Stages SB20 Smart Bike Indoor Trainer

The Stages SB20 is a solidly built, good quality smart bike with lots going for it. Overall it outperforms the Wattbike Atom, which is the bike it's most directly competing with. It's at the expensive end of the market for true smart bikes, and it's not quite as accomplished as some of the others out there, but overall it's a very good option for heavy use indoors.

If you're a cyclist, you'll probably know Stages because it makes crank-based power meters. But for most of the rest of the world, Stages is a company that makes spin bikes for gym bunnies.

The SB20 is basically the meeting of those two worlds: it's the Stages crank power tech built into a frame that's based on the company's SC range of gym bikes, with the dumb spin transmission replaced by an electromagnetic resistance unit acting on a huge 23kg flywheel, driven by a quiet and reliable Gates carbon belt.

The SB20 offers up to 2,200W of resistance, which should be plenty unless you regularly win on the track sprint circuit, and gearing is virtual, and configurable to your preference. More on that in a bit.

The SB20 is designed for heavy use indoors with a smart training app, and plenty of thought has gone into making it ideal for that. You can charge your phone or tablet via USB while you're riding, and there's a phone tray and an optional iPad holder supplied. There are two water bottle holders either side of the bike which will accept pretty much any bottle, so you're not limited to bike bidons – you can use your gym bottle if you like. The bike is ANT+ and Bluetooth compatible, so it'll work with anything you're likely to be running a training app on.

It's a reassuringly solid thing, the SB20. Don't, under any circumstances, attempt to move the 70kg box by yourself, unless you want a hernia. Once it's out of the box and assembled, which is surprisingly easy, it's not that difficult to manoeuvre on its two skate wheels, but if you need to lift it into position or up any stairs, make sure you've got a burly friend to hand.

Like all smart bikes, one of the great things about having a static rig like this is the adjustability. You can change everything here: saddle height and offset, stack, reach, crank length... you can even swap out the bars if you like.

This is great news if there's more than one person in your household who wants to use the bike; assuming you can both get on with the same crank length (moving pedals is a faff), the other tweaks can be done in less than a minute, especially if you've made a note of the settings. It might take you a few goes to get it dialled in, but once you do the setup is easily repeatable.

I mentioned before that the SB20 uses Stages' crank-based power technology. It's the Stages Gen 3 dual-sided power meter, which delivers +/- 1.5% accuracy and is relied on by a number of WorldTour pro teams.

This is in one sense good, as it's well proven at WorldTour level and is well-developed and reliable. It's less good in another sense though: the two power meters run on their own 2032 coin cells, like they would on your bike. That means that even though you're plugging the bike into the mains for the electromagnetic resistance, you'll still be faffing about replacing the power meter batteries from time to time. Generally they're good for around 100 hours, which if you're keen is only going to be a few months. It's not a deal breaker, but you just know they're going to go on the blink before (or in the middle of) that important Zwift race you've been working up to.

Workout workings out

Okay, let's have a look at some numbers. Here's a plot of a power benchmarking workout I often do, because it covers a lot of my cycling power range and you can also change a couple of other variables along the way, and see how ERG mode works. I was benchmarking the SB20 against Garmin's Rally 200 double-sided pedals, which I've found to be accurate and reliable over a range of these tests.

Firstly, and most obviously: the SB20 is doing a good job here. For this test the bike is reading slightly under the pedals (212W vs 219W), whereas for other rides that have been at a higher intensity (races, for example) the Stages bike read above the pedals and not below. You can see that it does both here, at different points in the ride, but generally the blue line is slightly under the purple one.

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At intensities around 100% FTP, the two power meters agree most closely. The first three intervals after the warm-up are 110-130% of my FTP, and the difference between the two traces is only about 3W here. As you go further up the intensity scale the gap tends to increase: when we get to the two sprints at the end (225% and 250%) the gap between the two is about 10%, whereas in the FTP zone it's more like 1%.

The two power meters respond differently to standing efforts, too. Intervals two and four are standing, and the lines diverge a bit more there, with the discrepancy more like 3%. Because I'm cycling at a lower cadence it may be down to the sampling rate of the different power meters, or more likely they just respond differently to a less even pedal stroke, which is what you get when you stand up.

And which is right? Impossible to say, really. I'd have no issues with either of these power traces independent of the other, and the differences are quite subtle. Neither of them are exactly right, and both of them are close enough. The numbers I was seeing made me competitive with the people I'd be competitive with outdoors, so they're entirely believable.

I ran this test in ERG mode, where the trainer tries to adjust the resistance to output the correct power based on your cadence. I wouldn't say that the SB20 is especially good at this, compared to its direct rivals and other direct drive trainers I've used. Here are some reasons why.

