Terrain Dynamics AIRhub outdoor trainer review

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Terrain Dynamics is an Australian company built around an invention called the AIRhub, a programmable front wheel hub that is designed to add precisely measured doses of resistance. It’s purpose-built tool for outdoor training that promises cyclists a variety of benefits, and in this review, Australian tech editor Matt Wikstrom takes a look at them all.


In this era of smart indoor trainers, I expect most cyclists are familiar with the value that resistance training has to offer. One or two hard sessions each week often has a lot to offer, especially those that don’t have the time to spend long hours on the bike.

Of course, the whole notion of resistance training pre-dates smart trainers by several decades and many cyclists will have heard the old maxim, “train heavy, race light”. By forcing the body to adapt to a heavier load, a cyclist can improve their strength and endurance with regular sessions of resistance training.

One thing that has changed in recent years is our understanding of the loads required, due in part to the rise of heart-rate monitors and power meters. Where once cyclists had to feel their way through a weekly training regimen, now it has become scientific because they can measure and apply very specific loads to achieve a highly defined outcome.

Michael Freiberg is one rider that knows very well the value of a specific training program. He was part of Australia’s track cycling program, winning two medals at the 2010 Commonwealth Games — gold as a member of the team pursuit squad and silver in the 20km scratch race — and a world title in the omnium at the 2011 track cycling championships. The experience gave him enormous insight into the science of training, and it would shape his interests in the years that followed.

Indeed, 2012 was a turning point for Freiberg. He had high hopes of attending the Olympics, but he didn’t make the track squad. In the aftermath, the 21-year-old decided to take a step away from competition. He wasn’t finished with the sport, though, because he had an idea for an invention. And after testing the first prototype, he was convinced that it had the potential to overhaul the way road cyclists were training.

That invention was the AIRhub, and while it would take few years to bring the product to market, Freiberg was able to fulfil his vision for a brutally effective training tool. In the two years since its release, the AIRhub has been embraced by professional riders all over the world, and while Freiberg admits it’s a highly specialised tool, and very expensive (AUD$1,950/~US$1,530), he believes it can benefit any road cyclist that is looking to get the most from their training program.

A portable resistance unit for road bikes

The AIRhub is a wireless self-powered resistance unit designed to be used outdoors and on the road. The unit is controlled by a smartphone app that allows users to program how much resistance is applied during a training session.

In practice, what that means is that the AIRhub is designed to slow the bike down. While this effect is somewhat analogous to applying the front brakes, the AIRhub does it automatically and silently, just like a smart indoor trainer. In addition, there is a choice of five different modes for modulating the resistance of the AIRhub to different kinds of workouts.

The AIRhub will fit to any road bike with rim brakes.

At one end of the spectrum, there is a simple manual wattage mode that applies a constant load, ranging 0-100 extra watts, regardless of speed. At the other end, there is the W/km/h mode, which applies 0-2 extra watts for every km/h that the rider is travelling, so the load gently increases as the rider goes faster. The CdA mode functions in a similar way, mimicking an increase in the air resistance of the rider with an adjustment range 0-0.20.

The other two modes take advantage of the data coming from a heart-rate monitor (that is supplied with the AIRhub) and a power meter. In both instances, the rider selects a threshold for when the resistance kicks in (100-170bpm or 100-500W), so that every time their heart-rate or power output falls below it, the AIRhub will come on and force them to work harder.

In many ways, the AIRhub is analogous to an indoor smart trainer, however it doesn’t deliver workouts in the same manner. That’s because, in general, there is no need for the AIRhub to simulate different kinds of terrain; rather, it is designed to make any training session tougher, but compared to other strategies, the rider has very fine control over just how much tougher the session will be.

Breathing life into the AIRhub

When Michael started developing the AIRhub, he had a checklist of challenges. All were related to the difficulties he had experienced while training on the road, starting with finding a way to continue training effectively while enjoying the company of his team-mates.

The AIRhub requires a smartphone to control all of its features.

“When I was racing in Italy with the AIS [Australian Institute of Sport], that’s really where the idea for this system came to fruition,” said Michael. “It was in the lead up to the Olympics and I was doing everything right, which means going out by myself and watching the power meter numbers. My team mates were like, ‘What, you don’t want to go training with us? What’s wrong with us? Why don’t you want to come out?’

