HPS Domestique Watt Assist Pro, the world’s lightest e-bike
In general, e-bikes are obviously e-bikes. Large chunky tubes, batteries, crank-based motors, or specific rear hubs often show the bike’s extra potential. The Scott Addict eRide and Colnago E64 are perhaps the closest to a normal-looking (whatever normal is) road bike in the e-bike market today.
Personally, the additional weight and restricted choice of either wheels or cranks have been marks against the current crop of e-bikes in my book.
Story Highlights
- What it is: HPS e-bike that rides and looks like a standard bike.
- Key features: Handcrafted carbon fibre frame, with an integrated e-bike system offering a continuous 200 W of assistance.
- Weight: 9.5 kg + battery (20.9 lb, size 56cm, with pedals)
- Price: €12,000
- Highs: Makes going uphill fun, an e-bike for road bike connoisseurs.
- Lows: Price, cable routing, and rattling.
Perhaps naively, these factors have been all the evidence I needed to be confident that mechanical doping has not been a significant issue in professional racing.
We all knew deep down in our hearts that e-bike systems would eventually become more integrated, smaller, lighter and in general, just less visible. It seems that time has come.
High Performance Systems (HPS) is an Irish brand that has spent the better part of the last decade refining an integrated e-bike system it claims is the lightest in the world. The initial intention was to develop and prove the system, before licensing it to bike manufacturers to use in their bikes.
While developing the system and working with manufacturers, HPS had test frames explicitly designed to house the e-bike system. While the system was progressing at pace, HPS met a fork in the road. Should it continue trying to meet manufacturers’ many demands, or focus on developing the test frames into a finished product?
HPS decided on the latter option, and the result is the Domestique. The word “domestique” is synonymous with pro racing and translates to “servant”. A domestique’s role within a team is to assist their leader during a bike race, and as such is a fitting name for an e-bike, given the assistance it offers a rider.
Watt Assist Pro
HPS was specifically focused on system integration and weight reduction. This was not solely an attempt to hide the bike’s performance-enhancing possibilities from unassuming training partners, as I first assumed, but rather a direct result of the company’s overarching goal: “to offer a high-end road bicycle with an electric motor that behaves and weighs like an unassisted road bike.”
To achieve this goal, HPS turned to Formula 1 technology and engineers to develop the Watt Assist Pro e-bike system it claims is the lightest in the world. It has a claimed weight of just 1.5 kg, including the 85 Wh battery. HPS then placed the system within a custom handcrafted carbon fibre frame, precisely located above the bottom bracket in the seat tube and the down tube. The system’s precision location is said to better harness the lightweight system’s power, offer comparable ride quality due to the lower centre of gravity, and ensure the reliability of the system.
HPS claims the system can deliver up to 230 W of peak power and a sustained 200 W with a maximum 20 Nm of torque. To power this motor HPS offers two battery options, both disguised to look like a water bottle and both of which attach to the bike via a custom bottle cage. The 193 Wh battery is said to provide up to three hours of pedal assistance and weighs 1.2 kg. The smaller 85 Wh battery offers 1.5 hours of assistance, weighs in at 720 g and is the first e-bike battery legally compliant for air travel.
Two buttons located just below the brake levers provide the rider with control of the system. The buttons are integrated beneath the bar tape and are easily accessible from the standard riding position. However, I did feel they could be smaller or even integrated into the lever hood of an electronic groupset.
The system wirelessly connects to GPS head units to provide a visual indication of the active assistance mode. With six separate assistance levels in “peloton” mode and three in “attack” mode, the visual reminder is a welcome addition. The integration into a head unit is also a welcome addition, as all other e-bikes I have ridden either have an extra control unit on the handlebars or a button on the top tube.
The frame
The frame itself is a tube-to-tube construction, custom-designed and manufactured specifically to house the Watt Assist system. In keeping with the traditional sounding “Domestique” name, the frame features classic-looking round tubes and a rich fade effect colour scheme which will only be available on the initial launch edition model as tested.
Perhaps the most striking element of the frame is the addition of a tube connecting the seat tube and down tube. I initially assumed this adds structural rigidity to the frame and was a requirement of the integrated motor. The actual function of the tube is somewhat less complicated. The tube provides a safe passage for the wiring from the electronics unit in the down tube to the motor in the seat tube, while also adding a unique styling feature.