When you're riding at a constant cadence the SB20 doesn't (generally) fall into the trap of increasing the resistance too far, and then dialling it back, which results in a power spike at the front of each interval. That's good, but it goes a bit far the other way. The ramp up is too slow, so when you're doing something like a 10-second sprint effort you generally don't make it up to the target power. The last spike on the graph is a 675W effort on paper, but I didn't even make it to 600W before the interval was over. That was common. Also, it's not like the bike adjusts more slowly to make sure it gets it right, and then sits there: you still get a fair bit of variation in the power.

Ending high-power intervals and moving to low-power recovery is another thing that the SB20 seems to have some issues with. It often takes a while for the resistance to drop, and then when it does it drops too far. This is especially noticeable in the second interval here, when the bike held onto the interval for at least five seconds too long, then dropped the power all the way down to about 50W before ramping it back up again to the recovery level of 145W. The Stages bike consistently had problems with high to low power. Or, rather, it inconsistently had problems with it, which is worse.

Overall, the ERG experience wasn't that great, really. Compare that trace to the same workout performed on a Saris H3, which is about the best ERG trainer at the moment. Zwift gives you a star for every power interval it reckons you hit. The H3 scored 21/21, every time. The SB20 was normally around 15/21.

Moving away from ERG mode, if you're riding around in Zwift/RGT/Rouvy then there are two other ways to affect the resistance. On the one hand, the gradient changes in whatever virtual world you're exploring will be relayed to the bike and the resistance will change accordingly. On the other hand, there are shift buttons on the levers that allow you to change the resistance manually, just like changing gear. There are three buttons on each lever, and when you've got the bike hooked up to the Stages Link app on your phone you can assign different functions to them.

There are a whole bunch of standard setups available through the app, with both single and double chainring transmissions mimicked. You can also choose to use Dream Drive, which gives you a sequential setup with up to 50 gears. I tried out a few and ended up going with Dream Drive with 20 gears, as that gave decent jumps between the gears and was easy to remember: right hand buttons to make it harder, left hand buttons to make it easier. For me the buttons aren't spaced widely enough to be distinct, so having upshift and downshift next to each other on one lever led to a lot of mis-shifting, especially in sprints where grabbing the hood can accidentally press them. They're all just a bit small and close together.

The gear change itself is decent enough; it's not the realistic clunk that you get on the Tacx Neo Bike Smart and it's not quite as good as the Wahoo Kickr Bike either, but it's faster than the Wattbike and pretty easy to get used to. There's no screen to tell you what gear you're in, so if you want that information you'll need to pair with the Stages Link app on your phone, which is fine if you don't also want to use your phone to run Zwift Companion. I ended up running two phones, one for each. You get the same kind of issue with the Wattbike Atom; both the Kickr and the Neo bikes have a gear display, although one (the Kickr's) is bad and the other (the Neo's) is good.

Stages makes big play of the size of the freewheel on the SB20 (22.5kg) and how it gives an 'incredibly realistic feel when climbing, accelerating and coasting'. That's fair: the ride feel of the SB20 is pretty good all round. I found that it was a bit easy to wind up on flat sprints compared to my usual trainer, a Tacx Neo 2, and that made sprinting quite a high cadence effort, but overall I was really happy with the experience of being on board the SB20. It's quiet, and solid, and easy to settle into for longer indoor efforts.

Is it 'the only bike that can deliver the realistic inertia of outdoor riding', like Stages claims? Not really, no. Having ridden all of the main static smart bikes now, I'd put the ride feel of the SB20 more or less on a par with the Wahoo Kickr Bike, and it's better than the Wattbike Atom, but for me the Tacx Neo Bike Smart is still the best in terms of its ride quality. It's still, for me, the one to beat overall, too. It comes with daft weedy fans that are pointless, but nearly everything else is on point: excellent ride feel, solid frame, great adjustability, useful display.

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At full retail the SB20 is £500 more than the Tacx, and at that price I wouldn't consider it. But realistically you can find both of those bikes and the Wattbike Atom for around the same money, with the more complicated Kickr Bike costing considerably more.

Conclusion

Like any static smart bike, the Stages SB20 makes a lot of sense if you're going to put a lot of miles into your legs indoors, and especially if more than one person wants to ride. The SB20's main plus points are the super-solid build, the quiet running and the accurate power numbers. For me it's not best in class – the ERG performance was a bit disappointing, and there are a few hardware niggles too – but it's still a very good option for high-volume indoor training.

Note: The original value score and conclusions were made based on the rrp at the time, and the Stages SB20 is currently discounted to £1,699.

Verdict

Solid, quiet and accurate indoor trainer for high-volume riders