The iBike Newton PowerStroke is an innovative power meter that provides results comparable to other well-respected power meters on the market, and it offers features to help improve your cycling technique and riding position too.
Most power meters measure direct force using strain gauges – in the rear hub in the case of the CycleOps PowerTap, in the pedal axles in the case of the Garmin Vector, and so on. The iBike system is different in that it tackles the problem from the opposite angle. It measures the forces that you have to overcome.
Newton's third law of motion says that for every action, there is an equal and opposite reaction. So, if you measure the forces opposing your forward movement, you can work out the power you must be putting out to overcome them and travel at a given speed. That's lateral thinking.
As a concept, that doesn't sit well with many people. Okay, you can't argue with the theory, but surely it's going to be much more accurate to calculate how much power you're putting into your pedals by measuring the force going into the pedals, for example, rather than by working out the forces opposing your forward motion caused by hills, wind resistance, friction and acceleration. That has to be a round-about way of doing it, doesn't it, with much more potential for errors to creep in?
The iBike system relies on you inputting the weight of yourself, your bike and your equipment, tapping in your height, telling it what bike position you ride in and the type of surface you're riding over. How can it possibly come up with any meaningful measurement?
That's what you're thinking, right? And who could blame you? Scepticism is healthy, otherwise we'd all be travelling around in Sinclair C5s. But our results suggest you should rein in those reservations.
How the Newton PowerStroke calculates power
First, let's take a look at how the Newton PowerStroke does its thing.
The system comprises a wireless speed/cadence sensor (20g) that you mount on your chainstay and a head unit (72g) that fits on a mount (44g) on your stem or handlebar. Bearing in mind that you'll probably be riding with a bike computer anyway, the additional weight is minimal.
Accelerometers inside the Newton measure acceleration, a sensor measures elevation, and another sensor measures wind (there's a little hole in the front to let air in). iBike reckon that the sensors experience very little stress so there's no need to recalibrate them over time.
When you set up the Newton you enter the total weight of you, your bike and equipment; your tyre size circumference; your height and usual ride position; and the road surface. The Newton uses these figures to come up with your coefficient of drag (CdA) and coefficient of rolling resistance (Crr).
You might change your ride position over the course of your ride (more on that later), or your weight might vary as you sweat or if you stop and use the toilet, for example (drinking from a bike-mounted water bottle won't change the combined weight of you and your bike, of course), but iBike reckon that in most cases changes like these won't much affect the overall accuracy.
The Newton takes the air pressure, accelerometer and speed measurements to calculate the total force working against you. The total opposing force multiplied by your speed gives your power.
Set up is relatively easy. iBike have a whole bunch of comprehensive videos online.
Once you have attached the mount to your handlebar or stem – that's a simple Allen bolt job – it's easy to slide the USB rechargeable head unit on and off.
Getting the speed/cadence sensor to pick up magnets you attach to the crankarm and a spoke seems a bit old school in these GPS times, but it's tried and tested technology. Communication between the speed/cadence sensor and the head unit is via the widely used ANT+ protocol.
Once fitted, you have to perform a 10 minute 'calibration ride' which simply involves riding along an open road for five minutes, turning around and riding back. This calibrates the Newton's wind and tilt sensors.
If you have another bike set up with an ANT+ speed/cadence sensor and a mounting bracket, shifting the Newton+ across takes just a few seconds, including switching to the second bike's profile in the head unit (you can set four different profiles).
Riding with the Newton PowerStroke
The Newton PowerStroke offers you two main screens. The first one shows you speed, distance travelled and elapsed time, while the second one shows you speed, power in watts and cadence.
Unless you're a metronome, your power measurement will change constantly so you can adjust the Newton to give a rolling average (a 10-second or 30-second average, for example) to provide some stability.
Press a button and you can access your average and maximum statistics (speed, power and cadence) while another button gives you environmental information (temperature, time of day, slope, wind speed and elevation). You can also have your heart rate displayed if you add an ANT+ heart rate strap.
If you're coming from something like a Garmin Edge computer that has loads of pages and loads of data fields, that's going to seem pretty basic.
Plus, with something like a Garmin, you can customise the pages to give exactly the type of info you want to see and where you want to see it. With the Newton+ you can hide any parameters that don't interest you and decide whether you want each measurement large or small, but that's it. Another major difference is that there is no GPS derived information (unless you use a smartphone and Newton's Tracker app, in which case you can export to Strava).
All in all, you'd have to describe the display options as limited and I didn't find the navigation especially intuitive. Plus, changing settings via the head unit involves a lot of scrolling and deciphering of messages. '4 SET PrOF', for example, means nothing in plain English, so you need to go through the online Operating Instructions (there are 50 pages) to find out what it means (if you're interested, it actually means that all setup data you have entered and any calibrations you have performed are stored in 'Profile 4').
If you fork out for something with the capabilities of an iBike Newton PowerStroke, you have to accept that you're going to have to spend some time learning how to use it properly. I just think that the user interface could be more clearly signposted.
