Haastrup

Hi,

Has anyone tried this new powermeter and is it any good?? I can't find anything about it on the net so I'm very interested in hearing some comments about it.

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pinky

Well it just was introduced at interbike so yah you're not going to find much, but buy a real power meter not something that measures everything else then infers your wattage...

zero

It looks like it is built around the same principles of the HAC 4, which is very inaccurate in terms of power measurement. I'm just going to wait until I save up enough to buy a PT

doctorSpoc

they don't seem to be revealing too many details on how this thing works, but from what i can gather the take speed, wind pressure, weight, gradient, acceleration etc and turn that into a power reading.

But i can't see how that can be anything but a VERY crude estimation because in most cases the majority of resistance to forward motion comes from wind resistance of the rider. but every rider is different even if they weigh the same, and this changes with the size of the rider, their position... how much he or she is tucked, what they are wearing etc. so i can't see how this can be accurate at all?? the only thing they seem to be using to customize the reading to the rider is his or her weight but me an someone else may have vastly different positions on the bike and even one person may have different power reading based on their position at any given time during a ride so the power reading have got to be way off in certain situations... the other features seem pretty cool but for power reading i think you better look at an SRM, PT, Ergomo or even the polar... as expensive as they are.

2Rodies

There was a post about this unit about a week ago on the Texas Bicycle Racing Association website by someone involved in it's development. It's based on windspeed/bike speed to determain watts so it isn't very accurate. If you want accurate measurement you need a PowerTap/SRM/Ergometer. These devices are not cheap but they do what they promise. I used a HAC (which is simular to this unit) for years, when I got my PTP I used them side by side and HAC was reading over 50% different than the PTP. I've done side by side comparasons with my buddy and his SRM and the PTP is within 2 watts of what he getting.

Corsaire

Cut to the chase in your search and buy the real thing:

www.srm.de

Gotta shell out the bucks though at over $ 3,000.00

Corsaire

2Rodies

Don't rule out the PTP for the same price as the base SRM you can have the PTP w/Zipp 303's. For 3k you could have 404's.

Advantages of the SRM you can use any wheelset which means you can have it durring your races. Disadvantage cost, 80% more than a PTP and no more accurate. I got my PTP used (barely) for 450 with a second bike kit and a Mavic CPX33 rear wheel. This is an unusually good deal but I see them all day on ebay for under 1k.

kyzyl2

The HAC4 uses a barometric pressure sensor to detect altitude changes and from that they try to figure the watts used in climbing hills. However, everybody knows that baro sensors are slow to react (you gotta climb 100 feet before it even registers!) and worse yet, baro sensor altitude measurements fail completely when the weather changes. So, there's a real issue with hill power accuracy.

Also, the HAC4 doesn't measure wind speed, so it can't measure aero power.

It has no way to determine rolling resistance.

In short, it's not surprising the HAC4 has accuracy issues.

The iBike guys say they measure elevation changes using a completely different sensor--an inclinometer--that is very sensitive and fast.

Their website photo shows a pressure gauge at the front of the product, so quite clearly they're measuring wind.

Their FAQ section says they measure aerodynamic and rolling resistance drag coefficients, so they're accounting for those factors.

We haven't seen the tests yet, but it seems like they've thought about all the issues and they're claiming they have accuracy comparable to the expensive power meters.

Maybe they're on to something.

2Rodies

There was big disscussion about this on the TXBRA website and several engineer types were involved, including someone from this company. The problem is that way this unit is calculating your watts doesn't include direct force on the pedals. The SRM and PowerTap units do. This unit may be more accurate than a HAC or Polar unit but it still a far cry short of the other two.

kyzyl2

I suggest you spend some time looking carefully at their website, www.ibikesports.com. They have a video that explains how the iBike works, and a pretty big FAQ page.

Among the things their website explains is that Newton's Third Law requires that the forces applied by the cyclist on the pedals MUST exactly equal the forces opposing the cyclist's forward motion. The iBike accurately measures the forces opposing the cyclist's forward motion. That fact, in combination with Newton's Third Law, is why the iBike achieves accuracy comparable to high-end pedal-force power meters.

doctorSpoc

but they don't ACCURATELY measure the forces opposing the cyclist's forward motion... by FAR the largest force opposing a riders forward motion is the riders drag... the ACTUAL riders drag... not some approximation of some generic rider based on wind speed and rider weight but the actual riders, actual drag... it doesn't do that so, it absolutely, 100% cannot be accurate, we know that for sure. by chance under certain circumstances it could be accurate if the formula they use to APPROXIMATE rider's drag by chance equals your actual drag. but even so a riders drag is quite variable if one day i have my skinsuit, timetrial bike, Zipp 808's and i'm in my ultra tuck vs. another day when i'm out on my road bike not really tucked that good and wearing a loose fitting jacket.. my drag on those two days would be WAY different (i'm guessing as much as 30-40 watts... 15%) and this device would/could not make any adjustment for that it would happily give me the same reading one might be close one would be way off.. it doesn't know my position, my body type, what i'm wearing, what equipment i'm using... in fact, just by going into a good tuck vs. sitting up a bit more will change my drag quite a bit. if i'm in a crosswind with aero rims and bladed spoke vs. low profile rims and spokes... the list goes on... the fact of the matter is that this device just cannot be accurate in the real world it's impossible... Newton's Laws hold, it's just that they cannot accurately measure the bulk of the opposing forces accurately.

