Power Meter: What's the Best for the Money?

I want to start looking for a good power meter, but I don't want to shell out a lot of money and then be disappointed or wish that I had waited and bought something better.

Does a power meter hinder riding speed in any way, like by being very heavy or by causing some kind of resistance while measuring power?

Which power meters are the best deal? Assume that you have a computer at home and you can download workouts. I'm guessing most people on this forum have computer access. Otherwise, you probably wouldn't be here.

Are there some features which are overkill and not really needed?

Do some have wireless capability which enables on-the-fly downloading to the internet? Maybe someone could watch your progress at home this way, if they wanted to.

Any and all comments about power meters are welcome here. Let's learn what we can so we can make an informed purchase.

The best is the SRM power meter (well it has lots of other functions.)
The most value for money is the Polar.(also with lots of other options)
The srm is heavier than the polar. But apparantly light enough for several tour riders to be using it.
The SRM is overkill unless you are an proffessional athlete or aspiring to be one.
Both offer a wide variety of software and data that you can use in your training.

There are also two models by CicloSport that offer a "virtual" power reading. The HAC4 and the 434 both have this feature. The HAC4 has something like 50 functions (and is currently in use by the USPS team), where as the 434 is more of a standard bike computer with altimeter. Both units provide this "virtual" power reading by programming your weight into the unit, and then it used your speed and rate of incline/decline (maybe the HAC4 uses cadence as well?). These seem to beat most other power meters in price at about $150 for the 434 and $300 for the HAC4--but obviously don't give the accuracy that the others can provide.

Jeff

Do they all compute power using the same principle? How does this work? I already know it factors in wind somehow. I understand that it measures torque. I wonder how it does this. Is it by measuring differences in the conductivity of the metal under stress? Does it ignore this and instead measure variances (fluctuations) in spin? I wonder how accurate these meters really are? For example, if it says you are generating 305 watts, do you suppose it is accurate to within say 1%? I wonder if you would get virtually identical readings on different bikes.

Actually, I didn't know they used power meters during the Tour. I thought they wouldn't because of the edtra weight. Perhaps this is insignificant compared to the benefit they get from them. I suppose this is how Voeckler so carefully navigated the Pyrenees and kept the yellow jersey. Maybe he knows his red line on the power meter, and he just kept it right below that to keep himself in the race.

Actually both the CicloSport units are not much larger than the standard bike computer. The ONLY factors these two units use to compute your power are your weight, your speed and the percentage incline/decline (which is a function of the altimeter), and possibly cadence. Therefore, the CicloSport models do NOT factor in wind resistance at all, making them the most unreliable that I know of (compared with the other power meters available). The Polar unit uses a measurement of the stress on the chain I believe, the SRM unit incorporates the crankset (not quite sure what measurements it uses), and the PowerTap model uses the rear hub to make its measurements--all of these will take wind resistance into account, since they will measure cadence, speed, altitude (incline/decline), and gearing, as well as the stress on a part of the bike (chain, hub, crank). From everything I have heard and read, the SRM is by far the most accurate but also the most expensive. The PowerTap model requires a new rear wheel (since the main piece of it is the hub), and is in the same price range as the Polar unit (assuming you don't already have a Polar S710i or above). I have only had minimal experience with the CicloSport 414 (an older model very similar to the 434).

Jeff

Hmmm. Here's a comparison study that appears to be dated almost a year ago. I don't know if products have since then improved. It mentions the ergomo sport, as well. I wonder how good that one is.

It looks like the meters are weighing in at about 3/4 pound (300 gm range). It dawns on me now that the Tour de France racers may be able to include this number in the weight of the bike to stay above the minimum requirement. If that is the case, the additional weight would be zero from this component because they can then simply reduce the weight of the rest of the bike. I have a feeling this may not be the case.

Anyway, they list that SRM at $2,300 and the Ergomo Sport at $1,279. That's a lot of money either way, but these prices may have come down some. It probably has been a year now. Maybe there is a newer model.

I don't know that I would want one that doesn't take into account the wind. That seems like it would be off too much. If it's a good meter, it should measure accurately the power delivered to the ground from the tire. If you wear aerodynamic clothing, the readings will be lower at every speed than if you wear street clothes or ride into the wind.

