Some years ago and even when the newton came on the market, the „real“ Powermeters cost in Europe much more than 1000€ (mostly more than 1500€) and 499$ were a fair price. Now there are new models available (Stages) and other companies have reduced their prices (Powertap) and now the prices start at 700€ + 100€ ANT+Bikecomputer = minimal 800€.
At Ebay I have seen an offer for the Newton at 499$ (=361€) but I suppose that I have to pay additional taxes. At the homepage of Ibikesports the price for Europe is 499€ (with or without german taxes?). Several european internet shop have prices between 660€ and 699€. My questions is: Are there owners who live in Germany who could say what they have paid? 499€, 699 ore even more? But 499€ or 699€: These price are too high when a DFPM cost 800€. I think Ibikesports should reduce their prices or consider to offer a new “Newton Sport” at a significant lower price……
Rolf
What about prices?
Re: What about prices?
Let's see...you report that you'll pay 800 Euros minimum for a "bottom-of-the-line" DFPM.
After spending your 800 Euros you'll either have to swap out your good bike wheel with a cheap, heavy wheel, or you'll get a crank PM that measures one leg only.
If you want a lighter wheel, or you own a better crank, you'll pay much more than 800 Euros.
And if you want a crank DFPM that measures both of your legs' output (which is something any serious cyclist should demand), you will pay much more than 1,000 Euros.
No matter which DFPM you purchase, to move your DFPM to your other bikes, you'll have to move the heavy wheel to your other bike, or move the left crank arm (assuming your other bike uses the same crank set), or move the pedals, or move the entire crank.
Alternatively, you pay 699 Euros for the iBike Newton+. The iBike Newton+ includes more memory, indoor trainer feature, CdA feature, and 2 year warranty upgrades, compared to the iBike Newton model.
With the iBike Newton+ you can use any wheel, crank, or pedals you want. You get superior accuracy compared to the one-leg PM, and equivalent accuracy compared to the hub, full-crank, or pedal DFPM (see the RennRad review posted here: http://www.ibikeforum.com/viewtopic.php?f=39&t=3019).
You don't have to buy a bike computer to read the iBike Newton+ power data data. You also get CdA measurements, wind speed, hill slope, and more. And moving the iBike Newton+ from bike to bike is EASY.
Maybe what we should do is raise prices, because very clearly the iBike Newton+ provides superior features and benefits.
After spending your 800 Euros you'll either have to swap out your good bike wheel with a cheap, heavy wheel, or you'll get a crank PM that measures one leg only.
If you want a lighter wheel, or you own a better crank, you'll pay much more than 800 Euros.
And if you want a crank DFPM that measures both of your legs' output (which is something any serious cyclist should demand), you will pay much more than 1,000 Euros.
No matter which DFPM you purchase, to move your DFPM to your other bikes, you'll have to move the heavy wheel to your other bike, or move the left crank arm (assuming your other bike uses the same crank set), or move the pedals, or move the entire crank.
Alternatively, you pay 699 Euros for the iBike Newton+. The iBike Newton+ includes more memory, indoor trainer feature, CdA feature, and 2 year warranty upgrades, compared to the iBike Newton model.
With the iBike Newton+ you can use any wheel, crank, or pedals you want. You get superior accuracy compared to the one-leg PM, and equivalent accuracy compared to the hub, full-crank, or pedal DFPM (see the RennRad review posted here: http://www.ibikeforum.com/viewtopic.php?f=39&t=3019).
You don't have to buy a bike computer to read the iBike Newton+ power data data. You also get CdA measurements, wind speed, hill slope, and more. And moving the iBike Newton+ from bike to bike is EASY.
Maybe what we should do is raise prices, because very clearly the iBike Newton+ provides superior features and benefits.
John Hamann
Re: What about prices?
Thanks for your answer John!
In fact the advantages of the Newton are low weight and the possibility to change it easily from on bike to another.
Weight:
The cheapest Powertap hub has a weight of 325g. This is less than low-cost hubs and about 80 – 110g more than high-end hubs. For me the difference is higher because I use a hub from Extralite (139g). So my bike would become 186g heavier but still leave below 6kg which is too light for races (minimum allowed weight 6,8kg). I think for most bikers who need really a powermeter the weight is no criterion because with the heaviest powermeter you can leave below the limit without any problems.