One interesting feature is that you can see a snapshot of your coefficient of drag (CdA) while you're out on the road. The lower the CdA, the more aerodynamically efficient you are, so you can instantly see the effects of altering your position, clothing and equipment.
The Newton PowerStroke has more features too, such as a built-in cycling fitness assessment so you can test physiological changes over time, for example, and it can provide interval training workouts for your level of fitness and your goal.
You can use the Newton PowerStroke on an indoor trainer. Obviously, you don't get any info from the head unit sensors, just from the speed/cadence sensor. Instead, you choose the trainer you have from a list of options (about 200 trainers and rollers are included), along with the level you're using on that trainer (there are power curves for each), and the Newton PowerStroke uses that, along with the speed and cadence measurements taken from the rear wheel and crank, to produce a power measurement.
After your ride, you download your ride information to Newton's Isaac software on your computer (PC or Mac) via a USB cable. Isaac doesn't look as polished as many online data storage sites but it gives you a lot of data from your ride:
- Calories burned
- Climbing total
- Normalised power
- Intensity factor
- Training stress score
- Variability index
- Coefficient of drag
- Coefficient of rolling resistance
- Atmospheric pressure
Isaac also gives you minimum, average and maximum values for:
- Aerodynamic component of power
- Rolling resistance power
- Gravitational power
- Heart rate (as long as you've used an ANT+ strap which isn't included)
You can get all of these statistics for any section of the ride you choose.
Isaac gives you graphs of your power, speed, cadence, heart rate, elevation, slope and wasted watts (more on that coming up). You can smooth the data to plot averages of each parameter anywhere from five seconds to an hour. You can view graphs covering your whole ride at once, or in smaller segments.
Interestingly, Isaac shows on the graphs when you had a tailwind and when you had a headwind (it does this be comparing your speed with its power calculations), when you were drafting (from a reduction in wind resistance), when you were coasting, when you were braking, and when you were riding out of the saddle (from the extra motion associated with standing).
You're dubious? I did one ride where I noted all the sections where I got out of the saddle and Isaac got it right every time.
One of the most interesting features is the Powerstroke pedalling analysis function (a Newton without Powerstroke is £599).
Newton PowerStroke records your ride data 16 times per second (it knows when your crank passes the cadence sensor, then divides the rest of the time into 16), and Isaac gives you a side-on crank view showing the acceleration of the bike as you go through the pedal stroke. It overlays this with an 'ideal' pedal stroke. The idea, of course, is that you can use this as the basis for improving your technique, and quantify your improvements over time.
Powerstroke also processes the data to analyse your wasted motion – crank motion that leads to the bike wobbling front-to-back and side-to-side – and quantifies this. It might tell you that you've wasted 7W of power, 52% due to side-to-side motion, and 48% due to front-to-back motion, for example. It'll also give you the amount of distance you could have gained and the amount of time you could have saved with purely forward motion.
You can share your ride files with a coach, for example, and upload them to something like Training Peaks.
So, how accurate is the Newton PowerStroke? That's the question that's most interesting.
Well, let's preface this by saying that the absolute wattage figures of a powermeter probably aren't all that important to you. Whether you call a certain output level 240W or 250W usually doesn't make much difference (unless you're comparing figures across different devices, which I really wouldn't advise because all systems measure differently and all have a margin for error), it's the consistency that really counts. You want what you're calling 250W today to be the same as what you're calling 250W next week and next year, so you can use it for objective analysis.
All we can really do to test accuracy is to use the Newton PowerStroke alongside other systems and see how the results compare. All the powermeter brands we've spoken to respect the data from a CycleOps PowerTap system, so we set up the Newton PowerStroke and a PowerTap on the same bike and used them on the same rides.
iBike say that the Newton PowerStroke is accurate to +/-2%, which is the same as most other powermeter manufacturers claim for their products (CycleOps claim 1.5% for the PowerTap).
So, what did we find? Well, despite our initial scepticism, the results from the Newton PowerStroke followed those of the PowerTap very closely indeed.
On most rides I've done, the average power results of the Newton PowerStroke and the PowerTap have been within 2.5% of one another. That's well within the bands of accuracy claimed by the two manufacturers.
Here's a 46-minute section of a ride from yesterday morning, for example, where the average wattages between the two systems are within 1.2%. I've smoothed the power figure to give 30-second averages just to make it easier to see. The white line represents the data from the Newton PowerStroke, the green line shows data from the PowerTap.
As a rule, the Newton PowerStroke gives the peak figures a little higher than the PowerTap, but they track one another really closely.
On another ride I did yesterday I tried to confuse things by riding with my intensity all over the place, like a fartlek session. I've only smoothed the graph to give 10-second averages this time but the two lines still follow one another remarkably well. Over the whole of that 54-minute ride, incidentally, the average power figures of the Newton PowerStroke and the PowerTap were within 0.5% of one another.