The test model I have is the 56 cm offering. With 567 mm of stack and 388 mm of reach, the geometry offers an endurance-style road riding position. It is the length of this bike that catches my eye. Admittedly, 420 mm-long chainstays are not in themselves out of the ordinary on an e-bike, but on those occasions that you forget you are looking at an e-bike, the longer rear end looks slightly dated.
The long chainstays and overall wheelbase, combined with a 60 mm trail and a 72.5° head angle, mean the Domestique feels very stable at speed, but certainly lacks the snappy acceleration and twitchy feeling I usually look for in a road bike. That is a personal preference, and the upside of this trade-off is a bike that feels remarkably stable even on rough surfaces.
In fact, so stable is this bike, I found myself happily free-falling down a steep, unevenly surfaced descent that usually has me hanging on for dear life. This stability and the slightly sluggish feel from the Domestique is perhaps partly due to the added weight even the lightweight Watt Assist motor adds.
Interestingly, HPS does plan to offer a custom geometry option at some point, so theoretically it should be possible to custom build a Domestique with your preferred geometry, but no details of this service have been announced yet.
The build
The Ekar groupset is a slightly peculiar choice for a road bike. The groupset has been designed specifically for gravel bikes, and hence its inclusion on a road bike was surprising to me.
I asked HPS founder and CEO Harry Gibings about the choice of groupsets. “When shifting your front chainring, you instinctively let off some torque to help with the shift, but an e-bike doesn’t understand this, and it keeps the power on,” he said. “So the 1x system with a wide range on the rear cassette eliminates this issue. The Ekar groupset offers that range through its 13-speed cluster.”
HPS has selected the 9-36 cassette option from the Ekar range matched to a 44T front chainring. Unsurprisingly given the partnership, Campagnolo wheels are also used with the new Shamal Carbon being the hoops of choice. Domestique customers will also have the option to upgrade to Campagnolo Bora wheels during the order process.
With the motor mounted within the frame, the Domestique is not restricted to a single rear wheel or hub. Changing the rear wheel is exactly the same process as chagning the wheel on a standard bike with disc brakes.
The Domestique rolls on 28 mm Pirelli P-Zero tubeless tyres. Although clearance is tight, HPS assures me the bike is happy to accept anything up to a 32 mm tyre. I didn’t have a set of 32s on site to test but I measured the frame at 36mm, so the 32 mm max tyre width makes sense.
A Deda Elemnti finishing kit completes the package with Superleggera RS handlebars and Superleggero RS seatpost and stem. However, I did have to swap the stem to achieve my desired handlebar reach.
Deda Resa 3 mm bar tape perfectly matches the colour scheme but was a bit thick for my liking. The thickness also greatly limited the tactile feedback from the Watt Assist Pro buttons.
The saddle is a Scicon Elan Power Ergo. The Elan is a short-nosed saddle, a design which is becoming increasingly popular on new bikes. However, saddles are a very personal thing, and unfortunately, this saddle did not agree with me.
Launch edition
The Domestique Watt Assist Pro will initially be available in a limited run of 21 models. Each bike will be specifically numbered based on its position within the 21 on offer. The bike I have here was effectively the first to roll off the production line, and as such it is named the 1-21.
The 1-21 is also unique in that it features Campagnolo text on the chainstay and logo on the head tube. The Campagnolo logo inclusion is a nod to the partnership between HPS and the Italian components manufacturer in the new bike’s design and testing phases. The remaining 20 bikes will still feature the Campagnolo Ekar groupset, but the HPS logo will adorn the head tube, and the Ekar logo will replace the Campagnolo text.
How does it ride?
HPS asked that I first ride the Domestique without the battery and motor – just like a standard bike. I found this a slightly strange request, given that I was to test an e-bike. But HPS founder Harry Gibbings convinced me of the benefit of riding without the battery to first understand the Domestique’s potential as a standard bike.
Although I was reluctant, logically this rationale made sense. I knew once I had a taste for the e-bike system, provided it worked well, the bike would never feel the same without it.
