SRM X SPD Power Meter In-Depth Review

Its been a long time since a major brand new power meter was announced, and today’s post…well…it doesn’t change that. In fact, the SRM X was announced some 18 months ago, and started shipping in super limited quantities nearly a year ago. I’ve been riding it pretty consistently since last spring, albeit on a few different pairs (more on that later). Thus, I have substantially more data than I typically do for a power meter review.

While the SRM X is notable as the first SPD based pedal power meter, it’s also notable for SRM themselves: It’s really their own design. Unlike the SRM EXACT power meter, which was built in partnership with LOOK, this unit (the SRM X) is fully SRM technology. That means it does away with LOOK’s finicky to deal with design, which has been around the block in various incarnations over the last decade, first with a Polar partnership, then sold briefly by just Look themselves, and finally, with the SRM EXAKT road pedals a few years back.

But again, these pedals aren’t that. SRM says their internals are different – and one only need to install them to see that. There’s no funky tools required like of years past, nor any weird setup procedures. Just install, do a few second one-time setup step, and you’re done. It doesn’t matter whether you’re riding SPD pedals for road or off-road purposes, the functionality is identical. My testing covers both, though skews slightly more road-focused simply because I lack meaningful mountain bike trails where I live (and currently can’t travel to places with better trails).

In any event, once I’m done with this loaner set for this review, I’ll box it up and send it back to SRM. Just the way I roll. If you found this post useful, consider becoming a DCR Supporter which makes the site ad-free, while also getting access to a mostly weekly video series behind the scenes of the DCR Cave. And of course, it makes you awesome.

Unboxing:

The SRM X power meter comes in either a dual or single-sided option. For this review, I’m testing the dual-sided version. Whereas if you buy a single-sided variant, you’ll get a second identical pedal but without any electronics inside it.

Crack open the box and you’ve got the pedals looking back at ya:

Inside the box there’s a slate of parts. Essentially there’s the pedals themselves, two long micro-USB charging cables, two charging pods (which use micro-USB), and cleats. Oh, and a little paper manual.

Here’s a closer look at those parts. First, the pedals:

Then we’ve got the cleats and charging pods:

Those pods attach to the extra-long micro-USB cables, which are 3 meters long:

And that’s all there is to it. We’ll get them installed in the next section.

(Note: You’ll see two different sets in the review. The black set was my first pair I started on last Feb/March, and then after some issues I received a new set last summer, which was blue. More on those issues later.)

General Use Overview:

First up is getting the SRM X installed, and I’m happy to report that unlike the SRM EXAKT road pedals, the SRM X is just like every other pedal: Simply install it, firmly. There’s no special installation tools or such here like the EXAKT or previous LOOK-based pedals.

Because the spindles house the electronics, you will need to use a pedal wrench (as opposed to an Allen wrench into the spindle). But I suspect most people considering a pedal based power meter will have a pedal wrench. If not, they cost $15-$25 and you can also use it for breaking blocks of ice up, once partying resumes.

You’ll start by just thumb tightening them on. Then you’ll want to install the pedals to 30Nm (22 ft-lbs) of torque, which is basically tighter than you probably normally install pedals. Not breakage tight, but when they feel snug, got a bit more. Technically speaking pedals are designed to will automatically tighten over time as you use them.

Once installed, you’ll crack open the smartphone app, which runs through a two-second calibration process. First, you enter your crank length in (which is normal for all pedal based power meters), and then you’ll do a zero offset with no load (also normal).

  

Then it needs to determine the exact installation ‘angle’ of the spindle. While other pedal based power meters figure this out automatically, SRM has gone with the one-time procedure. Given it only takes a second or two, it’s not a big deal. Simply stick your drive side pointing down, and then tap to confirm:

 

And with that, you’re done.

The SRM X pedal has a claimed weight of 172g per pedal, and my handy-dandy scale seems to confirm that:

 

Ironically, these are actually lighter than the PowerTap P2 pedals for example, which are 200g. Though, they’re heavier than the Garmin Vector 3 (161g/pedal) and Favero Assioma (150g/pedal). Of course, none of that really matters if you really need SPD compatibility, since they don’t offer that.

