The all-new Powerfly FS 9 shares a lot in common with the EX trail bike, but the addition of a Bosch pedal-assist motor turns it into quite a different proposition. It’s not quite perfect but the combination of a well thought out chassis and chubby rubber mean it’s capable of some quite amazing feats.
Trek Powerfly FS 9 Plus highlights
- 130mm front and rear travel
- Adjustable geometry
- Boost axle spacing
- 250W Bosch pedal-assist motor
- SRAM EX e-MTB-specific groupset
The bike gets 130mm of travel at either end, using Trek’s ABP design, which uses a concentric pivot at the dropout to help isolate brake forces from bump forces. On an e-bike, where the extra weight means being able to stop in good order is even more critical than usual, this is a very welcome feature. The Mino Link geometry adjusting chips in the seatstays are also present and correct, allowing a 5mm bottom bracket drop and 0.5deg off the head angle from the ‘High’ position figures of 338mm and 67.4deg respectively.
As you’d expect from the people that invented it, you get Boost axle spacing at either end to help stiffen up the 40mm wide 27.5 rims shod in 2.8in rubber. A new feature to the bike is the Knock Block, which uses a system of keyed stem spacers and a special headset cap to limit steering lock and prevent the bars from hitting the top tube.
The system also means that Trek could use a straighter and therefore lighter down tube without fear of the fork crown contacting it. The FS doesn’t get the clever RE:Aktiv shock technology that the 150mm travel Powerfly LT gets, but it still has a bang-up-to-date metric-sized RockShox Deluxe RT3 shock with a trunnion mount.
The pulsing heart of the bike is a Bosch Performance CX pedal-assist motor pumping out up to 250W of extra go paired to a 500Wh battery that’s mounted conventionally on the down tube. Trek has added a custom bash plate to help protect the motor from damage, a feature first seen on the old Powerfly FS. It retains the integrated bottle opener too, so whether you’re going for mid ride picnic or post ride beer, you’ll not be left wanting on that count.
On this range-topping model, you get the new Intuvia Performance controller, which does away with the bulky stem-mounted display of the plain Intuvia unit and instead gives you a bar remote with small LCD display. It’s much less vulnerable to damage and the buttons have also been redesigned to make them less likely to be accidentally triggered when riding.
Cycling through different display modes requires you to press and hold the power mode button, which can lead to you dropping into a lower setting until you get the knack of it, but once you’ve twigged it’s simple enough to move between range remaining, trip distance and total distant. Speed is permanently displayed and it’ll flash up which assistance mode you’re in as and when you change between them.
Our test loop on this bike consisted of a 42km trip in the Swiss Alps around Flims, taking in a fairly substantial 2,200m of climbing. Trek is keen to push the adventuring potential of this bike and the ride certainly showed that. To attempt it un-assisted would require a very long day out and a lot of fitness.
The route took in some climbs that would have been simply soul destroying, but that the Powerfly breezed up. As a range extender this bike – and e-MTBs in general – can open up a lot of riding to a lot of people.
It also softens the mental blow of having to do on-road descending or unrewarding sections of trail to create a circular loop. I’ve no doubt that if it’d ridden up all the climbs under my own steam, I’d have spat the dummy on certain parts of the loop. However, as I’d not had to truly earn all the height, it was much easier to be more laissez faire with losing altitude.
These benefits make it ideal for exploring new mountain terrain, where taking a wrong turn or an unknown path might turn into quite the ordeal on a normal bike but is simply an easily corrected error or entertaining diversion when there’s a motor to help you back up.
In common with all pedal-assist bikes, it’s not a completely effortless experience however. In order to nurse the battery round a route that did very little in the way of contouring, I rode most of it in the Eco or Tour modes and got a fair old workout in the process.
With the odd burst of Sport mode to get me up super steep and technical sections, I finished the ride with a couple of bars of battery left, though heavier riders and those that were more aggressive with their assistance settings cut it much finer on their reserves.
I’m 5ft 8in / 173cm tall and chose the 19.5in frame size – equivalent to a Large – as I prefer a longer bike. With a 473mm reach, it was decently spacious and the relaxed head angle relative to the travel was welcome on steeper terrain.
The bulk of the bike also adds to this feeling of stability and the fat tyres really help too. Getting tyre pressures right on a plus bike is always critical, with a very narrow window to hit the balance of squirm versus grip. Add in a load of extra weight and some pretty rough trails and this is even more critical.
Though the tubeless ready Chupacabra 2.8in tyres used Bontrager’s reinforced Inner Peace sidewall, with a long ride and limited access to spares, I rode them at a higher than ideal pressure to ensure a puncture free day, which meant the bike's full monster truck ability was slightly muted.
With more time to get the pressure dialled, I’ve no doubt that a compromise could be found, though the tyre’s low-profile shoulder tread would still be a limiting factor when it comes to how hard you could carve a corner. Given that rolling resistance isn’t as much of a factor on an e-bike, I’d rather see much more aggressive tyres and accept that I might get a few kilometres less range.
That said, the Powerfly FS is a much more capable descender than the travel figures suggest, with the Pike fork up front staying solid under hard braking and both ends of the bike shrugging off some fairly wild terrain. The Avid Guide brakes gave plenty of bite, with a 200mm rotor up front and a 180mm one out back.
At a relatively lightweight 62kg I did manage to get enough heat into them on one flat-out descent to make the lever start to fade and heavier riders ended up with rotors that were quite literally smoking hot, though this was through fairly extreme use.
One area where I wasn’t totally convinced was the SRAM EX1 drivetrain, which was developed in conjunction with Bosch to work with its motors. It’s an eight speed transmission, with an 11-48t gear range on a cassette that fits onto a conventional, non XD freehub.
It does shift much more cleanly under the extra load of an e-bike than other drivetrains I’ve tried, but there where quite a few occasions where the cadence that I wanted to turn left me hunting between gears in the middle of the block. The range on offer is very welcome however, and it’s absolutely ridiculous what the bike will haul you up, as long as you keep the faith – and the pedals turning.
The shifter does only allow you to drop one gear at a time, so until I’d wrapped my head around this and got back into the habit of clicking down multiple times, I did find myself stalled out when I’d failed to anticipate upcoming changes in gradient.
In totality, the Powerfly FS is very impressive and definitely builds on the old bike, undoubtedly thanks to the fact that it’s been developed in parallel with Trek’s new mountain bike range rather than as a distinct model line. As a tool to get out and explore new terrain as well as a toy to keep you entertained, it’s mighty impressive, with well mannered handling and a nicely featured frame.
I’d prefer beefier, more aggressive tyres to really maximise the downhill confidence as the extra weight isn’t really an issue on a bike like this. In a similar vein, I’d also been keep to reserve full judgement until I’ve ridden its longer travel brother to see whether there are any real drawbacks to bringing a cannon to a knife fight.