Power meters are all the buzz these days for cyclists and triathletes. It is interesting however that this buzz was first created by the cyclists and not the triathletes who seem to create a buzz about anything you could attach to a bike, shoe or body. We have several choices of power meters out there but the criteria to determine which one to get is the most difficult to establish. Do you go for scientific precision, cost, features, crank-based, hub-based, chain-based or none of these? How about weight? If I go with a hub-based system can I use my race wheels??
Such was the case when I first ventured into the world of power meters in 2004. Actually my first power meter was a Tacx Grand Excel stationary ergometer to which I still use to this very day. I can still remember finishing Grad school and seeing this amazing unit come to a local bike shop and how it would change my world forever - at least training and coaching wise. It was revolutionary for me as I could now train by power at home or wherever there was an outlet and not view the Human Performance Laboratories as the only place one could conduct experiments and fitness and performance tests. I was amazed then and now how much I learned from Grad school that I could actually use in the real world and actually build a career out of it.
So as you can tell, power meters have been an important training tool for me. Early on as I began coaching mountain bike racers and then road racers, heart rate was the training metric of choice for everyone. That was until I started testing my athletes and whoever was willing to come into my garage for weekend torture sessions. On Saturday I would conduct Maximal Aerobic Power (MAP) Tests (3min stages of increasing wattage until failure)on my Tacx unit and collected blood samples for lactate analysis to develop a metabolic profile of their fitness. On Sunday my boys and girls would indulge me in various time trials which ranged from 5km, 10km to 20km and I would calculate Critical Power and Critical Speed which further provided me a profile of each athlete. It was pioneering work for me and shortly after everyone saw dramatic progress every 8 to 12 weeks and finally gave in to my preaching on how training with power was the most effective means to prescribe training, many had gone out and bought their own units. It was fantastic! My programs were more specific and explicit than ever and no one could just coast through a workout.
My first mobile power meter was a PowerTap SL laced to a Mavic Open Pro rim. It was awesome! I used it everywhere and recorded every workout I could. When the unit broke on me out in a rain storm and I was without "power" for 5 weeks I was a mental wreck. It was at this time I realized I was a power junkie and I needed my fix. I did come to grips with not having the PowerTap and actually got to ride some wheels I had let collect dust and became reaquainted with my heart. What I had learned to realize was that I had learned how to read my training based on how my body felt during various training sessions which is a good thing because I now preach to all my athletes that if we striped all the power meters, heart rate monitors, cycling computers, GPS etc from our handlebars we still have to perform and we can still ride our bikes. The monitors teach us about our responses to training and help to calibrate our brain somewhat so that without the empirical numbers, we have a very precise sense of how hard we are actually working or performing on a given ride - good or bad.
As such, I have been wanting to share my thoughts on the iBike power meter. It is an amazingly complex computer given that it does not calculate power via strain gauges imbedded on a crank's spider or a rear hub. Rather it measures all forces opposing a rider such as wind, road slope, elevation change and accounting for the effects of gravity. Quite remarkable in fact. However, it is not quite useable out of the box as you must input personal data such as rider weight and bike weight to ensure accurate power readings. Then you must perform a series of roll down calibrations in a static position and then follow it up with a 4 mile calibration ride to set the slope and wind reading functions. By all acounts it sounds easy enough until the day you get out there and you need to find a flat to slightly uphill road o 0.4 mile in length for coast downs with minimal traffic, minimal wind, no gusting winds etc. Then you need a relatively quiet road 2 miles in length to do the out and back 4 mile calibration ride minimizing sharp corners where you need to apply the brakes. I have since found an area that works if the conditions are right and that is why it has taken a while to properly calibrate my iBike and collect data.
I sold my PowerTap a few years back and upgraded to an SRM crank-based powermeter as I wanted to use various wheels for various events and was not overly concerned with my crank choice. The SRM has always been considered the "gold-standard" in power meters but then again VO2max was also considered the "gold-standard" of one's aerobic fitness and that view has been changed too.
My intention for the iBike was simply to log training data when I would ride my road bike so I could have some quantifiable numbers from that bike for tracking purposes in WKO+ since I moved the SRM to my TT/tri bike. After calibrating the iBike (Gen II model), I put the SRM cranks back on the road bike for a comparison over several rides. Initially I was very impressed as they both seemed to report similar numbers early on. After a period of riding however, they would begin to dissociate from one another leaving me perplexed as to why this would happen. Velocomp LLP who makes the iBike seemed to have addressed my concerns and as I found out, the concerns of hundreds of other users with the release of the Gen III iBike. The new Gen III iBike has a ton of great features that the other power meters don't have. In fact I can upgrade the firmware on my iBike and turn it into an iAero which would lead to more potentially geeked-out things to do (http://www.ibikesports.com/products.html). This would allow me to use any other AnT+ Sport compatible power meter with the iBike computer head creating a real time wind tunnel-like tool.
This spring I was finally able to calibrate the Gen III unit and rode it with the SRM again for a week. What I found was that the SRM and iBike both show the same power profile when graphed together but the SRM reports higher values than the iBike does. I have tweaked the constant variables in the iBike software to see if I could get the two meters to report the same but I have since given up as it just doesn't work. Here is a comparison shot of iBike and SRM power data for the same ride:
At this point my only gripe with the funtionality of the unit is during cross wind situations as the wind port tends to be hidden from cross winds and as such does not report numbers deemed more appropriate for the perceived effort level. I experienced this as my SRM numbers jumped as I felt the increased resistance from the crosswind but the iBike numbers dropped as it could not collect the wind data. My second gripe is with all the addiiotnal costs of keeping up with the advances in the unit by Velocomp LLP. For example there is a new tube which looks like a Camelback drink tube but with a special connector that inserts into the wind port. This is apparently a solution for using the iBike on TT bikes and to help improve the collected wind data. The cost of this is U.S. $54 plus U.S. $40 for shipping. Ouch.
So does this mean that the iBike is not worthy?
The question has been answered most succinctly on the iBike forum by Boyd Johnson where he states something to the effect that there will always be errors in each of the power meters no matter their claims. I am confident in what he has reported in the following link; (http://www.ibikesports.com/techinfo.html). I have to say at times I have questioned whether or not my SRM is measuring my true output based upon my actual performances!
In summary power meters are invaluable whether they be a stationary trainer version or one of the mobile versions. Follow all set-up procedures carefully no matter the unit and pay attention to what you see in ral time and when analyzing the data in the software used. As long as the numbers are consistent in their reporting over the same or relatively the same conditions then you have a reliable unit and you can trust the numbers as they are personal to you. I would caution comparing with others as this can lead to false assumptions and outcomes.
JVD
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