Maybe this report is rather biased given that the readings from Ergomo Sport are provided by the company itself, but it seems to suggest that this Ergomo Sport is the best product at almost half the price of the SRM Pro.

Have you heard of Ergomo Sport?

http://www.ergomo-usa.com/head2head.html

Jeff, the Hac4 power meter does not use cadence as an input because the cadence kit is optional and the power meter works even without the cadence kit. It is not entirely true that the Hac4 does not factor wind resistance - it DOES factor wind resistance, but it assumes that there is no head, tail, or cross wind. In other words, the less wind there is, the more accurate it is. If it didn't factor wind resistance, it would be worthless as it would always say that you were exerting basically no power unless you were accellerating or climbing (because wind resistance is almost the only force on the rider on flat terrain).

I wonder if it would read a higher number if you put glue on your tires or heavy tar. I'm not joking around when I ask this. I simply would like to know the mechanisms involved. I wonder if the computer feeds back and assumes a certain wind resistance based on ground speed, which would be the speed on the speedometer. If you have a tailwind, it would overstate the wattage. If you were riding through sand on the beach, it would understate the wattage.

But maybe that's not how it works. Hmmm.

This is not how it works. There are no other sensors except for the speedo that it would use, so it would not know if you had sticky tires.

BAM - this is how it works. It assumes that there is no wind, it uses your weight as an input (bike + rider = weight), and based on this, it uses some sort of resistance constant (based on average wind resistance of average bike, average rolling resistance, etc.) to calculate the power output. This illustrates the weakness with this type of meter - we know that if you put on aero bars and deep section wheels, and emptied your water bottles, you would use less power holding your speed and gradient constant, but the Hac4 would tell you that the power output is the same. Same problem for wind resistance, except that on average, the wind resistance plusses and minuses balance eachother out.

somebody's gotta ask:

you are not quite sure what it does or how it works,

BUT, you are interested in a $2500 data collection system for your bike?

He was asking about a Hac4, which costs less than $350 on ebay and it includes all the other ciclocomputer features, heart rate monitor, etc.

he asked for a "meter", not a crystal ball.

for $350, i will be glad to tell him how i "think" he's doing.

Will you also sit on his bike, tell him his speed, altitude, heart rate, and cadence, then download all this info to his computer and turn yourself off until the next time he rides? If all you are going to do is make stupid snyde comments, why not go here:

Admin Edit: foul language removed.

Wow! Maybe I'll go there someday. Heh heh.

Actually though, I'd be interested in a wattage meter that actually measures true power output from the rider. I'm not sure I'd like the one you're talking about. But the price sounds a lot better than those high priced ones. Maybe those can be had for no more than 1/2 retail on ebay. That would still be a lot of money. I have a feeling if I knew which product to buy, I'd figure out a way to get a good deal on it.

Those so called more accurate (or less approximate) meters I would be interested in understanding a little better. For example, how do they measure chain tension? How would they measure torque? Measuring acceleration is easy to see, but power for a given acceleration would seem to be higher for the cobblestones of Paris/Roubaix than smooth asphalt. I wonder if it factors that.

Also, it seems that very heavy winds don't get cancelled out. If you could see what you are generating truly in watts, it would probably be more motivating if you see that you are generating say 300 watts when your speedometer reads 12 miles an hour rather than say 100 watts with a meter that ignores the wind. I'm not a particularly strong rider. I'm I guess a fast recreational rider but not one to go to organized races. I ride a lot of miles--about 60 to 100 plus a day.

WINGNUTT, thanks for the clarification on the HAC4 not using cadence (I know my old CM414 didn't, but not sure about the HAC4).

gntlmn, the SRM power meters can be had for about $1200 or so now--they have two models and can often be found on ebay. I would suggest looking into the Polar HRM/Power output unit. This unit costs about $700 new for the whole thing (HRM plus power sensor kit). I'm not positive on how the chain tension is measured, but I know there is a sensor that mounts on the chainstay below the chain and this contributes to the power readings. I have heard pretty good things about this one, and at only half the cost of the best out there, it may be worth checking out. I believe this unit has more features than the HAC4 as well. You may want to try a google search for "Polar Power Meter" or "Polar Power Output Kit". This can be found at most online bike shops as well as on ebay.

Jeff