BikeMax Posted February 15, 2007 Share Lets put it like this then - the Ibike is an indirect measure of power as opposed to a direct measure (such as SRM' date=' PT, Ergomo) In terms of Ibike being as accurate as PT when the calibration conditions are the same - the calibration conditions are a fundamental variable when riding (weight, draft, smotthness of road etc) and so this statement is largely meaningless when making a comparison of the two.[/quote'] You obviously don't get it. All of the power devices measure something and then calculate the power. Suggesting that there is indirect measurement for one and direct measurement for the others, is plainly incorrect, as in all the cases there is just the application of the laws of physics to different measurements.Weight will also not change meaningfully when riding, and draft is specifically catered for by the ibike. If you do the riding that you want to measure the power for using the same position as when the ibike was calibrated , it will give you as reliable results as a PT.I can think of enough reasons to rather buy a PT than an ibike, but accuracy is not one of them. Why not go and read the recent post by Bruce on the other thread - I certainly consider (as do many others) any device that measures strain/torque and angular velocity to be a "direct" measure and a device that measures the forces a rider has to overcome and then calculates power to be an "indirect" measure - we will have to agree to disagree. Weight can change by up to 4kg - say 2 water bottles and 2ks weight loss during a race - certainly possible and material I would have thought. How can you say that it will give as "reliable" information as the PT when there are well documented issues regarding draft (air flow), road surface etc that have a significant effect on power readings. Guys have reported up to 25% difference in NP over a ride of a few hours - this is not an acceptable variance. Do you never change position when training or racing ? I move regularly from hoods to tops to drops - wnat me to recalibrate to get an accurate reading ?? Link to comment Share on other sites More sharing options...
BikeMax Posted February 15, 2007 Share i) so you've bought an I-bike and tested it and it p*ssed you off and therefore it's rubbish to you? Or ii) are you merely regurgitating the outcomes of the "how do we handle the I-bike threat" marketing meeting held at CycleOp offices? Which is better?:Trek Madone SSLx or Time VXRS Ulteam? You really do have a vivid imagination GL.. Link to comment Share on other sites More sharing options...
wors Posted February 15, 2007 Share Jet aircraft use Ibike principals to tell them how fast they're flying' date=' how high, how much drag, how much thrust etc, etc so the principal is not new and Newtonian physics have been proven to be ideal for estimating performance of moving bodies in Planet Earth. [/quote']GoLefty, your logic is very flawed.Jet aircraft don't fly in bunches and the Newtonian physics thing is completely irrelevant.It's like saying that because the first astronauts used the stars as a primary means of navigation at one point then we should try to incorporate that principle in power measurement on bicycles too.C'mon if you are going to argue for one or the other keep it relevant. It actually is all about physics, irrespective of whichever power device you are talking about. And the effect of riding in bunches would only be relevant if you mounted the ibike at the top of your helmet or wherever you could where it would not feel the difference in wind speed. Sensibly placed on your handlebar, it will not be less accurate in a bunch. Link to comment Share on other sites More sharing options...
Le Tour Posted February 15, 2007 Share Go to: http://www.biketechreview.com/archive/pm_review.htmA review between SRM, PT and PolarIf you can get through the review (It reminds me horribly of my Engineering lectures) then a you don't need a power meter and should be able to calculate it in your head!! Link to comment Share on other sites More sharing options...
Brakkies Sport Fotos Posted February 15, 2007 Share "There is a common argument that as long as the unit is consistent, it is fine for training. Strictly this is correct, because what is of interest to an athlete is the percentage improvement over time, and not the absolute values"... this is from Bruce.. So if the ibike is consisted "in-consistent", it should be ok, because the difference is the value's you will use to see the improvement of your training program. Is that right? Link to comment Share on other sites More sharing options...
