iBike Power sensor

[BikeMax]

 

Bruce

 

Surely the other products also CALCULATES your power output' date=' they just use other inputs? Do you have any specifics available on how the polar unit calculates power?

[/quote']

 

SRM uses strain guages at crank to measure torque and PT uses strain guages at rear hub to do the same - then convert in to power.

 

No assumed values here.

 

Polar measures chain vibration to calculate chain tension and then uses speed to estimate torque and then convert to power - Bruce - you tell him...

 

[bruce]

 

No, the other units measures the variables directly:

 

Power = Force x Velocity

 

So in cycling

 

Power applied to the cranks is what your body produces.  The power is a function of the torque you apply to the crank and the rotational velocity (i.e. cadence)

 

SRM, measures these variable directly by replacing the spider on which your sprockets are mounted and uses strain gauges.

 

Ergomo, measures the torque applied to the BB shaft with strain gauges.

 

Powertap measures the torque the chain is applying to the rear hub, which is only slight less than the torque applied at the cranks, but is a better representation of the power reaching the road.

 

Polar: measure the chain speed and vibration.  Then based on the weight and type of the chain, calculates the tension in the chain and therefore the torque being applies to the rear cassette.

 

IBike: measures the forces against which you are working, and thereby the force you must be applying to overcome them - hence calculates power.

 

Now if you thank the iBike is interesting, there is a new unit that is actually mounted on the cleat of your cycling shoe - and measures the force applied by your foot to the pedal.  Marius, where's that joint your were talking about??

 

[bruce]

 

The iBike is calibrated by coasting from a fixed speed. It measures the incline so it does not matter what the gradient is.

So if you want to use it for TT's you calibrate it using a TT position' date=' for sea level you calibrate at sea level, for altitude you calibrate at altitude. It only becomes less accurate when you use it in circumstances other than what you calibrated for.

It is a sofisticated power calculating device based on measured parameters. The fears about it not being accurate are largely unfounded.

The only two real problems, for me, are that its measuring becomes compromised on corrugated roads, and that cannot work on an indoor trainer.

[/quote']

 

Well said.  The only other problem for me is that it's accurate operating range is less than the other devices - hence the need to calibrate it to it's operating environment.  This is a discipline that must be adopted when using any device, but even more so with the iBike.

 

[BikeMax]

 

It only becomes less accurate when you use it in circumstances other than what you calibrated for.

 

Unless you plan to ride in one position for the entire ride then you are either going to have to tolerate inconsistent readings or recalibrate in each position.

 

[101%]

would love to see some "REAL" accurate results and tests done on all these power thingys , all done under the same conditions. I think If one is intrested in power training and want to invest in a training tool like a powermeter then rather spend the extra cash, once you ad all the extras , pro's and cons to the Ibike then I feel rather go for something a little more expensive.

[domenic]

 Now if you think the iBike is interesting' date=' there is a new unit that is actually mounted on the cleat of your cycling shoe - and measures the force applied by your foot to the pedal. 
[/quote']

I have been wondering why nobody has done this. Where can one find out more?

[pedal on the downhills]

Well, i'll add my vote to the "opinion reserved" column. I see ibike has coyly revised their statement about accuracy from +/- 5 % (i.e. 10 % range, exactly the same as polar, i.e. uselss for high-end and accurate training) to "comparable with other powermeters... blah blah

 "Comparable" is not a unit of accuracy!

A steel bike bike is comparable to a titanium one after all..

 

Maybe the upgraded version is better? wait for some test results.

 

[bruce]

 

would love to see some "REAL" accurate results and tests done on all these power thingys ' date=' all done under the same conditions. I think If one is intrested in power training and want to invest in a training tool like a powermeter then rather spend the extra cash, once you ad all the extras , pro's and cons to the Ibike then I feel rather go for something a little more expensive.[/quote']

 

My absolutely personal opinion, is that a lot of people decide to look into power training, but are put off by the price of the top end units so they end up buying the cheaper ones.  Then when they have learnt enough about it they realise the limitations of the units they bought and end up buying an expensive one - pretty expensive exercise at the end of the day.

 

I have discussed doing such a test with Sean Badenhorst (Bicycling) I will be following it up with him.

