iBike Newton PowerStroke  £779.00

8/10

Innovative power meter that offers results comparable to others along with features to improve your position and technique

Weight 136g   Contact  www.dhwagencies.com

by Mat Brett   July 2, 2014  

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.

The theory

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

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.

Downloaded information

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:

  • Distance
  • Energy
  • Calories burned
  • Climbing total
  • Braking
  • Normalised power
  • Intensity factor
  • Training stress score
  • Variability index
  • Coefficient of drag
  • Coefficient of rolling resistance
  • Temperature
  • Atmospheric pressure

Isaac also gives you minimum, average and maximum values for:

  • Power
  • Aerodynamic component of power
  • Rolling resistance power
  • Gravitational power
  • Speed
  • Windspeed
  • Elevation
  • Slope
  • Cadence
  • 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.

Accuracy

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.

Conclusion

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.

Verdict

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."

Rate the product for quality of construction:
 
7/10
Rate the product for performance:
 
7/10

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).

Rate the product for durability:
 
8/10

There are no moving parts to wear out. If you damage the speed/cadence sensor, any other ANT sensor will do the job.

Rate the product for weight, if applicable:
 
8/10

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.

Rate the product for value:
 
8/10

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).

Overall rating: 8/10

About the tester

Age: 43  Height: 190cm  Weight: 75kg

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,

 

28 user comments

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Interesting.

I do wonder how you quantify the different road surface friction levels though.

Boardman CX Team '14 | Cannondale CAAD8 '12 (written off, SMIDSY) | Scott Sportster '08

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posted by Gizmo_ [804 posts]
2nd July 2014 - 12:57

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I love that technology has advanced to the point algorithms and micro-sensors can do the same job as ironware - and in this case, far beyond (the accelerometer-based bike-wobbly-bit).

Now it just needs to be £500 cheaper.

Adding a £10 wind/baro pressure sensor as an Ant+ accessory and I can't see why a stem-mounted smartphone couldn't do all of this - existing smartphone accelerometers are good. The front-facing camera should be able to auto-detect being on the hoods, drops or tops based on silhouette.

Also, why can't the accelerometer detect rough vs. smooth road surfaces? I'm guessing you should put in your tyre size and pressure too.

I was told there would be Cake. Luckily there's http://TestValleyCC.org.uk

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posted by KiwiMike [463 posts]
2nd July 2014 - 13:28

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So it's just another guessometer, and more expensive than Stages - an *actual* power meter used by pro teams! I don't even want a power meter but, if I did, this isn't one.

posted by deblemund [81 posts]
2nd July 2014 - 14:12

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So this looks okay if you ride in the same position over consistent road surfaces (do such things exist?) using the same tyres (tyre suppleness having a large impact on rolling resistance) pumped to the same pressure. I'll stick with my Stages thanks.

posted by pwake [282 posts]
2nd July 2014 - 16:30

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deblemund wrote:
So it's just another guessometer, and more expensive than Stages - an *actual* power meter used by pro teams! I don't even want a power meter but, if I did, this isn't one.

Did you even *read* the article?

"the average power figures of the Newton PowerStroke and the PowerTap were within 0.5% of one another" yadda yadda within acceptable industry standard error levels yadda yadda basically the same yadda yadda

I'm sure the reviewer didn't stop every 100 yards to re-set the road surface type. He got within the margin of error across many different rides.

Just accept it folks, this shit works. It has a few 'drawbacks' (read: stuff you have to do differently but that is not 'hard'), but solves some other common issues with power meters - like having to swap your cranks, pedals, or have multiple compatible-wheelset bikes.

I was told there would be Cake. Luckily there's http://TestValleyCC.org.uk

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posted by KiwiMike [463 posts]
2nd July 2014 - 16:47

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KiwiMike wrote:
deblemund wrote:
So it's just another guessometer, and more expensive than Stages - an *actual* power meter used by pro teams! I don't even want a power meter but, if I did, this isn't one.

Did you even *read* the article?

"the average power figures of the Newton PowerStroke and the PowerTap were within 0.5% of one another" yadda yadda within acceptable industry standard error levels yadda yadda basically the same yadda yadda

I'm sure the reviewer didn't stop every 100 yards to re-set the road surface type. He got within the margin of error across many different rides.

Just accept it folks, this shit works. It has a few 'drawbacks' (read: stuff you have to do differently but that is not 'hard'), but solves some other common issues with power meters - like having to swap your cranks, pedals, or have multiple compatible-wheelset bikes.