Possibity to change the powermeter from one bike to another:
I have only one bike …..
I expect that an newton is always significant cheaper than the cheapest DFPM because its accuracy is in principle lower than from a DFPM:
1. The calculation of power requires that you have always the same position on the bike as during calibration but at least sometimes you change your position and that can have a significant influence.
2. Special effects of aero-bikes with high profil rims and some directions of wind can produce a negative cdA-value of the bike (it is a little bit like sailing) and that cannot be included into the calculation of power because the Newton does not measure cross wind and does not know the exact form of frame and wheelset.
Last but not least:
The principle of the Newton is a good idea and its accuracy is probably high enough for most users and most situations. I´m interested in a Newton (Sport would be enough for me) but I expect a lower price than today and I wish a removable battery (for example 3 AAA-cells) because otherwise I must send it back every few years and that cost time and money.
Rolf
In fact the advantages of the Newton are low weight and the possibility to change it easily from on bike to another.
Weight:
The cheapest Powertap hub has a weight of 325g. This is less than low-cost hubs and about 80 – 110g more than high-end hubs. For me the difference is higher because I use a hub from Extralite (139g). So my bike would become 186g heavier but still leave below 6kg which is too light for races (minimum allowed weight 6,8kg). I think for most bikers who need really a powermeter the weight is no criterion because with the heaviest powermeter you can leave below the limit without any problems.
Possibity to change the powermeter from one bike to another:
I have only one bike …..
I expect that an newton is always significant cheaper than the cheapest DFPM because its accuracy is in principle lower than from a DFPM:
1. The calculation of power requires that you have always the same position on the bike as during calibration but at least sometimes you change your position and that can have a significant influence.
2. Special effects of aero-bikes with high profil rims and some directions of wind can produce a negative cdA-value of the bike (it is a little bit like sailing) and that cannot be included into the calculation of power because the Newton does not measure cross wind and does not know the exact form of frame and wheelset.
Last but not least:
The principle of the Newton is a good idea and its accuracy is probably high enough for most users and most situations. I´m interested in a Newton (Sport would be enough for me) but I expect a lower price than today and I wish a removable battery (for example 3 AAA-cells) because otherwise I must send it back every few years and that cost time and money.
Rolf
Re: What about prices?
The Newton is less expensive for two reasons: 1) its patented design is much less expensive to manufacture than ANY competitor design; 2) we believe that power is the most important measurement in cycling, and providing power measurement at affordable prices makes it possible for more cyclists to enjoy the benefits of power training.Rolf1 wrote: I expect that an newton is always significantly cheaper than the cheapest DFPM because its accuracy is in principle lower than from a DFPM:
1. The calculation of power requires that you have always the same position on the bike as during calibration but at least sometimes you change your position and that can have a significant influence.
2. Special effects of aero-bikes with high profil rims and some directions of wind can produce a negative cdA-value of the bike (it is a little bit like sailing) and that cannot be included into the calculation of power because the Newton does not measure cross wind and does not know the exact form of frame and wheelset.
Last but not least:
The principle of the Newton is a good idea and its accuracy is probably high enough for most users and most situations. I´m interested in a Newton (Sport would be enough for me) but I expect a lower price than today and I wish a removable battery (for example 3 AAA-cells) because otherwise I must send it back every few years and that cost time and money.
Rolf
While it's entertaining to debate the conditions where the iBike Newton "might" be less accurate in principle, that same kind of theoretical scrutiny, applied to ANY power meter measurement technology, reveals comparable (or greater) problems for them. Temperature compensation, false watts in crank power meters, electro-mechanical sensor drift over time, and ½ crank power meter assumptions are real issues.
The Newton has been shipping for over 2 years now, and we have yet to have the first one returned to us for battery replacement.
And the Newton's additional, unique measurement capabilities, including PowerStroke, CdA, wind speed, and more can't be found in any competitive product, at any price.
John Hamann
Re: What about prices?
Newton is expenssive too.
Re: What about prices?
times to times ibike newton goes on sale, have some patience and wait...
the ibike is very good for a power meter. You don´t need a 400$ garmin + 800$ stages power meter= +- 1200$ to see the watts on display
the ibike is very good for a power meter. You don´t need a 400$ garmin + 800$ stages power meter= +- 1200$ to see the watts on display
Re: What about prices?