The claimed q-factor on them is 55mm, which seems the same as my rando pair of Shimano SPD pedals I’ve got floating around here. The Q-Factor is simply the distance from the crank arm to the center of the pedal. Some pedals have to artificially lengthen this to account for electronics.  While some with injuries have reason to worry about q-factor, the reality is most don’t. Your q-factor changes between most bikes. For example your road bike is different than your mountain bike (quite considerably), and that’s also different than an around-town/commuter bike you have. And different yet again to any indoor smart bikes you might be lucky enough to have. In other words – don’t fret it, and certainly not here.

For the above comparison, I’ve placed the tiny LED portion beyond the edge of the wood, because that extends through your crank arm, thus isn’t counted here.

And the stack height is 10.5mm on them, which is from the center of the pedal to the base of the cleat (effectively the underside of your shoe). Since there isn’t an easy way for me to take a photo of that, here’s something similar.

The batteries on them are rechargeable, and use these little contact points to charge them with the two included charging cables. Somewhat oddly however, they don’t include a dual USB charger in the box. While normally I wouldn’t give much thought to that, Favero does include a handy dual-USB charger in the box (and they cost half as much). Plus, the obvious being that you usually charge both pedals at the same time, so now I had to go off and find two wall chargers (yes, I could just steal the Favero one, but that’s not the point).

On the bright side, the length of cable included is crazy long, so it’s easy to just leave your bike on a trainer or somewhere else and run the charging cables to them.

The only downside is they are a bit finicky to get exactly onto the charging contact point, I wish they just snapped to the correct place like the Favero Assioma ones. But once on there, you’ll get the light on the end of the spindle illuminated:

 

Now – for arguably the biggest issue with the SPD X pedals: Battery life.

And things are gonna get messy in this section.

Officially the current website claim is “Up to 30h runtime (standby power draw is 2-5% per day)” – and at first your brain says ‘30 hours’, ok, not spectacular, but basically charging once every 3-6 weeks for most people. Except one problem: That standby claim is what kills ya. That’s 2-5% per day, and I can pretty confidently state it’s definitely closer to 5%/day (and I’ve been using the SRM app to track that). So a week of standby in between rides knocks off 35% right there (7d*5pct = 35% off).  Two weeks brings you down 70% total. Leaving you basically 10 hours of riding time between two weeks.

In other words, you’re gonna charge these a lot. Roughly every two weeks. It took me quite some time to figure this out – and my experience seems to match countless others based on comments people have left, friends of friends, and the TrainerRoad Forums. So while it’s plausible you could do a single 30hour ride on it (not my cup of tea), the reality is for most of us you’re looking at charging every other week.

HOWEVER…….

There’s some good news here soonish. First off, is that through some software battery improvements delivered to units via firmware updates has extended the battery life to 35 hours. But more importantly, turns out my unit from last summer is technically a Gen 1 SRM X set. Whereas what they’ve been producing more recently is a Gen 2 set, which has an improved battery adding another 10 hours of ride time. However, beyond that the company says they’re actively working on another update that’ll essentially eliminate the standby battery burn, down to negligible/normal levels (a fraction of a percent a day).

In any case, once you’re ready to ride you’ll pair it up to your head unit via either ANT+ or Bluetooth Smart.  Both are supported concurrently.  I’ve paired it successfully to pretty much every bike computer and wearable released in the last few years. No issues across the board. For all capable units I’m using ANT+ as the preferred connection type, so you get extra pedaling metrics (but not the official Cycling Dynamics stuffs, more on that in a second).

From an ANT+ standpoint, the unit broadcasts power balance, ANT+ power pedal balance, ANT+ pedal smoothness, and ANT+ torque effectiveness.  Still, here’s a link to a Garmin Connect activity recorded via via ANT+:

Now, there’s actually a toggle within the app for so-called Bluetooth ‘Zwift mode’, which basically tells Zwift how to handle the dual pedals. That’s because despite power meter pedals having been around for just shy of a decade now (and about half of that with Bluetooth), Zwift hasn’t figured out how to implement multi-channel pairing like everyone else. That means it’ll only pair to one side or the other.