Who rides in the same position though? I spend most of my time on the hoods, but climb on the tops and descend or go flat-out on the drops (don't most people?). I'd like it to work because I respect anyone who can code a decent algorithm taking in account this many variables.

Last night I would have considered trading a very loud baby for a really nice bike.

posted by notfastenough [3067 posts]
2nd July 2014 - 17:08

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notfastenough wrote:

Who rides in the same position though? I spend most of my time on the hoods, but climb on the tops and descend or go flat-out on the drops (don't most people?). I'd like it to work because I respect anyone who can code a decent algorithm taking in account this many variables.

Given the reviewer found within-margin-of-error levels of accuracy, I'm guessing it does work, somehow. Maybe if you are on a 'normal' ride where most time is on the hoods, a few minutes on the drops or tops evens each other out. Something like that. If you were going for a 10TT then setting it for 'aero bars' or whatever is a few seconds button pressing, I guess.

I was told there would be Cake. Luckily there's http://TestValleyCC.org.uk

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posted by KiwiMike [463 posts]
2nd July 2014 - 17:25

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im not a person interested in power numbers but am interested in the tech

just shows power is equatable via an algorythym

what this shows is all these cocks like srm/powertap are just desperately trying to say hardware is essential for power readings when in reality they are dipping their rods in a bowl of b.s.

crack on anyone that thinks they need power meter to go faster, but this device has just mullered mr srm with a soft punch

posted by russyparkin [579 posts]
2nd July 2014 - 17:43

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I love the tech and I agree with the article, its not about how accurate it is compared against another PM's its the consistency that matters.

But its just too expensive, its a souped up cycle computer !

posted by mikeprytherch [217 posts]
2nd July 2014 - 18:05

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deblemund: "actual power"? Do you even know what you mean by this? Why is a Stages giving "actual" power and why this Newton not?

posted by Paul J [582 posts]
2nd July 2014 - 18:16

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11% error if you ride in a different position is quite a big problem. Not having GPS is another issue. Unless they come up with a solution to both I can't see it catching on. Not to mention the price.

jaunty angle: bikes and communications
http://ragtag.wordpress.com

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posted by ragtag [154 posts]
2nd July 2014 - 18:45

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Innovative cycling accessory in "It's not 100% perfect for me so it's worthess / overpriced / inaccurate / unuseable" shocker!

I was told there would be Cake. Luckily there's http://TestValleyCC.org.uk

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posted by KiwiMike [463 posts]
2nd July 2014 - 18:52

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These guys look pretty pro: http://www.colombiacyclingpro.com/our-partners/
and you can get the more basic model from the states for a lot less than £799.

Also, there's no other power meter you can change between bikes in 30 seconds.

posted by weenyd [14 posts]
2nd July 2014 - 21:06

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KiwiMike wrote:
Innovative cycling accessory in "It's not 100% perfect for me so it's worthess / overpriced / inaccurate / unuseable" shocker!

I like the fact that they have approached the power measurement task from the 'other end', if you like. BUT it's not innovation when you end up with something that is less user friendly, no more accurate and less consistent than the existing technology. And unfortunately for them, their target market will be people who want a proven system (who wouldn't when you're shelling out big bucks) that doesn't depend on punching in a whole load of variables pre-ride, most of whom will already have an ANT+ compatible, GPS enabled head unit.

posted by pwake [282 posts]
2nd July 2014 - 21:50

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russyparkin wrote:
im not a person interested in power numbers but am interested in the tech

just shows power is equatable via an algorythym

Not quite sure what that means... but if you meant that you can guess the approximate power using the basic physics, a few sensors, a few more fingers in the air and the assumption that people don't markedly change their position on a bike - then, yes. Note even with a direct force measurement power meter you still need an 'algorythym' to turn strain-related voltage drops into a power reading, especially with non-round chain rings.

russyparkin wrote:
what this shows is all these cocks like srm/powertap are just desperately trying to say hardware is essential for power readings when in reality they are dipping their rods in a bowl of b.s.

No, no it doesn't.

russyparkin wrote:
crack on anyone that thinks they need power meter to go faster, but this device has just mullered mr srm with a soft punch

Hardly, even if it wasn't so bloody expensive.

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posted by fukawitribe [349 posts]
3rd July 2014 - 13:42

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The next iPhone is rumoured to have a barometric sensor in it. If that's true then there's little reason, with an Ant+ dongle and a well written app, that it wouldn't be able to do this.

