I live Damn close to Kendra............
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iBike Power sensor
Started by Windbreaker, Dec 13 2006 05:34
61 replies to this topic
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#50
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Ultimate Hubber
Posted 13 December 2006 - 02:51
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I live Damn close to Kendra............
Kendra ......
By the way what happened to the Britney thread by the way, looked around this morning but could not find it, no that i wanted to post any thing more but noy sure where it went to.....
Bermuda Triangle.....
tooHot!!!! is under your bed!
#51
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Ultimate Hubber
Posted 14 December 2006 - 05:57
[QUOTE=bruce] [QUOTE=GoLefty!!]
[QUOTE=GoLefty!!]
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.
[quote]
[QUOTE=GoLefty!!]
[quote]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.
[/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.
In steady state, 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.
In steady state, 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.
[/QUOTE]
When is anything ever moving at a constant velocity? This is an ideal scenario that only works in a Matric exam paper. In the real world friction and air resistance are always slowing you down therefore you need to apply power to overcome them. If you stop pedalling the losses will eventually stop you.
[QUOTE=GoLefty!!]
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.
[/QUOTE]
In the real world here is always a gradient, a perfectly flat road does not exist therefore the inertial forces are always in play.
As per the my very first sentence.
As per the my very first sentence.
[quote]
In a Bunch riding scenario, your head and shoulders are certainly the biggest contributor to drag but this is taken into account by comparing the air speed against the measured velocity from the fork mounted sensor and magnet as in a normal computer.
[/QUOTE]
[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.
[/QUOTE]
[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.
[/quote]
It would ned to be measured but I do beleive that difference is insignificant when compared to the drag generated during calibration. Everything is relative to that point.
How much time will a rider spend on the tops of the bar when riding in a bunch?
How much time will they sond on the brake hoods where they can control speed more effectively and have more control?
I go with the latter, which is the recommended calibration position.
Over a 6hr ride is the time spent on tops of the bars significant to scew the power data? I doubt it.
[QUOTE=GoLefty!!]
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.
[/QUOTE][quote]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.
[/QUOTE]
Sure weaknesses should be discussed for any item,but this should not be the focus of a discussion.
A purchase decision ismade for many reasons, but mosty cost / performance ratio drives this type of decision.
Also, the This-guy-on-a-forum-who-is-Mr X- in-his-field-and-therefore-must-be-right-and-has-no-vested-interest-in-my-decision says Item B is the best and therefore I want it is a common reason why often good products don't sell well.
Every Power meter will have drawbacks, whats important is that any user only uses one type of power meter to avoid variances in the design of each.
It's the change over time that is important,not the brand of power meter.
#52
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Ultimate Hubber
Posted 14 December 2006 - 06:13
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Every Power meter will have drawbacks, whats important is that any user only uses one type of power meter to avoid variances in the design of each.
It's the change over time that is important,not the brand of power meter.
What is important in measuring power is consistency of output - this is where the Ibike is most flawed - IMO there are just too many chances of inconsistent data for it to represent good value - especially when the price is comparable to a PT Std.
#53
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Ultimate Hubber
Posted 14 December 2006 - 06:23
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When is anything ever moving at a constant velocity? This is an ideal scenario that only works in a Matric exam paper. In the real world friction and air resistance are always slowing you down therefore you need to apply power to overcome them. If you stop pedalling the losses will eventually stop you.
Okay, since you do not believe my understanding of elementary physics, please refer to http://en.wikipedia.org/wiki/Force for a discussion on force. Read the third example for a specific discussion regarding the sum of forces (vectors) being zero when an object moves at constant velocity.
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In the real world here is always a gradient, a perfectly flat road does not exist therefore the inertial forces are always in play.
Inertia and the force of gravity are not related, once again, rather than accepting what I say, please refer to http://en.wikipedia.org/wiki/Inertia
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It would ned to be measured but I do beleive that difference is insignificant when compared to the drag generated during calibration. Everything is relative to that point.
Agreed, it needs to be tested. In anecdotal tests discussed on CyclingForums, the difference has been as much as 30 watts, hardly insignificant in my mind.
Quote Quote
How much time will a rider spend on the tops of the bar when riding in a bunch?
How much time will they sond on the brake hoods where they can control speed more effectively and have more control?
I go with the latter, which is the recommended calibration position.
Over a 6hr ride is the time spent on tops of the bars significant to scew the power data? I doubt it.
Agreed, the rider would spend very little of the time on the drops, particularly in a bunch.
Sure weaknesses should be discussed for any item,but this should not be the focus of a discussion.
A purchase decision ismade for many reasons, but mosty cost / performance ratio drives this type of decision.
Also, the This-guy-on-a-forum-who-is-Mr X- in-his-field-and-therefore-must-be-right-and-has-no-vested-interest-in-my-decision says Item B is the best and therefore I want it is a common reason why often good products don't sell well.
