There’s a lot to like about a belt drive on a city or leisure bike. You get silent operation, there’s basically no maintenance, and they last more or less forever. Once it’s set up and running smoothly, you probably won’t ever need to think about it. The main downside until now has been how to integrate that belt into an e-bike with a rear hub motor. You can’t use a derailleur, so you’re stuck with a single gear, and that can limit the appeal of a bike, especially if you live in a city where hills are an everyday part of your life.
However, there is a new range of automatic shifting, planetary-gear motors which is helping to make belt-drive, hub-gear bikes suitable for a much wider range of terrain. Bikes like the estarli e28.X, which has an automatic three-speed motor hub built in, are helping to bring the simplicity of the belt drive to a wider audience than ever.
How do automatic gears work?
The estarli e28.X is a clever bit of kit. At its heart is a 250W, 50Nm Estarli Cycle Systems hub motor transmission, giving you plenty of power for your e-bike adventures. It uses a torque sensor to match the motor output to your effort but instead of supplying the power directly to the road, there’s a three-speed gearbox in the power train. When you’re stopped the hub will automatically reset to the lowest gear, which makes it as easy as possible to get going. Once you start moving, the increase in speed means that centrifugal forces build in the hub, and at two predefined speeds (about 13km/h and 20km/h) the forces move internal parts of the hub into a different position and automatically change to a higher gear. So as you build up the speed, you automatically move up through the gears. And when your speed falls, those internal bits fall back again to move you back to a lower gear for the slower stuff.
There’s a lot to like about a system like this. For a start it allows you to use the maintenance-free belt drive with a hub gear without the limitation of a single gear. Also everything’s contained within the hub, so there’s nothing exposed to the weather, and nothing to knock out of whack, a perennial issue with derailleur systems. And lastly, it’s lovely and clean. The estarli e28.X is a very clean-looking bike anyway, with fully-internal brake hose routing, but there’s no need for a shifter or shift cable with the automatic hub so that’s one less thing to route through the frame, or take up space on your bars.
The acid test: the hills of Bath
I’d rate my commute to the road.cc offices and back as, in the grand scheme of things, fairly challenging. On the way home, anyway! My house is right on the outskirts of the Bath (handy for escaping into the countryside) and 150 vertical metres above the city centre. It’s only about 4km, but that’s a decent effort under your own steam. In the unlikely event that the Tour de France ever came through Bath and past my house, it’d qualify as a categorised climb, and at its steepest the gradient gets into double digits. I’ve ridden the climb hundreds of times, on a huge selection of bikes – everything from a lightweight race bike to an electric cargo bike – so I have plenty to compare the estarli to. Not every e-bike has made it easy!
Starting off: the flat bit
Out from the office and across the river things are nice and flat, and so it’s pretty easy riding; certainly I didn’t feel like I needed more than the second of the five levels of assistance that the e28.X offers. It’s a bit stop-start, though: there are junctions, and lights, and of course plenty of traffic. The automatic hub makes navigating all that as simple as possible. If you’ve used a derailleur-geared bike you’ve no doubt experienced the issue of getting caught at a red light, or having to brake suddenly in traffic, and then being in the wrong gear to get going again. That’s no longer a problem with an automatic system: every time you stop or you’re slowed down, the hub automatically clicks back down to the lowest ratio to help you get going again. It’s a real game-changer when you’re navigating in traffic: you never have to think about whether you’re in the right gear because the motor is doing the thinking for you.
The first slopes: learning the ropes
As the road starts to kick up it’s time to up the assistance from the handlebar remote and settle into the climb. It’s another scorching day in the city so I’m looking for maximum help to make sure I don’t arrive at the top of the hill a sweaty mess. There’s plenty of power available from the 50Nm motor, but as the gradient increases you naturally start to slow down. At this point you need to practice the downshift to keep yourself in the right gear. “Wait a minute!,” I can hear you saying. “I thought it was automatic?”
Well, it is, but keeping a constant pressure on the pedals will keep the bits that move locked into place, so you just need to ease off momentarily to allow the motor to click back down to a lower ratio. And remember that the shift points are set speeds, so a quick glance down at the High-definition TFT display on the e28.X will tell you whether it’s time to shift down. After a while, it’s second nature.
Take it easy to make it easy!
Once the road really starts to ramp up you want to keep your effort to a minimum, especially on a hot day. That means cranking the assistance up to the highest mode, and also – and maybe a bit counterintuitively – taking it easy. Even on a 10% slope that first shift speed at 12km/h isn’t difficult to attain, so you just need to relax into the climb and let the bike do the work. A peek at the display will let you know if the hub’s about to shift up, and after a while with the bike you become tuned in to those shift points. Even if you do accidentally shift into the next gear it’s a moment’s work to ease off and get back into the easiest gear.
And is it enough power to get you up to the top without arriving in a puddle? It sure is. Even on a 30°C-plus day I was happy all the way up the climb, and it helps that the e28.X is nice and light, too. I wasn’t always moving fast, but that’s the point: tailoring your climb to the way the hub works is the way to get the best out of it, and there’s plenty of power to get you to the top.
A great bike built around a useful hub
Of course, all that hub technology isn’t going to mean much if it’s built into a bike you can’t get on with, so the good news is that the estarli e28.X is a bike we’ve really enjoyed riding. We’ve recently reviewed this version of the bike on ebiketips and Reviewer Tony Tompkins was a fan: he called it “A low-maintenance urban commuter that’s enjoyable, practical and exceptionally easy to live with.”
Back in 2024 ebiketips editor Alex also reviewed the two-speed version of the bike and scored very highly: it was good enough to be a finalist in our 2024/25 ebikes of the year and it was a significant quality upgrade over the previous bike. All the brake hoses and motor control cables are run internally, and so it’s a very clean-looking bike with classic lines. You get high-quality kit for commuting and leisure riding in all weathers too: quality metal mudguards, integrated lighting, and hydraulic disc brakes. The big tyres soak up city potholes easily, and they’re capable enough to leave the tarmac too if you want to get a bit more adventurous.
The single frame size will accommodate riders from 5ft (1.52m) to 6ft 4in (1.93m) thanks to an adjustable stem at the front and plenty of seatpost range at the back, and the 360Wh downtube-mounted battery is good for up to 90km, depending on where you ride. Alex said in his review that the e28.X that “the sheer get-on-and-ride simplicity of the Estarli e28.X will make it the perfect bike for a lot of people.”
For more on the estarli e28.X, and to see the rest of the company’s range, head over to the estarli website.