# Ibike power meter-an alternative to powertap?



## FSonicSmith (Jan 2, 2003)

I'm not in the business so please don't think this is some kind of shill advertisement. I did get a "Preem Cycling" catalogue (can't quite figure this outfit out either-they seem to advertise products but not sell them-for sales they refer you to the manufacturers website) which advertises a much simplified computer that will tell you everything-headwind, altitude, cadence, and POWER, with no special hub or crank. It just fastens to the bars and you install a typical fork sensor and spoke magnet. Their website is http://www.ibikesports.com/products.html. So the question; does anybody know how well this thing works?


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## xcmntgeek (Aug 24, 2002)

I don't think it could do it very well IMO because it is just an estimate, not an actual strain gauge reading. I'd bet you could get a used PT for just as much, and it would be much more accurate, and look a hell of a lot better.

J


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## Fast_C50 (Dec 8, 2005)

jury's still out if it's a "powermeter" or a "powerguesstometer"


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## FSonicSmith (Jan 2, 2003)

Before anyone corrects me, this thing does not report cadence.


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## palewin (Mar 12, 2003)

*Not a complete replacement*

Besides the open question about accuracy, it won't work on an indoor trainer, since it is designed to measure the forces acting against the bike (wind, acceleration, etc.) and none of those apply on a stationary trainer. So in that regard it is not a replacement for a PT or SRM which you can use BOTH indoors and out.


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## tigermilk (Aug 29, 2002)

Change position on the bike and oops, ibike does not give the right power (bases the power on coast down test --> calculates a CdA for that position and uses it for subsequent calculations).

Go from concrete to asphalt or chip seal or any other surface and oops, ibike does not give the right power (again, with a coast down test it calibrates for a rolliing resistance; change surfaces and that calibration is out of whack).

The jury is still out on whether it will work effectively in crosswind situations. Their test results are still in work and have not been released to the skeptical public.

If you are one who rarely changes positions or your positions are close (i.e., your torso angle doesn't change much whether you're in the drops or on the hoods) you may get decent estimates to within +/- 10-15%. It's more important that the device be repeatable than accurate though. If it's repeatable, it could be a good training aid.


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## Whareagle (Mar 24, 2006)

tigermilk said:


> Change position on the bike and oops, ibike does not give the right power (bases the power on coast down test --> calculates a CdA for that position and uses it for subsequent calculations).
> 
> Go from concrete to asphalt or chip seal or any other surface and oops, ibike does not give the right power (again, with a coast down test it calibrates for a rolliing resistance; change surfaces and that calibration is out of whack).
> 
> ...


The physics of this thing are tracking well in all conditions, terrain, and real surfaces. On several rides, I've been right on top of my Ptap for both accuracy and consistency. The Ergomo is definitely reading high by about 8%, btw, but the consistency is again, spot on.

I can't wait until I can get my FSA 2-piece cranks back on. <15lb. Soloist with power? Quite possible. 

Food for thought. They start shipping this week.


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## Coolhand (Jul 28, 2002)

Whareagle said:


> The physics of this thing are tracking well in all conditions, terrain, and real surfaces. On several rides, I've been right on top of my Ptap for both accuracy and consistency. The Ergomo is definitely reading high by about 8%, btw, but the consistency is again, spot on.
> 
> I can't wait until I can get my FSA 2-piece cranks back on. <15lb. Soloist with power? Quite possible.
> 
> Food for thought. They start shipping this week.


Hate to say it- but it AIN'T a powermeter if it doesn't measure torque. It's a fancy cyclocomputer at best (ala HAC4). Seeing the HAC4 is out now, and always available somewhere at clearance price (as the whole imputed power thing doesn't really provide what a real powermeter does).

If you want power, get a real power meter. That means SRM, Ergmo, Powertap or even Polar. 

If you want a overly fancy cyclocomputer- look at this thing or a HAC4. Honestly though IMHO both are a waste of money. 

:arf:


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## Whareagle (Mar 24, 2006)

Coolhand said:


> Hate to say it- but it AIN'T a powermeter if it doesn't measure torque. It's a fancy cyclocomputer at best (ala HAC4). Seeing the HAC4 is out now, and always available somewhere at clearance price (as the whole imputed power thing doesn't really provide what a real powermeter does).
> 
> If you want power, get a real power meter. That means SRM, Ergmo, Powertap or even Polar.
> 
> ...


(sigh). The physics of the misinformed. But you're right, the HAC4 IS a waste of money.

What IS Newton's 3rd Law again? For every action (hub, crank), there's an opposite and equal Re-action? Just change where you're measuring it. It's your choice what you ride, and how you choose to measure things, but Physics are physics, and the numbers we (they) have been getting are spot on for accuracy and consistency. IT WORKS. It works in different temperatures, it works in different terrain, it works in different weather conditions, it works in packs, it works in different body positions.

I do believe in SHOW, don't TELL, but this isn't the place and I'm not the person to allow that. However, that'll be coming soon, and you'll be getting other peoples' opinions besides mine. Maybe then you can make a decision. But keep your mind open. It's proper to be skeptical, but skeptically optimistic will get you further down the road. 

AMF.


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## Coolhand (Jul 28, 2002)

Whareagle said:


> (sigh). The physics of the misinformed. But you're right, the HAC4 IS a waste of money.
> 
> What IS Newton's 3rd Law again? For every action (hub, crank), there's an opposite and equal Re-action? Just change where you're measuring it. It's your choice what you ride, and how you choose to measure things, but Physics are physics, and the numbers we (they) have been getting are spot on for accuracy and consistency. IT WORKS. It works in different temperatures, it works in different terrain, it works in different weather conditions, it works in packs, it works in different body positions.
> 
> ...


There is a difference- I have been training with power for three plus years now. So _sigh_ right back- no torque measurement means imputed power, not real instantaneous measured power. What does every PM on the market measure-- torque. Otherwise is a variation of the HAC4 guessing game. 

I owned and rode a HAC4, and it wasn't a powermeter. From everything set forth here neither is this do-dad. 

You mention science but all I am seeing is salesmanship. Unless you can show me where you are measuring actual torque all I am seeing is an overpriced cyclometer. Now MAYBE if this thing sold for $99 or less and maybe if the claims of being a real power meter were clarified like with the HAC4. Otherwise I am still not seeing it. Just my $0.02.


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## asgelle (Apr 21, 2003)

Coolhand said:


> What does every PM on the market measure-- torque.


What about Polar?


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## Coolhand (Jul 28, 2002)

asgelle said:


> What about Polar?


As best as I understand it, it measures the torque on the chain itself by using a pickup. Kind of a two step process and one that is sensitive to set-up. 

Polar says:



> The system derives wattage from the chain, not from the crank or hub as other models do. The system works by measuring two key factors:
> 
> Chain Tension - measured using a sensor on the chain stay
> Chain Speed - measured using a sensor on the rear pulley
> ...


http://www.polarusa.com/consumer/powerkit/howitwork.asp

Given some mixed reviews, wouldn't be my first choice unless you already had a compatible HRM and were tight on budget.


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## asgelle (Apr 21, 2003)

The answer is right there in your quoted section. The polar measures force on the chain (tension), not torque. 

And the qustion is whether all power meters measure torque, not the advantages or disadvantages of any one design.


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