duo Shi to track in line with where the Assioma Duo does. Both units sat at consistent figures higher than what a Wahoo KickR 18 recorded. My left-right percentage balance is identical between the two. And both record comparable maximum figures in a sprint, at least as close as you can expect given the change in cleat systems, shoes and bike fit – this isn’t exactly an apples-to-apples comparison. 

Alright, so from what I’ve seen I’m happy to trust the power data just as I do with the standard Assioma Duo pedals. And they’ve behaved much like I’ve come to expect from the regular Assiomas that I ended up buying after my review. They really are a set-and-forget power meter. Well, with the exception of the alien flyer saucer aesthetics and the flashing LED lights.

Some don’t love the aesthetics of Favero’s design. I’m often fine with function over form.

Perhaps the only time they require more specific attention is during travel (ironically I’m writing this while in Sydney’s lockdown). The pedals turn on from movement, and so overly long across-country drives or flights can deplete the battery charge. Favero’s app allows you to switch off the pedals through its “Travel Mode” but the USB charging connector will be required to wake them again. Thankfully you only need one connector, which happens to be small and can be used with any Micro-USB cable. 

Clipping in and out of these pedals is entirely unchanged from when the pedals had their stock spindles in place. Favero’s own bearing system doesn’t introduce any play or rocking at the pedal body, and things spin comparably free, too (at least after a few rides). The angle at which the pedal hangs awaiting a cleat is seemingly unchanged, too. 

The hanging angle of the pedal is unchanged as the weight distribution is the same.

The ride feel, cleat stability, and easy pedal locating that Shimano pedals offer are all consistent with the Assioma Duo Shi, and it’s a welcome change from the regular Favero Assioma. It truly is nice being able to clip into such a refined and proven pedal body. 

That all said, while so much feels identical to a stock pair of Shimano pedals, there’s just no ignoring that increased stance width.

An increased Q-Factor 

Q-Factor is effectively the stance width when pedalling a bike. While commonly overlooked, it’s a highly personal element to bike fit that can play an important role in muscle activation and how your knees align with your feet and hips.

On the road, Q-factor has seen a subtle increase in recent years and things are not getting narrower. Most Shimano road cranks offer a Q-factor of 146 mm, and the nearest competitors aren’t far off of this. Meanwhile, the stance width in mountain biking is seemingly forever growing as tyres widen, and even the most competitive-focussed endurance race bikes now sit some 18 mm wider from one crank arm to another when compared to a road bike (and most modern mountain bike cranks are 24 mm wider).

You’d think such an increase is detrimental to performance, but the likes of Mathieu van der Poel and Tom Pidcock don’t show any issue in jumping between the different stance widths forced by different disciplines. 

And that leads us to current road pedals and where Favero’s new Assioma Duo Shi sit (or don’t) in the mix. 

Stock Shimano Ultegra and Dura-Ace pedals offer a Q-factor (measured from where the pedal axle meets the crank to the centre of the pedal body) of 52 mm. Shimano also offers the same pedal with a wider “+4 mm” spindle that produces a 56 mm Q-factor.

Look Keo pedals sit at the 53 mm mark, as do Garmin’s new Rally power meter pedals. Meanwhile, Favero’s standard Assioma pedals have a Q-factor of 54 mm. 

Speedplay pedals have long been a favourite of many bike fitters, mainly because the pedal system allows for a great range of fit-tuning options. In stock form they feature a 53 mm Q-Factor, but historically the company offered aftermarket axles that catered to Q-factors from 50 mm and up to 65 mm. Since Wahoo’s acquisition of Speedplay, that narrowest 50 mm option has been discontinued due to a complete lack of sales demand. 

Still, what’s obvious from all of these examples is that most road pedals sit around the 52-56 mm range. Meanwhile, Speedplay’s longest customisable option is 65mm – the same figure as the Assioma Duo Shi. That’s a figure that applies to both pedals, and means you’ll likely be adding 26 mm to your stance width compared to a regular pair of Shimano pedals. 

A regular width Shimano R8000 on the left and the outside Favero Assioma Duo Shi on the right. It’s quite a difference!

According to Shimano, “The best way to determine the right axle length for you is to visit a qualified professional bike fit specialist who can evaluate your biomechanics and let you try both pedal types. The +4 mm longer axle pedal type is often preferred by athletes with naturally wide hips, large quad muscles, or those who simply don’t feel comfortable with their feet close together. For these athletes, adding axle length helps to maintain correct leg and foot alignment, aiding in efficient power transfer and low joint stress.”

“Wow! That’s pretty extreme,” was the immediate reaction from veteran bike fitter Stewart Morton (owner of Melbourne-based fitting studio RiderFit) when told about the Favero Duo Shi’s 65 mm width.  

Well, at least you won’t have to worry about crank rub…

“A lot of people don’t consider the frontal plane of riders,” said Morton in reference to bike fit. “They look at the side of the rider. When you look at the relationship between the hip, knee and foot, if the foot is sitting out too wide, your knee is being pulled out wider than it wants to be.”