Hello,
1200$? Why so much? In Germany a Newton+ is even a litte bit more expensive than a powertap G3 hub with a powertap Joule computer (712€ - 690€, see powermeter24.de) and I suppose in USA too.
That there is no misunderstanding:
The accuracy of the Newton is high enough for >90% of the users but a powertap hub is something else: It measures power and does not only calculate..... So a expect an significant lower price!!!!! Or would you pay the price of a Ferrari for only a Porsche????
Ciao Rolf
1200$? Why so much? In Germany a Newton+ is even a litte bit more expensive than a powertap G3 hub with a powertap Joule computer (712€ - 690€, see powermeter24.de) and I suppose in USA too.
That there is no misunderstanding:
The accuracy of the Newton is high enough for >90% of the users but a powertap hub is something else: It measures power and does not only calculate..... So a expect an significant lower price!!!!! Or would you pay the price of a Ferrari for only a Porsche????
Ciao Rolf
Re: What about prices?
OK, you got my blood pressure up a little bit...Rolf1 wrote:Hello,
1200$? Why so much? In Germany a Newton+ is even a litte bit more expensive than a powertap G3 hub with a powertap Joule computer (712€ - 690€, see powermeter24.de) and I suppose in USA too.
That there is no misunderstanding:
The accuracy of the Newton is high enough for >90% of the users but a powertap hub is something else: It measures power and does not only calculate..... So a expect an significant lower price!!!!! Or would you pay the price of a Ferrari for only a Porsche????
Ciao Rolf
1) Force measurement is the basis of power measurement. The PT hub measures applied forces. The Newton measures opposing forces. BOTH PRODUCTS MEASURE FORCES.
2) The Newton is just as accurate as the PT in power reporting, because the Newton MEASURES power. Check out the data for yourself:
http://www.ibikesports.com/wp-content/u ... -chart.png
The "calculation" myth is just wrong...
3) Don't forget that you have to add the price of the wheel to your PT hub.
4) Unless you use the same wheel on every bike, the cost of the PT solution shoots up enormously. We had a major European pro team switch from PT to Newton in 2014. Why? They couldn't afford the cost of having PT training and racing wheels...
John Hamann
Re: What about prices?
Hello
the Newton measures some influences (for example speed, wind speed etc) and calculate than power. The powertap hub measures the power directly. That can give the same results, but that is not sure!!! As I wrote already above there are some influences which connot be included into the calculation (changing position on the bike, cross wind...) so at least in some cases the power calculated by the Newton cannot be correct and must differ from the powertap values. Of course these may be only rare situations but they exist.
Sorry!
The Newton shows maybe 95% of the time correct values but in some situations the calculation the power values must be a little bit incorrect.
Pice of the rear wheel? I have only one rear wheel and with a powertap hub I pay only the price difference of the powertap hub and a normal rear hub.
Note:
There are several new powermeters announced with prices even below 600€, so the Newton gets more and more a problem. You should consider, whether you bring a new "Newton Sport" on the market for lower Price.....
Ciao Rolf
the Newton measures some influences (for example speed, wind speed etc) and calculate than power. The powertap hub measures the power directly. That can give the same results, but that is not sure!!! As I wrote already above there are some influences which connot be included into the calculation (changing position on the bike, cross wind...) so at least in some cases the power calculated by the Newton cannot be correct and must differ from the powertap values. Of course these may be only rare situations but they exist.
Sorry!
The Newton shows maybe 95% of the time correct values but in some situations the calculation the power values must be a little bit incorrect.
Pice of the rear wheel? I have only one rear wheel and with a powertap hub I pay only the price difference of the powertap hub and a normal rear hub.
Note:
There are several new powermeters announced with prices even below 600€, so the Newton gets more and more a problem. You should consider, whether you bring a new "Newton Sport" on the market for lower Price.....
Ciao Rolf
Re: What about prices?
You're concerned that the Newton uses calculations, assumptions and algorithms to indirectly estimate power.
Well, that same concern is equally true of the PT, SRM, Quarq, Power2Max, Pioneer, Garmin. et. al. all of which indirectly estimate power, based on calculations, assumptions and algorithms.
How can this be?
1) In physics power is defined as the product of force x speed. There is no sensor in the world that measures power directly; power readings are based on separate calculations of forces and speed.