 

[Maillot Jaune]

A good place to start learning about the iBike is the homesite! www.ibikesports.com From there you can find various discussion groups with lots of comparisons.

 

The rough road issue has been resolved in the firmware upgrade 1.08. The fact that new firmware can be downloaded is a real cool feature of this unit, as firmware upgrades become available continously improving the operation. The latest version, 1.10 made the keypad work much better as an example.

 

My exsperience with power in bunch riding has been very good as the windspeed measurement of the unit is very accurate. You only have to do a single "Coastdown" calibration with the unit in order to determine your aero profile. No need to repeat it again.

 

If the team from Cycling Peaks are positive about the unit, something must be working.....

[bruce]

 

A good place to start learning about the iBike is the homesite! www.ibikesports.com From there you can find various discussion groups with lots of comparisons.

 

The rough road issue has been resolved in the firmware upgrade 1.08. The fact that new firmware can be downloaded is a real cool feature of this unit' date=' as firmware upgrades become available continously improving the operation. The latest version, 1.10 made the keypad work much better as an example.

 

My exsperience with power in bunch riding has been very good as the windspeed measurement of the unit is very accurate. You only have to do a single "Coastdown" calibration with the unit in order to determine your aero profile. No need to repeat it again.

 

If the team from Cycling Peaks are positive about the unit, something must be working.....

[/quote']

 

Hmmnn... first post by the latest member joined.  You wouldn't happen to have a direct interest in this product would you?

 

If so, then why not just state the fact and put forward your perspective?

 

[Dr. Seuss]

My absolutely personal opinion' date=' is that a lot of people decide to look into power training, but are put off by the price of the top end units so they end up buying the cheaper ones.  Then when they have learnt enough about it they realise the limitations of the units they bought and end up buying an expensive one - pretty expensive exercise at the end of the day.

[/quote']

 

this is exactly what happened to me & my bicycle buying!  4 bikes in 12 months & finally I am happy.

 

not making the same mistake with the powermeter!

 

 

[GoLefty!!]

The underlying principle is sound i.e. the force that you produce is equal to the forces being applied to you in the opposite direction.  So to ride at 32 km/h you must apply the same force that the wind resistance is applying to you' date=' and the gravitational force if you are on a gradient.

I believe the problem lies is accurately measuring the forces that are being applied to you.  From an iBike perspective, many of these forces are predicited and not actually measured.  Same as the Polar - using chain speed and vibration, it predicts the tencion on the chain.

Some of the problems that I have heard regarding the iBike:
1. Does not behave well on rough roads where there is significant vibration.  Apparently the accelerometer goes into oscillation and spikes.
2. There are questions about it's performance in bunch riding.  Being mounted on the handle bars, it is assuming the wind speed it is reading is what is being applied to your entire body.  In bunch riding your chest shoulders and head will be encountering more wind resistance than your handlebars.

Not being able to use it indoors is a big problem for me (contrary to Owens theory).  Power based training requires sessions to be ridden at specific power levels and durations.  This is quite hard to do outdoors.  THen if you only use your power meter on certain rides, you are compromising it's value.
[/quote']

 

Que??

This is only true for objects at rest.

when the mass and air pressure forcing it down is counteracted by a reaction in the opposite direction.

 

If you're moving then the the forces acting on the body are the sum of the losses ie. air resistance and friction. These cannot be equal to your mass or you would not move.

On a Level road the mass is being supported

On an incline the mass either functions as a loss (incline) or as a gain (Decline)

 

 

Ibike works on some very sound principles.

It measures air speed (the opposing force)

It takes rider and bike mass into account so I assume you will set it up with your bike fitted with two full water bottles, and other bit sna blobs.

 

Since iBike measure, inclination, air pressure air resistance and temperature,  it can account for all losses against the Ideal where those losses don;t exist i.e a vacuum.

 

So it calculate Force = M.a

And P = F.v

and compares the v against the air speed which it taken from the Pitot tube in teh front of the unit. ( a calibrated wire is deflectedi.e.bent, by the air flowing over it and this is converted via algorithms into air speed.

 

Since the biggest loss is air resistance an assumed or normalised value for friction can be used and the Fmu= M.g. x mu.

 

pretty simple really and the trick lies in the calibration of the Pitot tube.