BikeMax Posted February 15, 2007 Share Jet aircraft use Ibike principals to tell them how fast they're flying' date=' how high, how much drag, how much thrust etc, etc so the principal is not new and Newtonian physics have been proven to be ideal for estimating performance of moving bodies in Planet Earth. [/quote'] GoLefty, your logic is very flawed. Jet aircraft don't fly in bunches and the Newtonian physics thing is completely irrelevant. It's like saying that because the first astronauts used the stars as a primary means of navigation at one point then we should try to incorporate that principle in power measurement on bicycles too. C'mon if you are going to argue for one or the other keep it relevant. It actually is all about physics, irrespective of whichever power device you are talking about. And the effect of riding in bunches would only be relevant if you mounted the ibike at the top of your helmet or wherever you could where it would not feel the difference in wind speed. Sensibly placed on your handlebar, it will not be less accurate in a bunch. I don't follow - the effect of air flow in a bunch and it's efect is well documented. How can an instrument mounted on the bars not read differently if the air flow is distorted by other riders ? Ibike have acknowledged that the device is not as accurate in small bunches or on a TT bike (due to air flow) Link to comment Share on other sites More sharing options...
MWdeJager Posted February 15, 2007 Share GoLefty' date=' your logic is very flawed.Jet aircraft don't fly in bunches and the Newtonian physics thing is completely irrelevant.It's like saying that because the first astronauts used the stars as a primary means of navigation at one point then we should try to incorporate that principle in power measurement on bicycles too.C'mon if you are going to argue for one or the other keep it relevant.[/quote'] I think everybody is missing the point/question. Will Pops benefit from iBike? From what I've seen with Marius's TRAINING sessions, is that he goes out on the road on his own and tries to find a piece of consistent road to do his reps. L1 so much, L4 so much, L2 so much etc. As soon as the wind is howling, he also has difficulty because the candance up wind becomes too slow and down wind too fast to train in his proper cadance zones. According the the Extreme Leftist, iBike will do just fine if these are the parameters to cope with. Personally I would just buy an indoor trainer that shows me my power but that's me. I'm happy to cycle indoors unless if I'm funriding. If pops wants to see his power figures from races where he was drafting a bit, pulling a bit etc, obviously the iBike will give results of varying accuracy. VA has some indoor bikes with power meters, but the forkin' things don't take cleats and I can't move the seat back - so I'll have to do without a power meter a bit longer... My 2c Link to comment Share on other sites More sharing options...
wors Posted February 15, 2007 Share How can you say that it will give as "reliable" information as the PT when there are well documented issues regarding draft (air flow)' date=' road surface etc that have a significant effect on power readings. [/quote'] Please give references. Link to comment Share on other sites More sharing options...
Brakkies Sport Fotos Posted February 15, 2007 Share "There is a common argument that as long as the unit is consistent, it is fine for training. Strictly this is correct, because what is of interest to an athlete is the percentage improvement over time, and not the absolute values"... this is from Bruce.. So if the ibike is consisted "in-consistent", it should be ok, because the difference is the value's you will use to see the improvement of your training program. Is that correct? Link to comment Share on other sites More sharing options...
BikeMax Posted February 15, 2007 Share How can you say that it will give as "reliable" information as the PT when there are well documented issues regarding draft (air flow)' date=' road surface etc that have a significant effect on power readings. [/quote'] Please give references. http://lists.topica.com/lists/iBikeProPowerMeter/read/ http://www.cyclingforums.com/t-341477-15-3.html You will have to trawl through them I am afraid as I don;t have the time to find the individual refs at the moment. Link to comment Share on other sites More sharing options...