In hindsight, I am glad I rode the bike au natural first. It gave me a chance to appreciate the composure and stability mentioned earlier, and I could easily have forgotten on that first ride that this was an e-bike.
Having tested several high-end race bikes lately, the Domestique did not provide the same sensations. Yes, it was composed and tracked well on swooping corners at speed, but it lacked the acceleration and nimbleness of a lightweight modern race bike.
The model I tested weighed in at 9.5 kg including power meter pedals, Garmin mount, and my heavier stem, but without the battery. Although lightweight in comparison to e-bikes, this is remarkably heavy for a standard road bike.
That said, I found myself questioning time and again if the scales were accurate as the weight on the scales did not translate into a weighty feeling on the road. I have ridden winter bikes from this heavyweight division plenty of times, and never once found an ounce of joy in them. Those winter bikes were slow and felt slow. The Domestique neither felt nor moved slowly.
One thing I was less impressed with was the cable routing. In an era when cables are either entirely internal or even becoming obsolete in some cases, external routing is usually a rare treasure. However, the entry point for the rear derailleur cable and rear calliper hose at the head tube-down tube junction is at an angle that shoots the cables out directly into the path of my knees when pedalling out of the saddle.
I did manage to cure the knee rub by pushing the cables further into the frame, but this caused two other issues. Firstly, there was not enough length in the exposed cable to allow the handlebar to turn fully to the right. Secondly, that additional cable inside the frame started rattling profusely.
Some foam wrap over the cable outer could solve the rattle, but the routing may require some rethinking on the frame design. Either way, as seems to be the industry trend now, I envisage an integrated, and perhaps wireless solution will follow in subsequent HPS designs.
Admittedly, a racing cyclist in their early 30s with a 5.5+ W/kg FTP is not HPS’ target market for the Domestique, but this bike had me laughing out loud with enjoyment.
With the motor on, the Domestique was a joy to ride, especially on climbs. When the road tilted up, the Domestique came into its own. I felt a noticeable increase in my cadence, an evident speed increase, and climbs became enjoyable. Not easy, just more pleasant.
I have heard all the usual quips from e-bike naysayers: “that’s not exercise”, “you won’t get fit on an e-bike” etc. Strangely I found my first day with the motor one of my hardest sessions in a long time. I felt so good I was happier to push myself harder. A crest on the road which would typically sap my speed and energy became a blip which I could punch hard and carry speed over.
The only way I can describe the sensation is like mixing super form with a strong tailwind. It still hurts when you go hard, but the hurt is enjoyable and you want more.
There is the noticeable jolt you get through your legs when you try to freewheel with the motor in the higher assistance modes. This jolt is a shock at first and can be disconcerting when approaching corners on the first few rides. I did find I got used to it after several rides, and it is much less evident on lower assistance modes.
I did question what the motor might be doing when not in use. When pedalling backwards, there is remarkable resistance as the backward motion turns the motor. I assumed at least some of this drag must remain when pedalling unassisted.
Gibbens was keen to explain this was not the case. “The Watt Assist pro uses a clutch system; it only engages when you pedal backwards,” he said. “When the motor is on, it picks up the crown gear, which pushes it forwards. When pedalling forwards, there is effectively no drag.”
Due to the reduced torque of the Watt Assist Pro system compared to other systems, you do have to focus on maintaining a higher cadence to get the most from the motor. I found the ideal range to be somewhere around 85-95rpm. This wasn’t an issue for me personally, but those with naturally lower cadences might need to work on increasing that.
The Domestique gave me back the sensation of dancing up a climb I have only experienced on my very best days or in full Everesting mode. Sure there will be those who feel this is a fake good day, but the buzz was authentic.
I believe that good legs buzz is the real positive opportunity for e-bikes. No one has yet found the cure for ageing or the legal formula for year-round good legs, so bad days and weeks – even months – are inevitable. These bad-legs rides are not fun; they are often a chore and a necessity on the road to the next short-lived dose of good legs. With an e-bike, I believe we can have countless more good days.
HPS is now taking orders for the launch edition Domestique Watt Assist Pro, each costing €12,000 with delivery expected within three months.
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