“It had nothing to do with that, though. If you want to be a good athlete, you have to do the training. You can’t be a social athlete and train the same way. So I imagined something where I could go riding with my friends and team mates where there were different abilities and skills. On the flats I could turn it up, and in the hills, where they’re better than me, I could turn it off. I could adjust it to whatever suited me the best for that day.”

Another aspect that was important was the way that the system behaved on the road. “I had been doing funny things for a number of years, like using heavier tyres, adding weights to my rims, filling my tubes with water, or going on a bunch ride with a mountain bike.

“If I used a heavy tyre, it would give me a certain kind of road feel. If I added weights to my rims, the road feel would be completely different. Putting water in my tubes was different again, but it wasn’t until I developed the first prototype for the AIRhub that I found the road feel and load I was looking for. It still felt a lot like a racing bike but I could give it a few percent extra. And the faster I went, the harder it got.”

A smartphone app provides users with a choice of five operating modes. Once a target is set in any of the modes, hitting the play button will activate the AIRhub. In this example, 30 watts of resistance has been set using the manual wattage mode.

Michael also understood that the system would have to be as easy to use. “Training is supposed to be hard. If you’re a professional athlete then it’s your job to go and train hard. We make that easier because you can train hard safer and you can train hard more specifically. Being an athlete, there’s no escaping hard, so the challenge is to do it with the least amount of effort, emotional and physical.”

Thus, the AIRhub was conceived as a wireless and self-powered device that could be installed on any road bike. And while it can generate some reasonably high loads, it was more important that it it do so in small increments.

“One of the general rules for training is that 10% extra resistance doubles the difficulty of the ride, so there’s no need for huge loads. There’s a lot of time in your ride where you could be going a couple of percent harder, but for whatever reason, you’re not. And that’s where you can pick up a few percent, here and there, by always keeping a load on the pedals.”

The pathway to developing the AIRhub

An e-bike motor served as the core of the first prototype for the AIRhub. It took some tinkering, but Michael was able to get the motor fitted to the fork of a road bike with a crude control unit mounted to the handlebars. It wasn’t pretty but it was enough to convince Freiberg that the idea had merit.

The AIRhub is essentially a dynamo that produces all of its own power to run the system. The back electromotive force that is generated by the system provides all of the resistance.

“We had the resistance, the right type of resistance,” said Michael, “but then we had to transform that into something that would fit on a racing bike to be used by professional athletes all around the world. That’s when we had to take it from a little hobby and something that I was just going to use for myself to the company that has become Terrain Dynamics.”

From the outset, it was clear to Michael that the final product would have to be self-powered with an electronic interface and wireless communication, so he understood that it would take a lot of time and money to get it right.

“The technical challenges for building something like this are enormous. We took a home-trainer and we shrunk it down to 1.5kg. It’s actually incredible how difficult it is to build something like this. But we had to go the whole way, we had to make the leap. It had be a robust product because if you put it out there, it’s not going to survive if it’s seen as a hobby or gimmick.”

The end result was a dynamo that uses back electromotive force to generate resistance. Users need to be travelling at 15km/h before the AIRhub starts applying resistance, and it will keep doing so until they exceed 45km/hr.

“The very first generation of the hub that we released almost two years ago had a humming sound. For training by yourself, it wasn’t a problem, but it was quite loud, quite intrusive, so if you went for a ride with your friends, it wasn’t ideal.

“It took us almost a year, or more, to be able to engineer a solution to be able to get around that issue. There were countless engineers that said it couldn’t be done with the components that were available on the market. The tapping that the AIRhub now generates is the byproduct of that process, the optimal byproduct. Not only does it reduce the sound, you only feel the tapping. It doesn’t affect your riding buddies and you know it’s on.”

Michael worked with several engineers, many from his home town of Perth in Western Australia, on the various aspects of the AIRhub. And as he moved into production in Taiwan, another trio of engineers was recruited to oversee production of the various components.

“I was lucky that one of my engineers from Perth, a production engineer, had worked with a lot of bike companies up in Taiwan, so I was able to go with him to Taiwan and have him help me get everything sorted out. It took a lot of time for our manufacturing partners to get it right because it was so different, but once we had that sorted, it was beautiful, and there is some top quality stuff coming out of the factory.”

What’s in the box?