 

In a Bunch riding scenario, your head and shoulders are certainly the biggest contributor to drage but this is taken into account by cmparing the air speed against the measured velocity from the fork mounted sensor and magnet as in a normal computer.

 

If there is an error then it would surely be within the margin of error of other Power meters and therefore statistically insignificant when compared to those.

 

 

[bruce]

 

 

Que??

This is only true for objects at rest.

when the mass and air pressure forcing it down is counteracted by a reaction in the opposite direction.

 

 

In steady state' date=' i.e. moving at constant velocity, the sum of the forces acting on a body is zero

 

Force = mass x acceleration

 

If the forces are not zero, you will be accelerating not moving at a constant velocity.

 

 

 

If you're moving then the the forces acting on the body are the sum of the losses ie. air resistance and friction. These cannot be equal to your mass or you would not move.

On a Level road the mass is being supported

On an incline the mass either functions as a loss (incline) or as a gain (Decline)

 

 

Agreed, mass is only a factor when riding on an incline or decline i.e. when the force of gravity is working either for or against the rider.

 

 

Ibike works on some very sound principles.

 

As per the my very first sentence.

 

 

In a Bunch riding scenario' date=' your head and shoulders are certainly the biggest contributor to drage but this is taken into account by cmparing the air speed against the measured velocity from the fork mounted sensor and magnet as in a normal computer.

[/quote']

 

Unfortunately the unit is not measuring air speed at your head and shoulders, it is measuring it at the handle bars.

 

Question:  do you believe that the drag experienced by a rider riding in a bunch is the same if he rides upright, or if he rides in an aero position?  I believe that the drag is less if the rider is tucked in.

 

If there is an error then it would surely be within the margin of error of other Power meters and therefore statistically insignificant when compared to those.

 

I would hope so, otherwise people are paying a lot of money for something that cannot work.

 

However, that is not to say the unit does not have weaknesses.  I think it is important to discuss these weaknesses so that people that are about to shell out significant cash can make an informed choice.

 

[Windbreaker]

Windbreaker: What was wrong with the Polar stuff? I was asking Mother Xmas for a Polar Power sensor and cadence meter' date=' now looks like I wil have do a christmas list recall.   [/quote']

 

It was a bitch to setup. I'm a perfectionist with this sort of thing so I ended up making brackets to get the center lines perfect, but it was a bit UGLY.

 

But the Polar guys had me runnig around in circles regarding the variations I was seeing on my trainer. Finally I found something on the web which hinted at the problem but no official responses from Polar about. VERY frustrating.

 

I found that the road data was not too bad - I dunno say about 5% when I compared it with my PT but it was effectively useless on the trainer and I need a power meter that works indoors with the short winter days in the Cape.

 

 

[bruce]

 

Windbreaker: What was wrong with the Polar stuff? I was asking Mother Xmas for a Polar Power sensor and cadence meter' date=' now looks like I wil have do a christmas list recall.   [/quote']

 

It was a bitch to setup. I'm a perfectionist with this sort of thing so I ended up making brackets to get the center lines perfect, but it was a bit UGLY.

 

But the Polar guys had me runnig around in circles regarding the variations I was seeing on my trainer. Finally I found something on the web which hinted at the problem but no official responses from Polar about. VERY frustrating.

 

I found that the road data was not too bad - I dunno say about 5% when I compared it with my PT but it was effectively useless on the trainer and I need a power meter that works indoors with the long dark winter days in the Cape.

 

 

 

Biggest drawback I know of is the 5 second recording rate.  A lot can happen in 5 seconds.

[Windbreaker]

Bottom line - it has serious flaws. Too many variables to deal with. I'd be pleasantly surprised if the iBike turns out to be as accurate as the Polar even. 

The PowerMeters that Hunter Allen was comparing it to' date=' and found it "damn close to my other power meters." was actually SRM & PowerTap... not to bad for a flawed little thingy with too many variables to deal with... [/quote']

Like I said ... ask him for the comparative data then "damn close" will have some meaning.

 

Compared to you I live "damn close" to Hermanus but that's still a long way for you - right?

 

Lets see data. At this stage I remain sceptical, but I am quite happy to be wrong about this one. More "power" to the people!