GoLefty!! Posted February 15, 2007 Share Jet aircraft use Ibike principals to tell them how fast they're flying' date=' how high, how much drag, how much thrust etc, etc so the principal is not new and Newtonian physics have been proven to be ideal for estimating performance of moving bodies in Planet Earth. [/quote']GoLefty, your logic is very flawed.Jet aircraft don't fly in bunches and the Newtonian physics thing is completely irrelevant.It's like saying that because the first astronauts used the stars as a primary means of navigation at one point then we should try to incorporate that principle in power measurement on bicycles too.C'mon if you are going to argue for one or the other keep it relevant. It actually is all about physics, irrespective of whichever power device you are talking about. And the effect of riding in bunches would only be relevant if you mounted the ibike at the top of your helmet or wherever you could where it would not feel the difference in wind speed. Sensibly placed on your handlebar, it will not be less accurate in a bunch. amen. On the bars the wind speed will be less since you're drafting and therefore needing less power to keep up...I-bike should reflect this. Come on,.......this is drafting 101, first year cycling. Or have power meters suddenly changed Bernoulli's theorems as well.....**** you never know hey cos Heavier carbon bars can suddenly make a bike lighter at the scales too...saw it myself so it must be true.. Link to comment Share on other sites More sharing options...
BikeMax Posted February 15, 2007 Share "There is a common argument that as long as the unit is consistent' date=' it is fine for training. Strictly this is correct, because what is of interest to an athlete is the percentage improvement over time, and not the absolute values"... this is from Bruce.. So if the ibike is consisted "in-consistent", it should be ok, because the difference is the value's you will use to see the improvement of your training program. Is that correct?[/quote'] Yes - but it is not consistently inconsistent... The variances depend upon road surface, rider position etc and so unless you ride the same route in the same position every time then you may have a problem. Link to comment Share on other sites More sharing options...
Brakkies Sport Fotos Posted February 15, 2007 Share thanks guys, at least this fight was cycling related. Were do I get a better deal than the R4K from a fellow hubber Link to comment Share on other sites More sharing options...
MWdeJager Posted February 15, 2007 Share Vra die Extreme Leftist of hy nie syne op nog 'n PowerTap wil intrade nie. Dan hoef hy nie aanmekaar wiele/tyres om te ruil nie. Link to comment Share on other sites More sharing options...
Brakkies Sport Fotos Posted February 15, 2007 Share Just heard that you dont get the ibike saftware with, its a seperate package. You only get a 2 week trial period software to use. true? Link to comment Share on other sites More sharing options...
BikeMax Posted February 15, 2007 Share Jet aircraft use Ibike principals to tell them how fast they're flying' date=' how high, how much drag, how much thrust etc, etc so the principal is not new and Newtonian physics have been proven to be ideal for estimating performance of moving bodies in Planet Earth. [/quote'] GoLefty, your logic is very flawed. Jet aircraft don't fly in bunches and the Newtonian physics thing is completely irrelevant. It's like saying that because the first astronauts used the stars as a primary means of navigation at one point then we should try to incorporate that principle in power measurement on bicycles too. C'mon if you are going to argue for one or the other keep it relevant. It actually is all about physics, irrespective of whichever power device you are talking about. And the effect of riding in bunches would only be relevant if you mounted the ibike at the top of your helmet or wherever you could where it would not feel the difference in wind speed. Sensibly placed on your handlebar, it will not be less accurate in a bunch. amen. On the bars the wind speed will be less since you're drafting and therefore needing less power to keep up...I-bike should reflect this. Come on,.......this is drafting 101, first year cycling. Or have power meters suddenly changed Bernoulli's theorems as well.....**** you never know hey cos Heavier carbon bars can suddenly make a bike lighter at the scales too...saw it myself so it must be true.. If only it were that simple ... "DraftingI did one ride with two other riders, where I spentabout 40% of the time in a draft. It was apparent during the ride thatthe iBike was underreporting my power output in the draft by about40-50 watts. The pressure port should have accounted for the change inwind resistance, so why the inaccurate reading? My guess is that theiBike sits in the sweet spot of the draft, right at butt level of therider in front. Most of my body is catching more wind than the iBike,so I'm doing my work than it thinks I am, hence the low wattage. Theoverall wattage for that ride was 8% too low. I got in touchwith John Hamman of iBike and he confirmed this anomaly. He told methat it performs more accurately in a big pack, where the draft isbigger and more consistent. A couple of reports from message boardsback up that assertion" Link to comment Share on other sites More sharing options...
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