It'll have a lot more processing power and the dedicated M7(8?) motion chip, and if done right could be a lot more intuitive.

posted by Gromski [39 posts]
3rd July 2014 - 14:45

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Why do I constantly read anti-power comments posted by people who I'm sure have never tried one? Could we have an anti-luddite rule where only experienced power users can post on a power gear page?
For the real world, the margins of error on this look fine, and as I seem to provide half of Palligap's annual profits from my power tap's constant need to be serviced / have new bearings / new torque tube, I'm desperate for something more reliable. Looks as if this could be it without all the mechanical bits to go wrong, (yes, I get that Stages can offer that too). Two questions really.
1. It can only be swapped from bike to bike easily if they each have the speed sensor, so how much are additional ones?
2. I assume it can input the results onto training peaks easily? Is the ANT software enough for that?

posted by Cresser [7 posts]
3rd July 2014 - 18:35

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Cresser wrote:
Why do I constantly read anti-power comments posted by people who I'm sure have never tried one?

Applies to pretty much anything on this site. Anti-Rapha from people who have never tried it, anti-anything from Gkam...

posted by andyp [850 posts]
3rd July 2014 - 18:43

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1). £30-£40 for the Ant+ speed/cadence sensor
2). Can export data easily to TrainingPeaks,Strava,etc
3). Record GPS using any other device and the s/w will then merge the files
4). Training with power makes me ride harder and more consistently on every ride. It'll make you faster than a new set of 404s, so why all the hate?

posted by weenyd [14 posts]
4th July 2014 - 7:46

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weenyd wrote:
4). Training with power makes me ride harder and more consistently on every ride. It'll make you faster than a new set of 404s, so why all the hate?

I'm not seeing much hate on this thread about using power - some questioning of the exact nature of the results from this particular meter (and the reasons for them), which seems reasonable.

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posted by fukawitribe [349 posts]
4th July 2014 - 10:01

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So, it's important to bear in mind all power-meters have to make assumptions. Further, none of them can measure power directly (that's pretty much impossible).

Power-meters measuring force on a pedal axle, crank arm, crankshaft or wheel axle, all use either electric-resistive or piezo-electric strain gauges to measure the *deformation* of the material. Note that that isn't even the force applied, never mind the power Wink. The applied load is extrapolated from the deformation. To make that they all come with built-in assumptions and approximations about the elasticity of the material the gauge is bonded to, and the quality of the bond. Those assumptions and approximations obviously have error in them, which can change over time.

E.g., other than steel under some limits, the elasticity of alloys slowly changes with repeated load cycles. The bonding of the gauge to the material can vary with manufacture (introducing non-linearities that might not be accounted for in calibration). The elasticity of the material changes with temperature - hence the need for temperature sensors and a table of assumptions in the meter, or in older systems a pre-ride zero-ing calibration (which isn't the most precise). The bonding of the gauge can age with time and load cycles, and change how the material deformation affects the sensor. Etc., etc.

This iBike Newton is as much a "real" power as the others, in that it measures forces - aerodynamic air pressure, atmospheric air pressure, the forces of acceleration - and then extrapolates from those measurements and some assumptions to give a power figure.

It's just silly to try claim this device is somehow not a "real" power-meter. This device makes a different set of assumptions to power-train force meters, and it seems to leave some dynamic variables unmeasured - as do power-train force meters. The question is how this affects accuracy and practicality.

I am quite surprised by just how accurate it appears to be. I'm not sure I'd trust its absolute figure given it can't measure your CdA, even if you did stay in the same position and same angle into the wind the whole ride. However, it seems like it could be useful for comparing rides at least, and even the absolute figures don't seem to be that inaccurate. That's really impressive.

That said, I wouldn't buy it. It's way too expensive. The device isn't worth that money at all. The cost I'm guessing is down to the R&D and software engineering they had to do - which seems impressive. To make this viable they need to amortise that R&D cost over a lot of units, which isn't going to happen at that price point.

It'd be really cool to see more cycle-computers measure aero-dynamic pressure. Wind resistance is the biggest variable when I try measure myself on a local climb. The iBike Newton shows you *can* get a pretty decent power figure out of that measure. I guess the ideal outcome is that some larger-volume cycle-computer manufacturer buys them to acquire the software R&D they've done on that.

posted by Paul J [582 posts]
4th July 2014 - 11:21

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Paul J wrote:
That said, I wouldn't buy it. It's way too expensive. The device isn't worth that money at all.