 

You can see this in Zwift, first in normal mode where it enumerates both pedals:

And then in Zwift mode, where only the right side SRM pedal shows:

Favero has essentially the same issue with Zwift, though, Garmin has managed to channel the data in correctly so that Zwift isn’t any wiser. Note that we’re not talking about power balance in Zwift (they don’t support that either). Instead, what will happen is that Zwift will only see data from one power meter side, not both. So if your pedals battery power runs out, it can’t gracefully fail over like it can for Vector.

The pedals also support standard zero-offset commands from head units like Garmin, Wahoo, and more (effectively a calibration, but that’s technically a different term/function) . You can perform both via ANT+ or via the smartphone app over Bluetooth Smart, using a compatible head unit to zero-offset your unit.  In general, I do this before every ride, as a quick validation that things are working as expected.

You’ll trigger a calibration just like you would other power meters by going into the ‘Calibration’ comment on your head unit, and by ensuring your drive-side crank arm is at the 3’oclock position (forward).

 

Note that I have seen numerous cases where the left pedal is a bit sleepy upon wake-up. In the SRM system, the right pedal is considered the primary/master, and I often see that it takes a bit longer for the left pedal to slumber awake. As such, while it’s still waking up, it’ll fail a calibration test. Alternatively, you can add the power balance data field to your bike computer, to validate you’re getting power from both sides. Or, you can crack open the smartphone app, as I did yesterday when it was sleepy. Within a minute it had fully woken up and was good to go. Sometimes it’s instant, yesterday it was tired. Not sure why.

Now, if your battery dies mid-ride, it’ll depend on how you’ve paired for whether or not power will continue to broadcast. For ANT+, the pairing happens via the right pedal only. That means you’ll lose all power if you lose the right pedal, but if you lose the left pedal it’ll detect that loss and simply double the right-leg power (and all is basically fine). Whereas in Bluetooth, you’ll pair each side individually, and thus, it’ll actually detect the loss and double the remaining leg’s power. Here’s a little graph from the manual:

Mind you, this specific ANT+ vs Bluetooth failover functionality is purely a function of how SRM has implemented. Other companies, such as 4iiii, do seamless failover on both protocols, so it doesn’t really matter which side you lose.

Finally, within the SRM X smartphone app, they do have a handful of other data pages with more information. For example, you can look at detailed diagnostic information if you want to.

 

Though, I’m not super clear on the lifetime hours here, since I’ve got far more hours on these pedals that that – as I’ve been using this set since last summer on my main road bike. Maybe that’s since last firmware update or something.

There’s also the ability to see power, torque, and balance data in real-time, though, I suspect you won’t actually use this beyond a super quick check:

Finally, for a bit of non-tech stuff. When it comes to adjustability, you can adjust the spring force using a 3mm Allen key, which is done on the rear of each pedal binding:

I didn’t have any issues with tension, durability, or anything else in that realm in using them over the last year. However, I did have issues with balance on the first pair of pedals I tried last Spring (2020), which in turn lead to issues with accuracy. SRM believes that pair was part of an early/initial factory run last January/February (2020) and they since changed a few items that may have caused that issue in first production run units. The unit I’ve been using from summer 2020 till now (March 2021) is also a normal production run unit, but some 6 months later.

Power Meter Accuracy Results:

I’ve long said that if your power meter isn’t accurate, then there’s no point in spending money on one.  Strava can give you estimated power that’s ‘close enough’ for free, so if you’re gonna spend money on something it shouldn’t be a random number generator.  Yet there are certain scenarios/products where a power meter may be less accurate than others, or perhaps it’s got known edge cases that don’t work.  Neither product type is bad – but you just need to know what those use/edge cases are and whether it fits your budget or requirements.

As always, I set out to find that out.  In power meters today, one of the biggest challenges is outdoor conditions.  Generally speaking, indoor conditions are pretty easy to handle, but I still start there nonetheless.  It allows me to dig into areas like low and high cadence, as well as just how clean numbers are at steady-state power outputs.  Whereas outdoors allows me to look into water ingest concerns, temperature and humidity variations, and the all-important road surface aspects (e.g. vibrations).  For reference, SRM has a claimed accuracy rate of +/- 2.0% for the SRM X pedals.

