Buying a Power Meter....Options?

Here's something I posted in another thread a while ago:

Why measure power?
Power is a great metric because it removes many variables and gives you a pure number that can be compared across different rides. I correlate power with horsepower in a vehicle. A rider can go out and make 200 watts on 2 different courses. One course may be extremely hilly and 200watts may yield an average speed of 12mph. On the second course, the course may be much flatter and 200 watts may yield an average speed of say 22mph. The positive thing is the rider can look at both of these data points and know they produced equal amounts of power. The same goes for riding the same course twice, one day where it is VERY windy and another day where you've got a tailwind. Power doesn't care.

How can you measure power?
There are basically three main ways to measure power that I know of:

1) Hub based system (powertap). You get a rear wheel with a hub that contains strain gauges within it. Those strain gauges measure power and transmit the information to a computer (or garmin) by a wire (cheaper) or wirelessly (more expensive). Powertaps are the most common (only?) hub based system. The pros are it's easy to take a wheel off of one bike and put it on another (you'll also need to move the computer). This works best with a wireless powertap. You can move a wired one but you'll need to have wires for all the bikes (pain to remove all the wiring). The cons are that unless you're going to buy more than one or you're only going to race with it or only going to train with it, you have to commit to that wheel for training and for racing. This can be a problem for some people who have dedicated race wheels. You can buy the hubs individually and have a wheel built by your shop around it or buy a ready-to-go wheel with the PT hub already laced in.

2) Crank based system (quarq). Instead of having the measurement in the hub, you can have the measurement tool in the crank. Quarq is most popular I think in this arena. As far as I know these are always wireless. The pros are you can use any wheelset you want. The cons are you can't take it from bike to bike and they are pretty expensive

3) Other (ibike, polar etc). Basically company's like ibike and polar have come up with other ways to measure power. Polar has a thing that sits on your chain and attempts to measure power by chain tension. Ibike sits on the front of your bike and measure wind, etc and calculates backward power that is being outputted. These are cheaper but the accuracy isn't necessarily as good as 1 & 2. It all depends on what reviews you read as to whether they are accurate or not. I've heard people have issues with the ibike and aerobars as it needs a clear view of the road ahead.

Last thing is the computer. Most people already have a bike computer. If you want a wired powertap, you'll need to use another little computer display that comes with it. For wireless, powertap used to have a proprietary wireless system that would only work with their computer, in which case you'd have to pay them to upgrade it or use a second computer. That being said, newer powertaps and the quaq models are ANT+ compatible which means you can use them with computers that speak ANT+ like many Garmins (310, many of the edge models, but NOT the 305). Powertap makes their own computer as well but I don't believe Quarq does.

As far as interpreting and understanding power even better, the link below by the powertap folks is VERY helpful in understanding the basics, plus I think I already typed too much
http://www.saris.com/t-powerBasics.aspx

Hope I helped a bit...

There's also a new pedal-based powermeter coming out from Garmin

Hrm. If you have two sets of wheels, then you either need a crank based system or two hubs. With two hubs, cost becomes a bit steep especially with the rebuilding of the wheels, but something you could consider is getting a new set of "training" wheels with a PT, and a disc cover. A set of the new HED2 Belgium wheels, or DT Swiss wheels from wheelbuilder would be about $1600 with electronics and a wheel cover. Keep your race front wheel, and sell the race rear wheel to offset some of the cost.

Depending on what your race wheels and training wheels are, you could be looking at only a few hundred bucks out of pocket.

John

I was thinking of two options.

1) 2 hubs, bought used, one for the training and racewheel. Rebuild the wheels I already have and just go with it. My race wheel already has a disc cover, so that is taken care of.

2) Get a used, if possible, Quark power meter. Versatile regardless of training or racing. Only problem is that they run around $1600.

Current race wheels is a 808/1080 combo from Planet X. Only cost me $700, so by selling the set, I would not be loosing much, but it would be hard to find a cheaper wheelset of that quality (I love my Planet X wheels)

A third option, one I have not thought about, would be an iBike sensor. Uses an algorithm based on wind resistance and speed, things like that, and only costs $500 new. Any experience with that? Or is it not worth my time?

Not worth your time. Plus, it's useless on the trainer. PM's can still function on a trainer.

do the math. Find out how much an option like the one I described would cost, how much for the two hubs/rebuild option. Then make your decision. :D

John

Sell the rear+cover, keep the front, buy a kinlin/dtswiss rear with a PT and cover for races. Cheapest/best bang for buck solution and you'll be faster Crank pts are $$$$.

This would be my advice too and exactly what I did. Good enough to get myself and many many others to Kona. Call the guys at wheelbuilder.com. They will answer all of your questions but they WILL have a predisposition to powertap b/c that's what they do. I wouldn't wait for all of the vaporware out there.

Keep your race wheels and buy a Quarq..will be cheaper then selling race wheels, buying two hubs one in training wheel and one in race wheel. If you are set on race rear wheel this will be best way to go. If you are okay with running training wheel with disc cover keep your front, sell your rear and buy a rear with PT hub and invest in a wheel cover but it means taking it on and off between racing and training which some have no issue with others don't like doing as you have to take on and off your cassette and have to center the cover just so.

I had wired PT system in training wheel then bought wired Zipp 404s. Training wheel hub died so upgraded to wireless. When buying new bike opted to swap out crank that came with it for Quarq, and got new clincher Zipp 404s.

Having 2 different hubs can give you slightly different power numbers. My race wheels hub were slightly higher than my trainer wheel hub.

What kind of crank do you have? Is it compatible with Quarq like a Sram? If so you can send it in and have them replace the spider and it saves you paying for another crank.

I have to agree with Kathy. I would just get a Quarq and keep the wheels.

This user's post has been ignored.

Edited by PennState 2010-09-28 6:00 PM

I've got an iBike Pro...love it.  I used to have a PT.  The iBike software allows a comparison of a Direct Force Power Meter (DFPM) if you have both, like I did at one time.  On my first ride with both, my average from the iBike was 232W, same exact file but using the DFPM measurements was 229W.  Good enough for me.  So I sold the PT wheelset and now I don't have to worry about switching wheelsets and not having power.  Plus it's a lot lighter than the PT hub.

And the iBike software measures windspeed and shows you speed relative to wind...which is interesting. 

Hmmmm......

Not being able to use it indoors is an instant deal breaker for me, no matter the price. I went with new PT in a HED Bastogne and wheelcover instead of a quarq because I wanted the ability to swap bikes. I've gotta sell my rear race wheel which is sort of a pain but it's ok. My only complaint so far is swapping my trainer tire with a road tire since I'm in the indoor/outdoor transitional phase.

Edited by jsiegs 2010-09-28 9:07 PM

I use mine on the trainer all the time.  If you have a mag or fluid trainer there is an unlock feature that you can apply to the unit that will allow power to show.  I just use rollers and since both wheels are spinning my power shows up without any issues.