Power meters

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.

 

"Racers gauge themselves against other racers and not a device."
I guess you've never watched Chris Froome on any major climb. He watches his power output like a hawk, as he knows exactly how many watts he can sustain for a given time. Although other riders aren't as obvious about it, they're increasingly doing the same thing.

My girlfriend has had a PowerPod for 3 seasons. While it certainly works, the constant re-calibration it does results in readings that are only consistent after the first 10-15 minutes of a ride. It reads higher than her TACX Neo Smart trainer, which is known to track very closely with other power meters. It's susceptible to anything that affects the airflow to it, so it has to be positioned away from cables and the angle of the unit must be consistent. Unfortunately, the mount has some play in it, so if you take it off, unless you're careful, it's easy to put it back in a slightly different position. Overall, she's happy with it for the price, but any claims that it's more accurate than other power meters are suspect at best. As long as one is aware of it's quirks, it will provide consistent data, which may be more important than accurate data.

"WattZit"? What an unfortunate name; it sounds like an acne medication! Hopefully the product is better than the moniker. Checking out their website, it looks like Tom wrote it, as it's full of typos. The unit itself is a bulky, ugly black box. It requires a spoke magnet, because it can't connect with bike computers to obtain that data. Overall, it seems more like someone's basement project than a finished product. Good luck to them selling it retail.

 

I went back and watched the demo and installation videos. At one point he's going downhill, slowing to a stop and the power reading is rapidly fluctuating between 25 and 600 watts! Yeah, that's really some kind of accuracy!

Hey Tom, did you notice that he's riding tubulars? <gasp>

 

Brian, if you go to the PowerPod website and look at what they have to say is that they've slightly redesigned the pitot tube because they were getting water into it which caused wild variations in reported output. This doesn't require riding in the rain but simply washing your bike and accidently splashing some water on the pickup.

Is there some reason for you to believe that strain gauges are more reliable than this PowerPod over time? Or do you have a set of cranks that cost a fortune and a lot of hopes and ambitions?

I couldn't care less what Chris Froome is doing - if he is watching his power meter and the group rides away from him he either goes with them or loses. I did not see Geraint Thomas looking at a power meter. I saw him looking at the competition.

 

By the way - concerning tires. That picture of who-ever's TT bike showed him using Roubaix tires. Specialized's TT tires are the S-works Turbo. The Roubaix has so much rolling resistance that they don't even bother to publish their levels.

Vittoria tires have the lowest rolling resistance and are FAR less than the competition. And the Vittoria Corsa Speed clincher has 15% less rolling resistance across the board from the Corsa Speed tubular. What you appear to be saying is that you're willing to throw away a 15% rolling resistance advantage in order to look like a Pro when you don't even know what the Pros actually ride.

 

I wasn't even talking about the PowerPod, I was talking about the WattZit that you were so excited about. Pay attention for a change.

I have no idea and made no claim either way. That wasn't even part of the discussion.

 

Brian if you mean one installation and setup video at least have the good sense to say which one. ALL of the power meters have setup videos. Don't act as if I'm crazy because you're inaccurate.

I am an electronics engineer and programmer. I am not bothered by firmware problems during early releases of stuff when it is a simple download to fix it. Looking at the installation video it looks like some pre-release firmware. Exactly what would lead you to believe that would be anything other than a glitch in the firmware? This guy is working out of his backroom and has to market these things as he can. It measures ALL of the necessary factors to make it a workable power gauge so if the firmware needs improving then he can get to it.

Would you rather pay $99 for something that is 5% accurate or $2,000 for something that is 2% accurate?

I should add that your daily changes in condition both up and down depending on your amount of sleep and breakfast and just general feelings are probably +/-10%

 

If you could manage to focus on a conversation, it would have been very obvious which power meter I was talking about.

I really don't care about the nature of the errors, the point is that this is little more than a glitchy prototype at this stage and it needs a lot more development.

I wouldn't pay $2000 for any power meter, but I might spend $200 for something like a PowerPod, which actually works, consistently, if not perfectly, unlike the WattZit. Remember, YOU were the one extolling the virtues of the WattZit, not me.

 

So tell me how you know that it's glitchy or not consistent? From a youTube video made at the outset by an engineer who doesn't have the slightest idea of how to market things and how people like you are willing to jump to completely false assumptions with no more experience than a video?

I will repeat - since you do not own one, you have not used one and everything you say is fomented by a cheap video you are passing out nothing MORE than an opinion. And a false one at that.

 

No Tom, I'm simply observing what I saw in a video produced by the manufacturer of the WattZit. I didn't make anything up and it's quite obvious that it has issues.

It's also quite obvious that you have issues.

 

Actually what you're saying is "I don't know anything about this power meter. I am not an engineer. I don't know anything about power meters and now they operate but I didn't like the initial video showing how to set up the device."

Well, I must say you've been pretty effective at making your point.

 

Frankly Tom, I don't care what you think and I'm sick of your made-up BS. From now on, we're just going to post the following warning whenever you start a thread, so that you can't hurt anyone with your inaccurate nonsense or suck anyone into another pissing contest:

"For anyone reading the above post from "cyclintom , do not take his word for anything, as he frequently posts inaccurate or misleading information that could be potentially dangerous. Make sure that you double-check everything using reliable sources of information before making any decisions that could result in physical or financial harm to you or anyone else. We don't think he does this maliciously, he simply doesn't know what he's talking about and refuses to listen to anyone who attempts to correct him, so don't waste your time. Unfortunately, he seems to be a lost cause."

Beyond that, I'm done with you. Have a nice life.

 

As with the rest of your postings, that says a great deal more about you than it does me.

 

To give some more information: I bought a WattZit and tried it out. Damned if I could get anything that even faintly resembled an accurate reading.

I think that I'll get one of the new generation PowerPods. This may turn out to be as Brian says and only work for awhile but PowerPod themselves admitted to the problem Brian was talking about and said that it was due to water in the pitot tube. That they had redesigned the pitot so that it would self drain.

I don't believe that paying a small fortune for a set of pedal or crank mounted or even a hub mounted power pickup would be any more accurate than a pitot with an accelerometer and an altimeter.

 

Tom, go back and read post #2 in this thread. I never said that the PowerPod "would only work for a while", I said that it recalibrated itself for a few minutes at the beginning of every ride, so you get some data that's not accurate initially. I wouldn't expect it to work well - if at all - in the rain, due to the fact that it uses a pitot tube.

 

I guess I don't understand what you mean by it "recalibrating itself".

 

Go to their website and check out the documentation. There's a specific calibration procedure when you first install it, then it recalibrates - or refines the calibration - based on the data it receives during the beginning miles of each ride. In many cases, you don't get accurate data until that process is complete. That's just the way it works.

 

Probably, more importantly - did you think you got acceptably accurate data from this thing. The WattZit is just about worthless with it varying from zero to 1000 during rides on flat ground.

 

Yes, once it settles down, it seems to be pretty accurate, but we have nothing to compare it against. It's at least consistent.

 

Precise accuracy probably isn't as important as reliability so that you know that an increase today is an increase and not some change in calibrations error.

It turns out that I just had an abscessed tooth that has turned into a money pit so It will be spring before I can do anything in the way of power meters.