In my testing, I generally use between 2-4 other power meters on the bike at once.  I find this is the best way to validate power meters in real-world conditions.  In the case of most of these tests with the SRM X pedals I was using these other power meters or trainers concurrently over the course of the last year:

4iiii Precision Pro dual (on XX1 crankset on mountain bike)
Elite Direto XR Smart Trainer
Elite TUO Smart Trainer
Quarq DZERO (SRAM crankset on road bike)
Quarq DZero (XX1 crankset on MTB)
PowerTap G3 hub (road bike)
Tacx NEO 2T Smart Trainer
Wahoo KICKR V5 Smart Trainer

There’s undoubtedly other trainers that aren’t top of mind right now, but basically since this has been mostly on my road bike since last February, it’s pretty much been on every trainer I’ve tested since last February (and, you can see that data in most of my trainer reviews over the last year).

And just in case it’s not easily noticed, I’m testing across two bikes, both my road and mountain bike.

First, let’s look at a Zwift Ride compared to a Quarq DZero and a Tacx NEO 2T. This was on a looped course, with a solid sprint thrown in each loop. Otherwise, the power hovered in the ~300ish watts range, as I was on a group-ride, so you see the constant shifting staying with the group. Here’s that data set:

Overall, the numbers are very close actually. In theory you’d want the SRM X pedals to be highest, and the Tacx NEO 2T to be lowest, and the Quarq to be slightly below the SRM X (due to the way drivetrain losses are handled). Though practically speaking once you account for the variances in claimed accuracy rates, in some cases it ends up being a wash – like in this case. So let’s zoom into a few chunks.

Here’s a steady-state section, followed by a 950w sprint, followed by steady state again. Notably, the below chart has *no* smoothing applied. As any regular connoisseur of power meter data might know, that tight alignment between three power meters on a 950w sprint is actually somewhat rare and incredible. Seriously, you rarely see data this close from three sources – especially across sprints.

And the same is true if I look at all the remaining sprints. However, let’s zoom back out a bit – and I want you to notice the green line that I’ve highlighted, seemingly dipping a bit here and there:

Curiously, I then scrolled down in the data set, and you can see that each of those yellow dips below, aligns to a dropout of the left side, seen in the graph below. Essentially, there’s a connectivity issue between the left side and the right side.

And this is an example of what happens when the battery starts to get low – you see these slight connectivity issues like this. Brief drops for a split second. Or literally, actually just one second.

However, I then went back and pulled set after set after set of trainer rides, to see if I could find examples of this elsewhere, and couldn’t. So it’s fairly rare. Not here in this Zwift ride:

Nor this ride:

Or this ride:

Or this ride (note – the color changed on this one, green here is the Elite Tuo, the SRM X in purple matches beautifully to the Quarq & PowerTap G3 hub).

In fact, while we could dive into the nuances of all those rides, they all tell the same story – near perfect alignment with the pile of other power meters and trainers I’ve been using. Those rides date back as far as September, and I’ve included them to illustrate some of the longevity here. Also, I’ve got the data, might as well flaunt it I guess. Otherwise it just goes to waist sitting on the DCR Analyzer – never getting its moment in the sun.

However, there is a singular ride that’s an exception to this rule, from last month. This was a TrainerRoad ride with one minute intervals and then some longer steady state intervals. Here’s that data:

What you see here is sorta two stories.  Initially, during the warm-up, things seem mostly fine. A touch low, but not overly concerning yet. However, during the work interval for all of the 60-second intervals, the SRM X seemingly undershoots every single interval. Yet later in the back half of the ride, it seems more or less fine (a hair low, but not overly concerning).

However, this is where on a dual-sided power meter, you can quickly suss out what’s likely going on. And all one needs to do is look at the left/right data. And you can see quite clearly that the right side pedal is readying substantially lower on each of those sets. As to why, that’s anyone’s guess. Is it a temp compensation thing? Unlikely – since this was in the middle of a snowstorm, and the bike had been in the exact same spot for weeks. Is it just a bad offset on that side? Perhaps, but that doesn’t explain why it stabilizes later.

Given this is the only example I can find of it in piles and piles of data (including other short interval workouts), I’m not overly concerned about it. But I figured I’d mention it.