Thanks for the well worded summary Paul, and I agree with pretty much all of it especially this conclusion. Yes i'd probably use it if it were massively cheaper but that price, plus the issue with rider position significantly effecting the result, means I can't see it ever appearing on my power meter wish list. At least with a direct force power meter the power proxy is more consistent, modulo temperature compensation which is the real potential bug-bear - however that's pretty easy to adjust for so you bin the vast majority of the effect.

I do like the idea, and find the correlation against DFPMs compelling for basic out-dooor use (guess it's not going to work awfully well on a turbo/rollers) - but I think we need something like your ideal outcome to happen to get more traction in the market... or at least that's what i'd reckon, be really nice to be wrong on that.

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posted by fukawitribe [349 posts]
4th July 2014 - 12:05

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weenyd wrote:
These guys look pretty pro: http://www.colombiacyclingpro.com/our-partners/
and you can get the more basic model from the states for a lot less than £799.

Also, there's no other power meter you can change between bikes in 30 seconds.

Umm, people have been moving powertap's between bikes in less than 30 seconds for over a decade. And whats more its readouts are consistent even if, heaven forbid, you move from the hoods to the drops.

Garmin's vector can be moved in not much more than 30 seconds too.

Can't understand why road.cc have been so favourable to this meter. A power meter needs to do one thing only to be a useful training tool; be consistent. This device demonstrably fails to do this.

posted by giobox [265 posts]
6th July 2014 - 5:06

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giobox wrote:
[A power meter needs to do one thing only to be a useful training tool; be consistent. This device demonstrably fails to do this.

Ummm, the review shows the exact opposite of what you're saying it does. It shows that the iBike is consistent. If you mean that it gives different readings to those of the PowerTap when you alter your ride position from the one you've inputted, that's not a lack of consistency in the readings, it's a lack of consistency in your ride position.

You may or may not think that's a problem, but it doesn't mean it's inconsistent.

posted by Mr Turning [33 posts]
9th July 2014 - 10:41

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I've been using it since April and have found it to be very accurate. I was within 1% of a watt bike which is pretty good and what the website says. As for price, make friends with an American. They start at $500 here. With some of the upgrades, it can be around $600-$700. Feel free to do the rate change as you wish but you get the point.

The Isaac software, as a standalone product is OK but when used with things like Training Peaks (not a plug, just what I use) it makes the information much easier to use and review.

Battery like is OK but if you are uploading you rides, it will never be a worry.

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posted by The_Vermonter [3 posts]
10th July 2014 - 17:46

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Mr Turning wrote:
giobox wrote:
[A power meter needs to do one thing only to be a useful training tool; be consistent. This device demonstrably fails to do this.

Ummm, the review shows the exact opposite of what you're saying it does. It shows that the iBike is consistent. If you mean that it gives different readings to those of the PowerTap when you alter your ride position from the one you've inputted, that's not a lack of consistency in the readings, it's a lack of consistency in your ride position.

You may or may not think that's a problem, but it doesn't mean it's inconsistent.

Did you read the review?

"Over that ride, not surprisingly, there was a big discrepancy between the figures – nearly 11%"

11% discrepancy by changing position is not consistent. Other power measurement products don't vary their output because your hands get tired in the drops. I don't think many people will find a power meter that requires them to ride in the same position for the entire ride an appealing prospect!

posted by giobox [265 posts]
10th July 2014 - 17:59

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would be good if it was about £300 but for that kind of money you could by a stages crank or a powertap.

posted by markwill [20 posts]
14th July 2014 - 23:40

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All power meters make assumptions, and none of them are 100% accurate 100% of the time.

For those who favor one-leg power meters, check this out, just published in cyclingweekly.uk.co:

http://www.cyclingweekly.co.uk/fitness/training/power-symmetry-128109#P6...

"Studies show that the discrepancy between left and right legs can be very significant. For example, in one study, six highly trained competitive male cyclists rode a simulated 40km time trial on an SRM cycle ergometer, which measured the forces exerted by their left and right leg at the crank. The discrepancy between left and right leg varied through the time trial but averaged around 13 to 17 per cent."

What will you do with your one-leg power meter file at the end of your TT? When was it reading 13% high? When was it 17% low? For how much of the time? You have no way to know...

Suppose the Newton reads 11% different when you go into the drops. At least you KNOW when you are in the drops. Also, if you don't change ride positions frequently, the overall effect on accuracy is a fraction of 11%.

No such luck with a one-leg power meter. You have no way of knowing what its true accuracy is, within a ride, between rides, or between riders.

posted by kyzyl2 [1 posts]
17th July 2014 - 1:56

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