Every Power meter will have drawbacks, whats important is that any user only uses one type of power meter to avoid variances in the design of each.
It's the change over time that is important,not the brand of power meter.
Absolutely agreed, it's just that the literature supplied by the product manager will never discuss the products weaknesses, only it's strengths - so there is plenty of that information available. Generally people like to use peer review as a process of understanding a products strenths AND weaknesses.
Yes, other power meters do have drawbacks, which have also been discussed plenty.
SRM - price and calibration issues, no altimeter
Powertap - one set of wheels for training and racing, no coded strap, no altimeter
Ergomo - price and only left leg measured and in my experience tricky calibration, difficult installation.
iBike - only works outdoors, vibration problems which seem to have been solved, smaller range of accurate operation
Polar - difficult set up, inconsistent power reading on big ring/sprocket combo, 5 second recording rate.
Product Pros:
SRM - recognised as most accurate, always on bike
Powertap - highly accurate, price competitive, can move between bikes.
Ergomo - good functionality - TSS, IF, NP, altitude, coded strap, comes with best software
iBike - very price competitive, easy installation, rich functionality, accurate if used and calibrated correctly.
Polar - cheapes of all, rich functionality - altimeter, coded strap etc.
#54
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Ultimate Hubber
Posted 14 December 2006 - 09:06
Quote
Quote
Every Power meter will have drawbacks, whats important is that any user only uses one type of power meter to avoid variances in the design of each.
It's the change over time that is important,not the brand of power meter.
What is important in measuring power is consistency of output - this is where the Ibike is most flawed - IMO there are just too many chances of inconsistent data for it to represent good value - especially when the price is comparable to a PT Std.
and you have scientifically proven this...?
BTW, my Powertap seems very inconsitent too. Seems to be affected by temperature...
#55
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Ultimate Hubber
- LocationCape Town
Posted 14 December 2006 - 09:20
This reminded me of you guys!
#56
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The awesome™ one
- LocationBloemfontein
Posted 14 December 2006 - 09:22
Simplicity is the ultimate sophistication.
Keep it single.
Keep it single.
#57
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Ultimate Hubber
Posted 14 December 2006 - 09:39
Quote
Quote
Quote
Every Power meter will have drawbacks, whats important is that any user only uses one type of power meter to avoid variances in the design of each.
It's the change over time that is important,not the brand of power meter.
What is important in measuring power is consistency of output - this is where the Ibike is most flawed - IMO there are just too many chances of inconsistent data for it to represent good value - especially when the price is comparable to a PT Std.
and you have scientifically proven this...?
BTW, my Powertap seems very inconsitent too. Seems to be affected by temperature...
Lefty I know it's hard but re read the post - when something is scientifically proven I will generally not preface it with "IMO" - "In my opinion"
But since you ask, there are numerous reviews out there that have all pointed to an inconsistency of readings due to one or more issues - if you are interested then you will find them.
I have never found PT to be temp sensitive - how do you know the inconsistency is down to temp ?
If you suspect this to be the case then send a few of the suspect files to Adrian at BPT.
#58
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Ultimate Hubber
Posted 14 December 2006 - 09:41
Bruce/Bikemax maybe you can help me?
On the powertap pro ,how long is the memory when it is set to the 2sec int?I am going away on a 5 day training camp and won't be able to take the laptop so I wanted to know if I should maybe set it to 5 sec?
And how does one clear the memory?I know there is a clr function but is that only for the current data or everything?
#59
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Ultimate Hubber
Posted 14 December 2006 - 09:46
nochain,
depends on the model of the computer. The ones I have, have a capacity of around 7 hours for a 1sec recording rate, so 14 hours I would guess.
I would not recommend increasing the recording rate more than 2 seconds, rather try make a plan to download the data.
Pushing and holding both buttons simultaneously until --clr-- shows clears the data but not the settings.
#60
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Domestique
Posted 14 December 2006 - 10:04
At R 4460 recommended retail price is'nt that nearing the price of PowerTap? What does the entry level PT cost?
#61
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Ultimate Hubber
Posted 14 December 2006 - 10:30
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At R 4460 recommended retail price is'nt that nearing the price of PowerTap? What does the entry level PT cost?
PT Std
R5299 or R5999 with wheel.
- Ibike , you have to add R700 for the cadence sensor and more if you want HR sensor.
#62
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Domestique
Posted 14 December 2006 - 10:33
Quote
Quote
At R 4460 recommended retail price is'nt that nearing the price of PowerTap? What does the entry level PT cost?
PT Std
R5299 or R5999 with wheel.
- Ibike , you have to add R700 for the cadence sensor and more if you want HR sensor.
So there's nothing in it from a price point of view!