The forces used in the power calculation can be either applied forces or opposing forces; THEY ARE IDENTICAL. The power meter's electronics multiplies the force and speed calculations together to calculate estimated power.
2) There is no sensor in the world that directly measures applied forces. There are sensors that directly measure strain (strain gauges) and then, using algorithms, estimate the applied force required to achieve the measured level of strain. For the applied force calculation to be accurate those strain/force algorithms need to account for temperature variation, non-linearities of materials, non-linearities of the strain gauges, manufacturing variations in the bonding of the strain gauges to the material, manufacturing variations in the dimensions and metals used in the hub/crank/pedals, "zero-offset" drift of the strain gauges, changes in the cyclist's applied force within the pedal stroke, and more. It is neither simple in principle nor easy in practice to do all this--this is a basic reason that good-quality direct force power sensors are expensive.
3) Applied force calculations are full of assumptions:
A. One-leg power meters (the ones that are relatively affordable) measure one leg only and assume that, in each pedal stroke, both legs apply identically the same force. In the real world, with real cyclists, we've seen power errors as high as 50% with one-leg PMs. What will be the accuracy of a one-leg PM be on your bike, with your riding style, each day you ride? Does your left/right leg strength vary during your ride? And does the person riding next to you have the same left/right strength distribution as you? The answers are unknowable.
B. Both-leg PMs require a complete crank rotation or complete wheel rotation before they can update the estimated power calculations. In real-life riding we've seen errors as high as 7% in "gold-standard" full-crank PM ride files, caused by errors related to the constant surging and pausing cadence rhythms of criteriums.
C. In rear wheel PMs there is a drive train loss from the crank (where the cyclist actually applies power) to the hub (where the strain gauge sensor is located). An assumption must be made about the magnitude of the drive train loss; not only is the value assumed, that value is assumed to be the same, no matter which kind of bike frame you have. Really? Why, then, do frame builders worry so much about the stiffness of their bike frames?
D. If you do big climbs, where temperature changes a lot, strain gauge readings can get into a lot of trouble. Also, since the crank/pedals/hub are places where 100% of the forces applied by your body are concentrated to propel the bike, even when not on hills you can get temperature changes due to frictional heating.
E. Also, applied force power meters are electromechanical devices that age mechanically as you put the miles on. The strain/force algorithms become increasingly inaccurate, in a manner unknowable to the cyclist.
4) Likewise, there is no sensor in the world that directly measures opposing forces. Air pressure is directly measured and then, using algorithms, estimates of opposing wind forces are made. Total opposing acceleration is directly measured and then, using algorithms (F = mA), estimates of opposing inertial forces are made. Friction (a fairly low component of total opposing force) depends on tires and road surface, and an algorithm is used to estimate frictional forces from bike speed.
Most certainly there are assumptions required to convert sensor readings into opposing force readings, but curiously enough, those assumptions are far less susceptible to systemic, unknowable errors that can plague applied force designs.
5) There is no sensor in the world that directly measures speed. There are sensors that measure the time difference between complete wheel revolutions, or crank revolutions, and then, using algorithms, estimate the bike speed or rotational speed of the crank. These algorithms need to have accurate inputs of wheel circumferences and precise timing of wheel or crank rotation. It is pretty simple to do this, so speed/cadence measurements are generally quite accurate.
No matter which kind of PM you choose, a lot of assumptions, algorithms and calculations are used to get a power number on your screen. And no matter what that power number is, it is an estimate derived from sensors that indirectly measure forces.
Well, that same concern is equally true of the PT, SRM, Quarq, Power2Max, Pioneer, Garmin. et. al. all of which indirectly estimate power, based on calculations, assumptions and algorithms.
How can this be?
1) In physics power is defined as the product of force x speed. There is no sensor in the world that measures power directly; power readings are based on separate calculations of forces and speed.
The forces used in the power calculation can be either applied forces or opposing forces; THEY ARE IDENTICAL. The power meter's electronics multiplies the force and speed calculations together to calculate estimated power.
2) There is no sensor in the world that directly measures applied forces. There are sensors that directly measure strain (strain gauges) and then, using algorithms, estimate the applied force required to achieve the measured level of strain. For the applied force calculation to be accurate those strain/force algorithms need to account for temperature variation, non-linearities of materials, non-linearities of the strain gauges, manufacturing variations in the bonding of the strain gauges to the material, manufacturing variations in the dimensions and metals used in the hub/crank/pedals, "zero-offset" drift of the strain gauges, changes in the cyclist's applied force within the pedal stroke, and more. It is neither simple in principle nor easy in practice to do all this--this is a basic reason that good-quality direct force power sensors are expensive.