The AIRhub is supplied as a complete front wheel, including a quick-release skewer and rim tape, that will suit any road bike with rim brakes. The 24-spoke wheel makes features a low-profile Alex rim (25.0mm tall, 23.6mm wide, 18.5mm rim bed), Pillar double-butted spokes, and alloy nipples for a total weight of 2.28kg without the skewer.

A 4iiii Viiiiva heart-rate monitor with dual Bluetooth- and ANT-connectivity is included with the wheel along with a universal mounting kit (Annex Quad Lock) for smartphones, wheel bag, and a user’s manual.

All of the functions of the AIRhub are controlled by an app via a Bluetooth connnection, so buyers will have to provide their own smartphone (or an iPad/iPod touch) before they can start using it. The app is free to download for iOS (9.3 or later) and Android (5.0 or later).

At face value, the Viiiiva heart-rate monitor may seem a little redundant, but it’s a problem-solver for anybody hoping to use an ANT+ power meter with the AIRhub. The Viiiiva is able to relay ANT+ data broadcast by power meters via Bluetooth to the AIRhub app; all that’s required is a bit of setup time using 4iiii’s free app.

The AIRhub comes complete with almost everything needed to start training with it. The only pre-requisite is a smartphone.

Price, warranty, and servicing

Terrain Dynamics sells the AIRhub direct to customers via its website for AUD$1,773/US$1,356/£1,019/€1,159, excluding shipping. That price includes the wheel along with all of the accessories described, plus a two-year warranty.

According the Freiberg, the only part of the hub that will ever require servicing is the axle bearings. The rest of the mechanism does not need to be serviced and there is no need for re-calibration at any point. At this stage, Terrain Dynamics takes care of bearing replacements however the company is considering appointing service centres around the world.

Putting the AIRhub to use

At 2.28kg, the AIRhub is easily the heaviest front wheel on the market, and at face value, many would be forgiven for asking why anybody would spend so much money to add so much weight to a road bike. I have to admit, I really enjoyed the irony, but as I put the AIRhub to use, I started to really appreciate what Terrain Dynamics has accomplished. Not only was it a highly polished product that worked flawlessly straight out of the box, it was a mercilessly effective training tool.

There’s always a moment before I start using any electronic device that relies on wireless interface where I dread the effort to get it running smoothly. In this instance, though, I didn’t have any trouble downloading and installing the AIRhub app on both an iPad 4 and iPhone5c and connecting with the wheel. A quick ride around the block, and the AIRhub was ready to start applying resistance.

The AIRhub app makes it easy to search for heart-rate monitors and power meters. Any ANT+ power meter can be used with the AIRhub thanks to the Viiiiva heart-rate monitor that is supplied with the wheel.

Likewise, the Viiiiva heart-rate monitor came to life without any fuss, and after setting up 4iiii’s app to recognise a set of Verve’s Infocranks, that data was also flowing to the AIRhub app. This heart-rate monitor, and its capacity to serve as a Bluetooth bridge for ANT+ data, is a thoughtful touch and proves that nothing has been overlooked in the design and execution of the AIRhub.

The AIRhub won’t start adding any resistance until the bike is travelling at least 15km/h, but early on, there were a few times when I started to worry that it wasn’t working because it didn’t come on when I hit the play button in the app. I even went so far as re-starting the app as I turned slow circles in a carpark until it dawned on me what the problem was. After that, I got into the habit of getting the bike going before I launched the app.

The tapping that comes from AIRhub was very subtle. It was something that could be both heard and felt, somewhat like the clickety-clack of a train on tracks. Otherwise, the wheel behaved largely like any other front wheel, though the extra weight was noticeable. Going back to a regular front wheel, the steering felt lighter, but the novelty of that sensation wore off after a few sessions with the AIRhub.

Given the variety of operating modes, I had a few options for assessing the performance of the AIRhub, and in the end, I settled on riding laps around a couple of short circuits (2-3km) that were largely flat, but not entirely, with and without the AIRhub running. In this way, I could get a feel for the effects of the AIRhub while using the various training modes and I could compare my times, heart-rate and power over a few laps.

Slecting an operating mode is simply a matter of touching the screen then using the slider to set the desired target. From left to right: power mode, heart-rate mode, CdA mode, and W/km/h mode.

The first thing that I noticed was how easy it was to trust the AIRhub when striving to maintain a given heart-rate or power output. The tapping of the device was always a sure sign that I needed to lift my effort, and once it stopped, I could ease off a little. By contrast, I had to watch my numbers a lot closer to achieve the same effect when I wasn’t using the AIRhub.