What if you alter your ride position? Well, I did another ride yesterday with my hands on the handlebar drops despite having the Newton PowerStroke set up for riding on the hoods. Over that ride, not surprisingly, there was a big discrepancy between the figures – nearly 11%. In other words, you have to do what you say you're going to do in order to get accurate results.
These are just example rides, by the way. We've been using the Newton PowerStroke for nearly three months and these are representative of the results we've been getting.
There are a whole bunch of other features if you use a Newton PowerStroke alongside a direct force power meter, but we don't imagine too many people are going to have access to two, so we won't go into depth here.
Overall, if you put your figures in carefully and keep them updated, the Newton PowerStroke does give results that correspond very closely with those of a PowerTap – within the levels of accuracy claimed by the manufacturers of each device, in our experience.
Good things about the iBike Newton PowerStroke
- Low weight.
- There's no maintenance, nothing to wear out and no need for recalibration.
- Setup is relatively easy and requires no special tools.
- Swapping between bikes is easy if you have another mount and speed/cadence sensor.
- The power values given are very similar to those of a PowerTap.
- Interesting software features, especially if you pay the extra for PowerStroke.
- Relatively low price for a powermeter.
Not-so-good things about the iBike Newton PowerStroke
- The on-bike display is basic.
- Not the most intuitive user interface.
- You need to fix a speed/cadence sensor to your bike.
- There's no GPS function (unless you use it alongside a smartphone app).
- You need to update inputs to get consistent figures.
- Swapping position during a ride will affect results.
Innovative power meter that offers results comparable to others along with features to improve your position and technique
road.cc test report
Make and model: iBike Newton PowerStroke
Size tested: Black
Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
iBike say, "The iBike Newton PowerStroke is the world's only power meter that measures power AND helps you pedal more economically.
"Only the iBike Newton PowerStroke has a microcomputer that delivers power measurement, power training programs and power testing in one super-light unit, with the easiest-to-read display around.
We're often asked, how does iBike Newton PowerStroke work? Where are the strain gauges? Simply, the iBike Newton uses advanced accelerometers and pressure sensors from the space program to measure your power and pedaling motion.
The iBike Newton PowerStroke is a power meter and more. It is a world class cycling computer. It is incredible software. It is a personal trainer that tests your limits and then improves them.
All in one unit. All for one purpose. To help you get more results and more fun in your cycling."
Tell us some more about the technical aspects of the product?
Here's iBike's explanation as to how the Newton PowerStroke calculates power:
"Accurate, Proven, Solid-State Sensors
Digital accelerometer and dynamic pressure sensors, the kind used in aerospace applications, are mounted inside the Newton. These sensors measure forward acceleration and opposing air pressure. Because the sensors experience very little stress they require no maintenance or periodic recalibration.
A wireless sensor mounted on the chain stay measures bike speed.
Aerodynamic and Frictional Drag Coefficients
As part of initial setup the user enters total bike/rider weight, tire size and road surface, rider height, and ride position. From these inputs the rider's CdA (coefficient of drag), and bike Crr (coefficient of rolling resistance) are determined.
iBike 'Physics Engine' Converts Sensor data into Power
On the road, the iBike Newton's 'Physics Engine' converts air pressure, accelerometer and speed measurements into opposing wind, hill slope, acceleration, frictional forces.
The total opposing force, multiplied by bike speed, equals cyclist power.
Because it accurately measures opposing forces and speed, the iBike Newton accurately measures power."
Get your inputs right and update them regularly and the iBike offers results comparable to those of direct force power meters with a bunch of extra features besides. My reservation is that I'd prefer GPS (without the need to carry a smartphone).
There are no moving parts to wear out. If you damage the speed/cadence sensor, any other ANT sensor will do the job.
Assuming you'd be using a bike computer anyway, you're only adding the weight of the speed/cadence sensor and the magnets that trigger it to your bike, along with a mount that's slightly heavier than normal.
Bearing in mind that you don't need to buy a bike computer (unless you want GPS), this is a cheap option by powermeter standards.
Tell us how the product performed overall when used for its designed purpose
I was sceptical – massively sceptical – but the bottom line is that the results we got were very similar to those from direct force power meters.
Tell us what you particularly liked about the product
I've listed positives and negatives at the end of the review.
Did you enjoy using the product? It worked well, yes.
Would you consider buying the product? Possibly, but I really want GPS (without the need to use a smartphone).
Would you recommend the product to a friend? Perhaps, depending on features they were after.
Anything further to say about the product in conclusion?
The tech here is incredibly smart. I'll be honest: I didn't think the Newton PowerStroke would give results that were in any way comparable to those of a direct force power meter, but I was wrong. It's very good value, especially if you're in need of a new bike computer (because the head unit is the main part of the system).
About the tester
I usually ride: My best bike is:
I've been riding for: Over 20 years I ride: Most days I would class myself as: Expert
I regularly do the following types of riding: commuting, club rides, sportives, general fitness riding,