3) Applied force calculations are full of assumptions:
A. One-leg power meters (the ones that are relatively affordable) measure one leg only and assume that, in each pedal stroke, both legs apply identically the same force. In the real world, with real cyclists, we've seen power errors as high as 50% with one-leg PMs. What will be the accuracy of a one-leg PM be on your bike, with your riding style, each day you ride? Does your left/right leg strength vary during your ride? And does the person riding next to you have the same left/right strength distribution as you? The answers are unknowable.
B. Both-leg PMs require a complete crank rotation or complete wheel rotation before they can update the estimated power calculations. In real-life riding we've seen errors as high as 7% in "gold-standard" full-crank PM ride files, caused by errors related to the constant surging and pausing cadence rhythms of criteriums.
C. In rear wheel PMs there is a drive train loss from the crank (where the cyclist actually applies power) to the hub (where the strain gauge sensor is located). An assumption must be made about the magnitude of the drive train loss; not only is the value assumed, that value is assumed to be the same, no matter which kind of bike frame you have. Really? Why, then, do frame builders worry so much about the stiffness of their bike frames?
D. If you do big climbs, where temperature changes a lot, strain gauge readings can get into a lot of trouble. Also, since the crank/pedals/hub are places where 100% of the forces applied by your body are concentrated to propel the bike, even when not on hills you can get temperature changes due to frictional heating.
E. Also, applied force power meters are electromechanical devices that age mechanically as you put the miles on. The strain/force algorithms become increasingly inaccurate, in a manner unknowable to the cyclist.
4) Likewise, there is no sensor in the world that directly measures opposing forces. Air pressure is directly measured and then, using algorithms, estimates of opposing wind forces are made. Total opposing acceleration is directly measured and then, using algorithms (F = mA), estimates of opposing inertial forces are made. Friction (a fairly low component of total opposing force) depends on tires and road surface, and an algorithm is used to estimate frictional forces from bike speed.
Most certainly there are assumptions required to convert sensor readings into opposing force readings, but curiously enough, those assumptions are far less susceptible to systemic, unknowable errors that can plague applied force designs.
5) There is no sensor in the world that directly measures speed. There are sensors that measure the time difference between complete wheel revolutions, or crank revolutions, and then, using algorithms, estimate the bike speed or rotational speed of the crank. These algorithms need to have accurate inputs of wheel circumferences and precise timing of wheel or crank rotation. It is pretty simple to do this, so speed/cadence measurements are generally quite accurate.
No matter which kind of PM you choose, a lot of assumptions, algorithms and calculations are used to get a power number on your screen. And no matter what that power number is, it is an estimate derived from sensors that indirectly measure forces.
John Hamann
Re: What about prices?
That was great explanation of how power meters come up the numbers for watts. So at the end of the day all those years of hearing about how the iBike only calculates or "estimates" power has really been a case of the pot calling the kettle black. Thank for the great write up John.
Re: What about prices?
Hello,Velocomp wrote:You're concerned that the Newton uses calculations, assumptions and algorithms to indirectly estimate power.
Well, that same concern is equally true of the PT, SRM, Quarq, Power2Max, Pioneer, Garmin. et. al. all of which indirectly estimate power, based on calculations, assumptions and algorithms.
How can this be?
1) In physics power is defined as the product of force x speed. There is no sensor in the world that measures power directly; power readings are based on separate calculations of forces and speed.
The forces used in the power calculation can be either applied forces or opposing forces; THEY ARE IDENTICAL. The power meter's electronics multiplies the force and speed calculations together to calculate estimated power.
2) There is no sensor in the world that directly measures applied forces. There are sensors that directly measure strain (strain gauges) and then, using algorithms, estimate the applied force required to achieve the measured level of strain. For the applied force calculation to be accurate those strain/force algorithms need to account for temperature variation, non-linearities of materials, non-linearities of the strain gauges, manufacturing variations in the bonding of the strain gauges to the material, manufacturing variations in the dimensions and metals used in the hub/crank/pedals, "zero-offset" drift of the strain gauges, changes in the cyclist's applied force within the pedal stroke, and more. It is neither simple in principle nor easy in practice to do all this--this is a basic reason that good-quality direct force power sensors are expensive.