I’ve never had to train for long hours while trying to target a specific heart-rate or power output, but even over the course of a 20-minute session, I was able to enjoy the freedom that the AIRhub provided. I could lift my head and ignore my computer screen in favour of taking in my surroundings, yet I had enough feedback from the tapping to understand what kind of effort was required at any point in time. For those that spend a couple of hours watching their numbers during an endurance effort each week, the AIRhub should provide enormous mental relief.

The AIRhub consistently slowed me down for any given target heart-rate or power output. My average speed decreased 4-14%, depending on the course and the kind of effort I was trying to make. It also robbed me of any opportunity to pedal softly after topping small rises, so I was consistently working harder, and more often, just as Michael had promised.

This is where the AIRhub proved to be brutally effective because it removed the opportunity to recover as part of any self-pacing strategy. I also discovered I had to be very careful with the kind of target I was setting myself, especially when using the power mode, because small changes could make a big difference, again, as Michael had promised.

“The number one piece of advice that I give everybody who uses one, tries one, buys one is to be careful,” said Michael. “Because we all want to go max speed, max resistance on every ride but it only takes about two weeks before everybody realises that using the AIRhub like that is the equivalent of a mountain training camp.”

So, while the AIRhub can be used to very effectively test the limits of a rider, it is arguably more effective at ensuring the user maintains a minimum heart-rate or power output, at least for some training sessions. Once I started using the AIRhub in this way, then I found that I actually started to lift my output compared to what I could achieve with a self-paced effort. I could ride as hard as I wanted and still have room to ease off, yet the AIRhub was always there, ready to kick in, to make sure I never eased off too much.

Riding with the progressive resistance modes, CdA and W/km/h, provided a demanding challenge even when relatively small settings were used. For example, setting CdA to 0.5 required an extra ~15W to maintain the same average speed (29km/h) while using 0.5W/km/h demanded an extra ~20W. In both cases, the resistance gently increased as I gathered speed then eased off as I slowed on any rise in the road. The gentle modulation in resistance was barely noticeable yet I found myself responding to it by lifting my effort at higher speeds.

By contrast, setting a similar load (15-20W) using the manual wattage mode had me feeling a little defeated from the outset because there was no way to ease into the effort required. For those that live in flat areas hoping to replicate the same kind of effort required on a long climb, I expect this mode will do the trick.

The AIRhub performed flawlessly throughout the review period. I never had any problems pairing my smartphone with the device, the heart-rate monitor, or the power meter. And as far as I could tell, the AIRhub never hesitated in applying resistance when it was required. The hub itself remained trouble-free, too, as did the rest of the wheel.

More options for buyers

In the time since this review was originally published, AIRhub has added more options for buyers to choose from. That includes complete wheels with a 35mm carbon clincher rim or a HED Belgium Plus rim. A new simplified version of the hub has also been added to the collection, dubbed AIRhub Pro. This hub offers just two preset resistance modes — 1W/km/h and 2W/km/h — so there is no need for an app, a smartphone, or Bluetooth to operate the AIRhub Pro. Instead, there is just a simple switch that toggles between three settings: off, 1W/km/h, or 2W/km/h. The AIRhub Pro is available with the same choice of rims as the standard AIRhub, plus there is also an option to purchase the hub alone.

Summary and final thoughts

The AIRhub is an impressive product that does exactly what it promises to do with a minimum of fuss and effort. Given all of the technology involved in this product, it would be easy to forgive a minor idiosyncrasy or two, however there are none.

My training days are long behind me now, and the goals I have for my cycling are no longer performance-oriented, so I’m well outside the target market for this product. Nevertheless, it was easy to appreciate the potential of this product, especially for those riders that go searching for headwinds and long climbs for strengthening their endurance. The AIRhub will provide the same kind of resistance with far less fuss, more control, and greater reproducibility.

Some might count the ongoing need to use a paired smartphone to operate the AIRhub as a shortcoming. Others may find themselves wishing that it offered structured workouts like an indoor trainer, or that it could integrate with their preferred GPS device. According to Michael, Terrain Dynamics is working on all of these options. Importantly, none of them will require modifications to the hardware of the product, so I can only see the potential of the AIRhub expanding in the future.

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