So, let’s finally go outside. Here’s one of my usual test loops outdoors. It’s mostly good quality roads, but it’s also got some nice long brick sections too, just to see how it handles vibrations. This is compared against a PowerTap G3 hub and a Quarq DZero power meter. Here’s that data:

As we can see, the data is fairly close together, with the PowerTap hub properly below the others – further down the drivetrain, as expected.

Here’s some steady-state riding, followed by a lazy sprint. Unlike the earlier crazy-close indoors sprints, this one shows a bit more normalcy and separation between them. That’s common due to slightly different transmission rates and alignment of the data on multiple head units.

Since we haven’t done so yet, let’s take a quick look at cadence. There’s no cadence magnet installation here, it just does it all internally. And all seems well here. All of these agree as long as I’m pedaling:

We see a slight bit of difference in how they handle brief soft pedaling moments. If I remove the smoothing entirely, you can see each of the three units interprets my soft pedaling slightly differently:

It appears the SRM X goes a bit lower than the others, though I’m not sure if there’s any real-world difference between it calculating my soft-pedaling at 35 vs 40 rpm. The second I apply normal pressure, you see all three instantly agree again.

If we look at the power curve for this ride, we see the SRM & Quarq pretty close, with the PowerTap G3 lower. Perhaps a bit lower than I’d prefer by a few watts, but maybe my drivechain was exceptionally dirty that day or something.

Next, another outside road ride, before we go off-road. In this one, the SRM X s the line labeled ‘Wahoo RIVAL’, in blue (compared to a Quarq DZero and a PowerTap G3). Here’s that data set:

I’m not gonna hash through the above one again, because frankly it’s boring and spot on. Cadence looks spot on too:

And the power curve looks beautiful too:

Next, let’s head off-road. Now, living in the Netherlands there’s only so much variety in off-road terrain – and none of it is crazy rocky. I would have loved nothing more than to give you piles and piles of off-road rocky data. But alas, with current travel restrictions, that’s simply not possible. Thus, you get more rooty than rocky, for my mountain biking.

First, some loops around a local cyclocross circuit. In this case I have comparative data to a Quarq XX1 DZero power meter, as well as a 4iiii Precision Pro dual-sided crankset. However, the last few rides I’m having some sort of battery or connectivity issue I’m troubleshooting on the 4iiii, so we’re gonna toggle off that data because the drop-outs skew everything. I think I’m close to solving it (pretty sure it’s the battery caps).

Now, if you’ve ever looked at mountain bike or cyclocross power data, you’d know it’s largely a jumbled mess. Sure, if you’re climbing on a mountain bike for 30 minutes – that’s easy and clean to look at. But given the largest climb I have around here is approximately 57 seconds, that’s not the kinda data you’re gonna see. This is:

Now for this ride I had just moved the pedals to the bike – and in deed, you see that first 20ish minutes or so the green line of the SRM X is notably different than the Quarq. While I had done some settling sprints before the ride, you can see it’s clearly still settling a bit. But as the ride goes on, the two get closer and closer together…except when they’re not.

And that’s the challenge with only two power meters (and why I have a third on there), it’s just hard to know who is right. Let’s look at this section here. Mind you, I’ve smoothed this at an astounding 20-second smoothing rate, just so you can make some sense out of it.

This is without smoothing, and what it actually looks like:

And ironically, this is the rare scenario where the unsmoothed data makes it slightly easier to see what’s going on. In a nutshell, both units are actually very very close, but the Quarq appears to spike slightly higher each time to a surge than the SRM X. Response time is near identical, but the Quarq believes (perhaps correctly, I have no idea) that these surges are a bit higher. And since the surges are substantial – 700 to 900w, that skews the data considerably more once smoothed.

Typically speaking when looking at power meter data and very short duration surges in that 700w+ range, you’re going to see differences there. These surges only last 1-3 seconds. So the averaging and 1-3 second differences is actually really screwing up that smoothed chart. So much so that I don’t think we’re looking at an inaccuracy issue per se, but rather the complexity of this type of riding and how different brands decide to deal with smoothing (all brands have to smooth to some extent, where they draw the line is what matters).