3) Applied force calculations are full of assumptions:
A. One-leg power meters (the ones that are relatively affordable) measure one leg only and assume that, in each pedal stroke, both legs apply identically the same force. In the real world, with real cyclists, we've seen power errors as high as 50% with one-leg PMs. What will be the accuracy of a one-leg PM be on your bike, with your riding style, each day you ride? Does your left/right leg strength vary during your ride? And does the person riding next to you have the same left/right strength distribution as you? The answers are unknowable.
B. Both-leg PMs require a complete crank rotation or complete wheel rotation before they can update the estimated power calculations. In real-life riding we've seen errors as high as 7% in "gold-standard" full-crank PM ride files, caused by errors related to the constant surging and pausing cadence rhythms of criteriums.
C. In rear wheel PMs there is a drive train loss from the crank (where the cyclist actually applies power) to the hub (where the strain gauge sensor is located). An assumption must be made about the magnitude of the drive train loss; not only is the value assumed, that value is assumed to be the same, no matter which kind of bike frame you have. Really? Why, then, do frame builders worry so much about the stiffness of their bike frames?
D. If you do big climbs, where temperature changes a lot, strain gauge readings can get into a lot of trouble. Also, since the crank/pedals/hub are places where 100% of the forces applied by your body are concentrated to propel the bike, even when not on hills you can get temperature changes due to frictional heating.
E. Also, applied force power meters are electromechanical devices that age mechanically as you put the miles on. The strain/force algorithms become increasingly inaccurate, in a manner unknowable to the cyclist.
4) Likewise, there is no sensor in the world that directly measures opposing forces. Air pressure is directly measured and then, using algorithms, estimates of opposing wind forces are made. Total opposing acceleration is directly measured and then, using algorithms (F = mA), estimates of opposing inertial forces are made. Friction (a fairly low component of total opposing force) depends on tires and road surface, and an algorithm is used to estimate frictional forces from bike speed.
Most certainly there are assumptions required to convert sensor readings into opposing force readings, but curiously enough, those assumptions are far less susceptible to systemic, unknowable errors that can plague applied force designs.
5) There is no sensor in the world that directly measures speed. There are sensors that measure the time difference between complete wheel revolutions, or crank revolutions, and then, using algorithms, estimate the bike speed or rotational speed of the crank. These algorithms need to have accurate inputs of wheel circumferences and precise timing of wheel or crank rotation. It is pretty simple to do this, so speed/cadence measurements are generally quite accurate.
No matter which kind of PM you choose, a lot of assumptions, algorithms and calculations are used to get a power number on your screen. And no matter what that power number is, it is an estimate derived from sensors that indirectly measure forces.
thank you for your interesting answer John. For me as an engineer it is absolutely clear, that all powermeters measure something and calculate power on basis of the measured data. The big difference between "normal" powermeters and the Newton is, that the Newton assume that you have always the same position on the bike (cdA-value is constant), the rolling restistant is constant (only possible on roads with smooth surface, never offroad) and there are no (significant) effects of crosswind which can cause a negativ cdA-value of the wheels (effect like "sailing"). These effects are always included into the measured data of other powermeters. Maybe these are special effects for racing bikes (not for mountain bikes !!) because normally we have a similar Position on the bike for > 95% of the time and crosswind has only an significant influence when the wheels have high rims but in principle they exist.
Accuracy of measurements:
Of cause every measured data must have some deviations which depend on the principle of measurement, temperature drift etc. But please don´t tell me, that a Newton has no such problems!
For me it´s fact, that some influence cannot be included into the calculation of the Neweton which are included into the calculation of all other pwermeters and for me that´s a big difference.
Ciao Rolf
Re: What about prices?
We're making progress:
We agree that all these devices indirectly calculate power.
We agree that all these devices make assumptions.
We agree that the assumptions made in each device's particular design affects accuracy.
We agree that the devices' accuracy are, in real world conditions, affected differently, depending upon design choices and ride circumstances (temperature changes, CdA changes, fatiguing, pedaling style, sensor placement and quantity, etc)
It's great, too, that you're an engineer, because that means you know that error analyses can be performed to quantify the effect of parameter changes on accuracy.