DannoXYZ 

However, there's absolutely zero way the device can measure "the forces opposing the cyclist's forward motion". That's primarily wind-resistance and there's absolutely no way it can determine how big of a hole in the wind the rider is blocking. It may know the bike's speed, even wind-speed to account for head & tail-winds, and elevation changes, but it doesn't know about Cd*Ca in order to come up with total wind-drag, nor does it know the rider's weight, which makes a difference in power-to-speeds going up a hill.

Sure they know the power equation:

power = force x speed ; (actually speed=distance/time)

But how are they measuring that force? They're NOT, they're making guesses and calculations without actually measuring force. I'd be surprized in a simultaneous comparison with an SRM or Powertap on the same bike that the iBike would anywhere close to within +/- 10% of accurate compared to something that measures actual force at the pedals or hubs directly.

Here's a quote from their website which sums up the inaccuracies:

Here's a test, ride fully upright at 25mph and it will read out a certain power-output. Then drop down into the tightest tuck you can and maintain the same speed. It WILL read out exactly the same power-output even though your legs will tell you that it's requiring 40-35% less power to push you at that same 25mph. There's absolutely zero way the iBike can tell you've just cut your Cd*Ca drag by 20%.

2Rodies

Newtons third law not withstanding how would this device account for the fact that I'm doing big gear spin ups. For example the force I'm putting on the pedals when I start from say 10mph in a 53/11 at say 40rpm and spun up to 90rpm. Wouldn't the watt's and torque generated at the lower rpm's be greater than at the higher rpms? My PTP shure says so.

doctorSpoc

DannoXYZ - the rider does enter his/her weight into the unit so it actually should do a decent job at calculating power going up hill especially since the speeds are lower so drag is less of an issue... except how does it know how much water you have on board

2Rodies - the unit should be able to detect if the rider is accelerating and at what rate and it knows the riders weight so it should be able to account for that...

the only thing I see this unit cannot do is calculate a rider's/bike's drag... the real problem with this is that this is the single biggest opposing force to the cyclist's forward motion

another quote below... this is pretty bad... it's really missleading because the other manufactures give accuracy for instantaneous measures while these guys give it for the duration of a whole ride?? how does that help me?? if i'm looking at my power meter i want to know what my reading is right now so i know if i'm doing the workout i'm supposed to be doing... my ave power for the duration of the ride is nice but it's not going to help me get my workout done properly... so in terms of instaneous measure like eveyone else does it... a 7.5% accuracy while a PT, even the cheapo one has an accuracy of 1.5%... but in reality this iBike meter is going to be off way more than 7.5% in certain instances... try 15-20%

"Let's suppose that the rider is out of his normal riding position on the hoods and that this is causing a 10% underreporting of aero watts. The iBike Pro would be reporting 200W instead of 215W. The total wattage variance at this particular instant of the ride would be 215W/200W = 7.5%, not 10%, and only for that portion of the ride. If the iBike is off by 7.5% for 10% of the time due to riding in the drops, the net error over the whole ride is only 0.75%. That's less than 1% and is well within the accuracy range of competitive products." WTF??

cosmo_the_third

Dude, worst thread ever...

kyzyl2

This is a very old and out-of-date thread. In fact, every posting made here was written in 2005, at least 8 months before the first iBike shipped in mid-2006!

To get current (and fact-based) information and comparative data about the new iBike Gen III (December 2008) please visit [removed by admin]

Racer Ex 

Great video on the IBike:


Bloody viking.

Juha

kyzyl, welcome back.

Just asking: you registered back in 2005, seemingly just to post in this one thread. Now, after a three year hiatus you post again - in the same thread. Are you somehow connected with ibikesports?

--J

MDcatV

thread is 3 yrs. old, what makes you think anyone was looking for it?

Racer Ex 

My video link explains everything.

Doggus

The accepted method of spamming these boards is to hire an army of shills - see BikesDirect model for an example.

Now send me one of them gadgets and we'll get the process moving. I'm for sale.

kyzyl2

Yes, I work for Velocomp.

I made this posting because this thread shows up on web searches for the iBike and I wanted to be sure that visitors to the thread knew that the iBike had changed considerably since these very early postings!

gsteinb

lock it

bdcheung

botto