Today pros are using power meters In training in increasing numbers. So what are they are how accurate are then?
There are many different kinds using several different methods.
The original method used was hub mounted power meters. These are approximately 1.5% accurate. This is a little misleading because that accuracy is for power delivered to the rear wheel without the losses in the legs, pedals, cranks, chain and cogs/sprockets. The hub alone is maybe $500 while the totally constructed wheel which isn't a wheel you might choose if you were buying wheels is about $1,000.
Lately they've been mounting strain gauges inside of cranks (one side or two) pedals or mechanisms that fit between the two. These are claimed to be 2% accurate. That too is a little misleading. Your legs are asymmetrical in power output so you would need two cranks with strain gauges installed to measure over a complete power stroke to get real accuracy and then this starts become an expensive proposition as well. You have the same problems with pedals and/or the interfaces that work with normal pedals. So again you're looking at around $1,000 or so to get a real power reading and that reading discounts all of the losses to the rear wheel.
I started designing a power meter that directly read the power. It did this using total weight, speed, frontal area, aerodynamic drag factor, grade, acceleration and wind speed. This seemed so simple that I couldn't believe that someone else hadn't done the same thing so went looking.
Sure enough they make a PowerPod that the bare bones model tells you most of the information you need to know. Now it appears that you have to have an higher level Garmin to get your data properly so that could be an added expense but the models go from about $200 to $500 with added features. The accuracy is claimed to be 2% but this is even more accurate than the hub since you wouldn't have traction losses to contend with though those are rather small.
Another company is attempting to break into the market and it is WattZit. This uses the same principles I outlined and since it is a work in progress it is pretty cheap. And a little crude. But it will interface with most smart phones so that $100 price tag to get most of the information you'd like is a steal. While the PowerPod has more advanced firmware installed and a set-up procedure that more accurately estimates frontal area and aerodynamic drag the WattZit isn't to that level of sophistication yet and they only claim an accuracy of 5%. Tell me - is a 3% real accuracy difference worth the $100-400 difference in the device itself and more if you must buy additional support devices?
As time goes by, I would expect the WattZit to become the power meter of choice of anyone but a pro racer. There was a noticeable difference when WattZit upgraded their Firmware from 1.1 to 2.0. The app that goes on your phone could certainly be improved but I use an older phone because it is small.
Now one should probably ask the question - what in the hell difference does it matter if you know the exact power that you put out? The answer is - probably none at all. Racers gauge themselves against other racers and not a device. Normal riders are only peripherally interested. If you train by yourself you could probably get as much or more real information from Strava. So unless you're one of those normal riders who have a passing interest in power output there isn't much reason to spend money to gain some information that you'd forget after the third use.
There are many different kinds using several different methods.
The original method used was hub mounted power meters. These are approximately 1.5% accurate. This is a little misleading because that accuracy is for power delivered to the rear wheel without the losses in the legs, pedals, cranks, chain and cogs/sprockets. The hub alone is maybe $500 while the totally constructed wheel which isn't a wheel you might choose if you were buying wheels is about $1,000.
Lately they've been mounting strain gauges inside of cranks (one side or two) pedals or mechanisms that fit between the two. These are claimed to be 2% accurate. That too is a little misleading. Your legs are asymmetrical in power output so you would need two cranks with strain gauges installed to measure over a complete power stroke to get real accuracy and then this starts become an expensive proposition as well. You have the same problems with pedals and/or the interfaces that work with normal pedals. So again you're looking at around $1,000 or so to get a real power reading and that reading discounts all of the losses to the rear wheel.
I started designing a power meter that directly read the power. It did this using total weight, speed, frontal area, aerodynamic drag factor, grade, acceleration and wind speed. This seemed so simple that I couldn't believe that someone else hadn't done the same thing so went looking.
Sure enough they make a PowerPod that the bare bones model tells you most of the information you need to know. Now it appears that you have to have an higher level Garmin to get your data properly so that could be an added expense but the models go from about $200 to $500 with added features. The accuracy is claimed to be 2% but this is even more accurate than the hub since you wouldn't have traction losses to contend with though those are rather small.
Another company is attempting to break into the market and it is WattZit. This uses the same principles I outlined and since it is a work in progress it is pretty cheap. And a little crude. But it will interface with most smart phones so that $100 price tag to get most of the information you'd like is a steal. While the PowerPod has more advanced firmware installed and a set-up procedure that more accurately estimates frontal area and aerodynamic drag the WattZit isn't to that level of sophistication yet and they only claim an accuracy of 5%. Tell me - is a 3% real accuracy difference worth the $100-400 difference in the device itself and more if you must buy additional support devices?
As time goes by, I would expect the WattZit to become the power meter of choice of anyone but a pro racer. There was a noticeable difference when WattZit upgraded their Firmware from 1.1 to 2.0. The app that goes on your phone could certainly be improved but I use an older phone because it is small.
Now one should probably ask the question - what in the hell difference does it matter if you know the exact power that you put out? The answer is - probably none at all. Racers gauge themselves against other racers and not a device. Normal riders are only peripherally interested. If you train by yourself you could probably get as much or more real information from Strava. So unless you're one of those normal riders who have a passing interest in power output there isn't much reason to spend money to gain some information that you'd forget after the third use.