Let's take your suggestion that the Newton is "right" 95% of the time, meaning that its CdA, Crr etc inputs are are correct 95% of the time.
What about the other 5%? You can run the calculations (we have) to quantify the effect of changes in CdA, Crr, have on watts in the 5% of time where they are "off". You'll find that real-world variations in these parameters have a negligible impact on overall accuracy. Furthermore: the actual watts difference caused by these changes depend on circumstances. For example, if a rider stands up while climbing a tough hill (this would be a real-world situation), his CdA may increase by 20%. But, in fact, he's climbing slowly, so opposing wind is low. And since the opposing force of wind varies as the cube of the wind speed, the impact of CdA changes on watts is negligible...
As a real-life example of this, I've taken a ride file from one of our Team Colombia guys. On a 40 minute long, 6% hill climb, he climbed at 12.2 mph, at a 356W pace. If he had stood up the entire climb (a ridiculous assumption), causing his CdA to increase by 20% for the entire hill climb, his DFPM watts would have been 359W. That's less than a 1% difference. And if he had stood up for only 4 minutes of the hill climb (a more realistic scenario) the difference would have been 0.1%.
The point I'm trying to make is simple: the assumptions used in the Newton generally have, in the real world, a demonstrably small impact on accuracy.
The assumptions the other guys make can cause, in the real world, a demonstrably large effect on accuracy.
Be aware...
We agree that all these devices indirectly calculate power.
We agree that all these devices make assumptions.
We agree that the assumptions made in each device's particular design affects accuracy.
We agree that the devices' accuracy are, in real world conditions, affected differently, depending upon design choices and ride circumstances (temperature changes, CdA changes, fatiguing, pedaling style, sensor placement and quantity, etc)
It's great, too, that you're an engineer, because that means you know that error analyses can be performed to quantify the effect of parameter changes on accuracy.
Let's take your suggestion that the Newton is "right" 95% of the time, meaning that its CdA, Crr etc inputs are are correct 95% of the time.
What about the other 5%? You can run the calculations (we have) to quantify the effect of changes in CdA, Crr, have on watts in the 5% of time where they are "off". You'll find that real-world variations in these parameters have a negligible impact on overall accuracy. Furthermore: the actual watts difference caused by these changes depend on circumstances. For example, if a rider stands up while climbing a tough hill (this would be a real-world situation), his CdA may increase by 20%. But, in fact, he's climbing slowly, so opposing wind is low. And since the opposing force of wind varies as the cube of the wind speed, the impact of CdA changes on watts is negligible...
As a real-life example of this, I've taken a ride file from one of our Team Colombia guys. On a 40 minute long, 6% hill climb, he climbed at 12.2 mph, at a 356W pace. If he had stood up the entire climb (a ridiculous assumption), causing his CdA to increase by 20% for the entire hill climb, his DFPM watts would have been 359W. That's less than a 1% difference. And if he had stood up for only 4 minutes of the hill climb (a more realistic scenario) the difference would have been 0.1%.
The point I'm trying to make is simple: the assumptions used in the Newton generally have, in the real world, a demonstrably small impact on accuracy.
The assumptions the other guys make can cause, in the real world, a demonstrably large effect on accuracy.
Be aware...
- Attachments
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- Hill climb
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John Hamann
Re: What about prices?
You've hit the nail on the head!ldmitruk wrote:That was great explanation of how power meters come up the numbers for watts. So at the end of the day all those years of hearing about how the iBike only calculates or "estimates" power has really been a case of the pot calling the kettle black. Thank for the great write up John.
John Hamann
Re: What about prices?
Coming back to the original question about price, as a recent EU purchaser I think that the Newton is competitively priced given the features as said before
What you have to remember is that this is a USproduct therefore you have to pay IMPORT DUTY + VAT and US prices are always quoted ex sales tax aka vat
Yes I could buy a power tap, but no good since I recently had custom wheels made. Yes I could buy a stages meter, my next choice, but I use an unusual crank length so no discount there and I have to change the crank and I only get reading from one side.
Bought a Newton, put it on the bike, got power data. Attached it to the PC and with power stroke saw some amazing data, I didn't wobble the bike as much as I thought I did and my pedal stroke is not that bad, try that with a stages meter.
