New to Power Training

[MontyM]

Well, tomorrow I start training with a coach. I'm excited about it. Blood tests and all. My lactate will be measured and a training program will be recommend.

I will be training based on watts rather than heart rate. This will be new to me, I always uded my heart rate as a guide. I have a Computrainer, so for indoor training I will be ok. But, this spring I will be needing a power meter. An ibike looks like a good choice.

Now come the questions that you all have heard over and over...

How do the power reading compare to direct measuring methods. Do varying road surfaces effect power reading (paved, blacktop etc) or is this insignificant . How about different riding positions?

Thanks
MOnty

[travispape]

Hi Monty,

Here's my 2 cents. (I've actually never had occasion to check in on this subject before.)

The iBike has very good sensors and firmware and I think you will find that it provides the accurate numbers you need for your power training. Each of the power meters have their pros and cons and each can have problems that cause inaccuracy. A strong point of the iBike is that all of its analog sensors are fully contained in a small, light package that rarely breaks. (The external wheel & crank counters are digital--as long as they are communicating to the iBike, they are competely accurate.) In comparison, the drive-train-based power meters are by necessity much more complicated mechanically and subject to stresses that the iBike doesn't have to get mixed up with.

As you point out, a trade-off is that the iBike calculations can be affected if the rolling resistance or aerodynamic conditions during your ride vary significantly from the conditions you had during your calibration ride (coastdowns & 4-mile ride). At the pace that most iBike users ride, the aerodynamics are more important so that most road surface changes in real riding conditions get "washed out". Most of the time in real conditions, you will find that changes in rolling resistance are not detectable in your data.

Regarding the aerodynamic factor, yes, if you set up in a bad aerodynamic position for a long time when you are trying to ride 20+ mph on a flat, that will screw up your power data; however, riders just naturally don't do that. When the aerodynamic conditions are most important, riders naturally take their aerodynamic position. As long as you hold that position when you do your coastdowns & 4-mi ride, you'll get accurate results. Sitting up or standing on a hard climb when you are putting almost all of your power into overcoming gravity does not have a significant effect on your power data since the aerodynamic losses are very small during such climbs.

As you search around, I think you will find that user experiences with the iBike almost always bear out the accuracy of the iBike.

Also, keep in mind that the iBike logs a ton of other data for you that the other power meters don't. There are a couple of options for getting elevation data; however I don't know that any of the drive-force-based power meters are providing slope (accelerometer measured) or wind data.

One more point to make is that you have the option of factoring a second CdA (aerodynamic resistance) factor when post-processing your ride on the PC. If you find that you normally set-up into a less aerodynamic position below a certain speed, you can factor that into your ride data later in the iBike 2 software.

I'm not putting down the other guys. They charge more and usually provide accurate power data. The iBike provides a lot more data for a lower price and most users find that the power data is just as accurate.

Travis

[leonsrocketcar]

One very impt factor about the iBike that seems to go unmentioned when iBike associates pitch the product is: EXCELLENT CUSTOMER SUPPORT!!

Go look for a forum for the other PM mfg: none

Go look for instant call back, email support from other PM mfg: none

Sure some people get offended by Richard's directness (I don't), but he responds way too fast for a guy who coaches full time and supports other initiatives too!

Now my two cents: I find the iBike to work rather well for my training alone. But when I group ride or race, I don't feel I can rely on the data because of the drafting. My PE is zone 4, but my power output in a draft is L1. Granted I don't spend time staring at my iBike when it is time to put the metal down, but when I am at the PC reviewing data I just don't see what I felt. I ride with alot of PT and SRM dude/dudettes, and considering the cost of those units (and the fact that I want to keep my REDS and rovals) I feel like I could use that money to get me a TT bike and move my iBike between the 2.

I guess I am trying to say match your pocket book with equipment needs/wants vs. what you expect to do with power. I prefer to put money into frames/components rather than 1 powermeter on a clunker going up a 15% grade in the middle of summer

[racerfern]

But when I group ride or race, I don't feel I can rely on the data because of the drafting. My PE is zone 4, but my power output in a draft is L1.

Right about here is where I get confused. Obviously hanging in the middle of a large group cuts your power needs dramatically. There is nothing like taking 10mph off the wind to help anybody along.

However traveling a flat road at 22 mph in a headwind that has been cut by a group is still a significant workout. I don't see where the iBike falls short in this scenario. In my condition I can only maintain 22 mph in good headwind for a few minutes. My output might be in the 300w range. With a group my output drops to the 175w range and I can maintain substantially longer. Why would the data gathered in a good draft be more susceptible than riding alone?

[travispape]

I think that you are both right about drafting.

Why would the data gathered in a good draft be more susceptible than riding alone?

Disclaimer: This is my own personal speculation on the matter without any data yet:

In a single file pace line, the iBike unit is generlly in the sweet spot of the the draft--namely, behind the butt of the guy in front of you. Most of your body is too; however, some of the bike might be in a less efficient portion of the draft--getting more wind exposure. Therefore, the iBike might slightly under-report power in a single file pace line. If it does under-report power, it shouldn't be by large amount. Both you and your bike are getting the benefit of the draft--the only question is how uniform is that benefit from the road surface up to your helmet.

We intend to get some data and address this issue in the future, but we are working on other things right now. Once we get some pace line data, we might very well find that Fernando is right and that the lower power reported in a pace line is still accurate and there's nothing to adjust. If we do find a need to adjust power in a pace line to compensate for a non-uniform draft profile, we'll provide a way to do it. As you've seen, we've provided lots of additional tools to existing iBike customers and those are going to keep coming.

Note that in a peloton that the draft benefit over body and bike is much more uniform and you would expect the iBike not to have any problems associated with a non-uniform draft profile.

Travis

[Steve_Davidson]

My thoughts Travis are that the ibike does under report power in a tight paceline (depends on how close you are, relative size of the other riders and wind direction) but is OK in the middle of a large bunch. In certain situations like a fast double paceline there can be a fair degree of wind buffeting from other riders and echelons can give quite large variances in pressure that the ibike senses and maybe your upper body doesn't.

I got round most of these problems using a little intake vane on the ibike made out of a small piece of plastic. The ibike works better with the vane in cross winds and in blustery conditions and it doesn't affect operation in normal conditions.

[leonsrocketcar]

Apologies if we are stealing the intent of this thread, it is just that the subject of iBike data vs my perceived efforts have me confused at times. None of us are saying the iBike is putting out under reported data in pace lines. The comments above are a nice start and as Travis said, they have the subject on the to do list for 2008, I hope