So let’s look at another off-road mountain bike ride – this one from yesterday. Again, the same surge and punchy trails that I have access to. Very rarely are there long and stable sections. Here’s that data:

And again, above smoothed at 20-seconds, we see the same thing – the Quarq appears to be consistently higher and above the SRM X, even for some longer duration stretches. For this ride, calibration was done after the bike had cooled for about 15 minutes outside, and then again about 24 minutes into the ride. Here’s a section right after that second calibration, first with smoothing:

And then without:

Umm…yeah. Good luck with that data.

Essentially, it’s just like above – the Quarq appears to shoot higher than the SRM X in most of the quick punches.

But wait…let’s pull that 4iiii data back in. In this case, as part of my battery cap troubleshooting, I actually pulled the battery on one side, letting it run as a single-sided unit. That cleaned up the dropouts, and gives me a third source (albeit single leg only). Still, it’s something I guess:

It seems to align more closely to the SRM than the Quarq, but again, it’s just doubling a single leg, and thus you’ll see less accuracy in that method.

All of which is to say, off-road power meter data is really hard to analyze from an accuracy standpoint – especially punchiness. Each brand has to apply considerably more data processing to sort out bad data from good data, effectively trying to figure out if that spike in data is your surging around a corner, or just the impact of a rock/root/whatever on the pedal, or a big drop. And it appears based on the data that I have, that SRM is applying a bit more smoothing off-road, thus minimizing the spikes slightly more and making it appear lower than the Quarq.

Overall, based on what I see, the SRM X pedals are super accurate on road and indoors, with only a single ride in the last 7 months or so that isn’t perfect. Same goes for cadence data. Once you venture off-road, it appears that the SRM X is mirroring the Quarq and 4iiii, however, applying a bit more smoothing than Quarq is – which tops off some of the brief 1-2 second surges.

(Note: All of the charts in these accuracy sections were created using the DCR Analyzer tool.  It allows you to compare power meters/trainers, heart rate, cadence, speed/pace, GPS tracks and plenty more. You can use it as well for your own gadget comparisons, more details here.)

Summary:

The SRM X pedals are notable for a few things. First, they’re the only pre-built SPD power meter option on the market today. While you can DIY marriage yourself a pair of Favero Assioma pedals with SPD pedal bodies, that does require some how-to, and the understanding that you’re voiding your warranty (and likely modifying your shoes too). Second, they’re notable because this is SRM’s tech, and not Look’s – thus they don’t follow the same fiasco that was the SRM EXAXT road pedals which required super finicky installation and were generally a mess to get accurate. Whereas with these SRM X pedals, the installation takes mere seconds, doesn’t require special tools, and ultimately the accuracy ‘just works’.

Of course, getting ahold of the pedals is tricky. They’ve mostly been out of stock on both sides of the pond for quite some time. Shipments are of course going out, but basically to people on a waiting list. They’re priced at $1199USD/1190EUR (including VAT), which is expensive – but honestly, given there’s no other options on the market today, it’s what I’d expect. A pair of road-focused Garmin Vector 3 pedals is $999, and that’s roughly where the PowerTap P2 pedals were sold up till they were discontinued last month. Of course, Favero is considerably lower for their dual-sided solution, but that’s road-focused unless you want to roll your own SPD pedal install. So while the $1,199 price is high, I do think it’s fair for an easy to use and more durable mountain bike pedal (which can also be used for road, if you wish). Note that I reached out to SRM today, and they noted that they recently brought online a second production line and facility in Italy, and are ramping up production there.

Now, the main downside to the SRM X is clearly the battery life aspects. Mainly the standby battery burn. Upwards of 5%/day in standby. Meaning you’ll burn through 1/3rd of your battery each week. And with only 30 hours to begin with (optimally), that’s a lot of charging. However, it does sound like this will be remedied to more acceptable levels in upcoming hardware updates, which should get rid of the standby issue entirely, while also boosting ride time battery life.

Ultimately, I’d like to see SRM continue down this power meter path. Namely because I think if they can solve the stock/supply issues, it represents a viable product segment for them – especially if they expand beyond just and SPD pedal, and perhaps look at other pedal types. Certainly that’s what SRM EXAKT on Look KEO is for in theory, but in execution – not so much. And finally, while SRM has mostly lost the crankset power meter market due to their pricing, the SRM X is actually reasonably priced relative to the market options – thus, it’s also a trend I’d like to see continue.

With that – thanks for reading!