The world is full of choices and low price doesn't always mean quality and best value
What you have to remember is that this is a USproduct therefore you have to pay IMPORT DUTY + VAT and US prices are always quoted ex sales tax aka vat
Yes I could buy a power tap, but no good since I recently had custom wheels made. Yes I could buy a stages meter, my next choice, but I use an unusual crank length so no discount there and I have to change the crank and I only get reading from one side.
Bought a Newton, put it on the bike, got power data. Attached it to the PC and with power stroke saw some amazing data, I didn't wobble the bike as much as I thought I did and my pedal stroke is not that bad, try that with a stages meter.
The world is full of choices and low price doesn't always mean quality and best value
Re: What about prices?
Thank you for your thoughtful comment. It's what keeps us moving forward!
John Hamann
Re: What about prices?
Rolf1 "I expect that an newton is always significant cheaper than the cheapest DFPM because its accuracy is in principle lower than from a DFPM:" is not true. I have had a Newton for years. When I first got one I compared it to a Garmin Vector 1 dual side, and after 9 months and 9,000 km, the two were virtually identical in readings.
In more recent times, this year, I compared the Newton 6 with Vector 2 dual side, and the Newton was somewhat MORE accurate.
When I compare reported power with calculated power, I have found no power meter to be of scientific lab accuracy, but Newton is accurate, and more importantly, repeatable.
I don't work for Velocomp, and John Harman can confirm I have been a pain in the butt for him over the years, but the Newton PM works as advertised.
It's small, light, simple to use, the Isaac software has no comparison.
Another point, I really like the info available on the Newton screens. I can pull up all manner of data during the ride beyond the usual averages. Things like TSS, kJ, calories, NP, etc. on just 2 screens accessible with large buttons (Garmin touch screen is really difficult). Garmin would need many little (unreadable) fields to get less information on-the-fly. Also, the Newton screen is better in daylight.
In more recent times, this year, I compared the Newton 6 with Vector 2 dual side, and the Newton was somewhat MORE accurate.
When I compare reported power with calculated power, I have found no power meter to be of scientific lab accuracy, but Newton is accurate, and more importantly, repeatable.
I don't work for Velocomp, and John Harman can confirm I have been a pain in the butt for him over the years, but the Newton PM works as advertised.
It's small, light, simple to use, the Isaac software has no comparison.
Another point, I really like the info available on the Newton screens. I can pull up all manner of data during the ride beyond the usual averages. Things like TSS, kJ, calories, NP, etc. on just 2 screens accessible with large buttons (Garmin touch screen is really difficult). Garmin would need many little (unreadable) fields to get less information on-the-fly. Also, the Newton screen is better in daylight.
Re: What about prices?
Wow, I really appreciate your post! And I don't remember any painful conversations...blp wrote: ↑Wed Jun 27, 2018 12:47 pm Rolf1 "I expect that an newton is always significant cheaper than the cheapest DFPM because its accuracy is in principle lower than from a DFPM:" is not true. I have had a Newton for years. When I first got one I compared it to a Garmin Vector 1 dual side, and after 9 months and 9,000 km, the two were virtually identical in readings.
In more recent times, this year, I compared the Newton 6 with Vector 2 dual side, and the Newton was somewhat MORE accurate.
When I compare reported power with calculated power, I have found no power meter to be of scientific lab accuracy, but Newton is accurate, and more importantly, repeatable.
I don't work for Velocomp, and John Hamann can confirm I have been a pain in the butt for him over the years, but the Newton PM works as advertised.
It's small, light, simple to use, the Isaac software has no comparison.
Another point, I really like the info available on the Newton screens. I can pull up all manner of data during the ride beyond the usual averages. Things like TSS, kJ, calories, NP, etc. on just 2 screens accessible with large buttons (Garmin touch screen is really difficult). Garmin would need many little (unreadable) fields to get less information on-the-fly. Also, the Newton screen is better in daylight.
It's nice to see SOMEONE with a similar point of view. I 100% agree that Garmin is a PITA to navigate. I agree that the Newton screen is much easier to see in daylight. And we worked very hard to make data easily accessible, with just a few button clicks.
As for accuracy...yes, yes, yes.
John Hamann
Re: What about prices?
Too bad Velocomp discontinued the Newton. If it was possible to add a GPS chip to it, no mapping just recording, the Newton would have been absolutely complete.
Re: What about prices?
I too like the Newton's readable screen over the hard-to-read garmin next to it.