Morton suggested an extra two, three, or even four millimetres is probably quite good for a lot of people, but that very rarely does he see people that can benefit from going wider by 10 millimetres or more (such as Speedplay’s 65 mm axles). 

Of course, there is a small amount of side-to-side adjustment in the cleat system, and it’s likely you’ll be able to gain back a few millimetres by moving the cleats to the outer edges of your shoes, but this won’t overcome the majority of the width increase. 

I personally ride mountain bikes and gravel bikes just as much as road bikes and am used to pedalling a wider Q-factor. I don’t give a second thought to jumping between my wide-stance mountain bikes and narrower road bikes. And yet, the change to Assioma Shi pedals brought a noticeable difference to how my bike felt. Most importantly the Duo Shi pedals changed where my feet sat in relation to my knees, and it somewhat exaggerated my knock-kneedness on the bike. 

Another width view. Here a regular R550 sits on top of the converted Duo Shi pedals.

I can’t say whether the Assioma Duo Shi’s wider stance width will be a fine or problematic change for you, but I can say that the pedals will effectively match your road bike’s stance width to that of a mountain bike. I suspect with enough time I’ll get used to it, but I’m not sure I want to.

Morton’s point of view backed my opinion, which is if your knee alignment is good with common width pedals, then making a rather big positional change from where the foot needs to be is probably not the right move. However, Morton did suggest that the wider width could be of benefit to select riders who could unknowingly benefit from such a change in fit.

The unknown: bearing durability 

Where the increased stance width is an obvious concession, the change in bearing system is far easier to miss. And while it’s far too early to say for certain, I have my concerns for the long term durability of Favero’s bearing system for which the Shimano pedal bodies turn on. 

There’s no denying that Shimano’s own cup-and-cone bearing system is the market benchmark for reliability and durability – there is no other pedal system that comes close. Meanwhile, the regular Favero Assioma employs two sealed bearing cartridge units which have proven surprisingly durable, and then easy and cheap to replace if needed – an identical design to Xpedo’s NXS pedals. 

But in order to fit an axle into Shimano’s slim (and low-stack) pedal bodies, Favero was forced to move away from the dual-bearing configuration in exchange for something slimmer. The result sees a sealed cartridge bearing on the outer end of the axle, and then a nylon bushing on the inner side. A single 9 mm nut (M6) holds the bearing assembly onto the steel axle. 

A fixed bushing sits in place of a bearing on the inner side of the pedal.

That bushing brings up a few unknowns in regards to long-term durability. According to Favero, the bearing and bushing are integrated with the adapter (or cartridge), and so if wear were to occur you’d replace the whole aluminium bearing cartridge that threads into the pedal body (pricing TBC), not just the worn pieces. 

Replacing that cartridge is a pretty simple task and isn’t likely to be big money, but where my concern lays is over spindle wear or grooving as a result of the bushing turning directly on it. This issue is something I used to experience with the titanium spindles of early generation Crank Brothers pedals which used a comparable internals design (although admittedly rarely did I see the issue with those running steel spindles). 

For Favero, there are a few things that should work in their favour versus those older Crank Brothers pedals. Firstly the bushing used here is longer and supports the load over a greater section of the spindle. Secondly, the external sealing for the bushing is hugely better. Favero has actually machined an “oil retainer” (or step) into the axle so that the system isn’t relying on a rubber ring to do the sealing – an O-ring sits in the groove of this machined retainer. And lastly, these are road pedals that won’t see anywhere near the same continuous muck and grit as the early mountain-bike-focussed Crankbrothers pedals. 

Favero has gone to great efforts to ensure the bushing lasts. This seal step is machined into the axle.

Only time will tell if this is an issue of concern or if I’m worrying for nothing. In the short-to-medium term, Favero covers these pedals with a two-year warranty. Longer term you’ll want to pay attention to any play forming between the pedal body and spindle, check the tightness of the bearing-retaining nut to remove any play, and replace the bearing cartridge before unwanted wear can occur to other parts of the pedal system. 

Wrap up 

I applaud Favero’s efforts to adapt its power measurement system to directly fit with Shimano’s pedals. That combination brings one of the easiest-to-use and best-performing power meters on the market to the most popular pedal system. 

I know many of you were waiting patiently on this marriage, and I suspect many of you will be disappointed to learn that there is one rather obvious downside to this power couple. 

While I have no doubt that Favero has done its homework, I still can’t shake the feeling that the increased Q-factor and to a lesser extent the bearing design were compromises that could possibly have been mitigated through creating their own compatible pedal body. Garmin has done so, and while there are trade-offs there (such as the increased stack height), I suspect the market will be more accepting of that than a vastly wider stance. 

Still, in its current form there’s a whole lot to like here and Favero has proven itself as a trustworthy name in the power meter game. Pedal stance is a highly personal element that only you (or your bike fitter) can say is a deal-breaker or not. And if you’re OK with the wider stance, then you’ll love the new Assioma Duo Shi. 

Note: Currently the only other power meter pedal on the market to use Shimano’s SPD-SL cleat system is Garmin’s new Rally pedal. I’ve arranged a review sample with Garmin in the hope of doing a comparison but unfortunately, they are yet to arrive. This is something I plan to revisit in the near future.

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