Why are power meters limited to 2000 watts ?
 

Why are so many Power Meters limited to 2000w?

No need for people exploding and shouting "Only 1% of the human population can reach above 2000w so whats the point I hate you! this is a useless thread AARRGGG!:mad:"

All power meter manufactures claim that accuracy increases with higher wattage output, so why the limit?

Is a SRM Science and Infocrank the only +2000w Road option?

Can a Garmin Vector read 2000w per pedal and thus actually capable of reading up to 4000w?

Much much less than 1% I would guess.

When you can generate an average of 190 watts (.25 horsepower) you can fly across the English Channel in a human-powered aircraft like professional cyclist Bryan Allen did in 1979

^^That was a pretty neat video.

Interesting comparison:Great performances all but, giving Allen his due, wiki notes that the winged Albatross required 300W in calm air. Also, climbing to an altitude to get over the turbulence may have had him peaking at over 500. Moreover, there apparently was a hydration issue...

I doubt 1% of the human population have power meters.

So, the companies have to be catering to the elite among the elite cyclists. Are the "pros" able to peg the meters, even for a few seconds? It probably wouldn't make much difference for a training ride, but perhaps for sprint training.

I do wonder what the actual limitations of the power meters are. They have to have some kind of a force based strain gauge. If one is measuring the power at the rear wheel, then perhaps it all evens out. But if it is being measured at the pedals and crank arms, then the mashers, clydes, and weight lifters likely can generate significantly more force than the spinners. So, I would wonder if the limitation would actually be a software limitation, and not a hardware limitation.

Watts, not kilowatts.

But, yes, there is a huge difference between a 2 minute effort and a nearly 3 hour effort. Also the reason why 1 minute flat Strava segments are much faster than 30 minute segments.

there probably is a good reason, for example you would break the parts involved. I have been working on a load cell for a different application. Greater range can make your measurements less accurate. I got my trainer up to 1500 watts for about a second. Then my bike fell off the trainer.

it is indeed a interesting comparison but I think we can agree that a higher kWh doesn't necessarily mean a superior performance.


Bryan Allen, 2 hours 49 minutes at 190 kw = 0.535 kWh tofly across the English Channel in a human-powered aircraft

A.Z.K.( yes me :innocent: ), 4 hours 17 minutes at 245w = 1.049 kWh to do the RideLondon-Surrey 100 Sportive.

so I can push a greater kWh total than Bryan Allens channel cross but matching Robert Fostermanns 700w sustained toaster effort for a mere 108 seconds is slightly harder to achieve!

This is what i'm trying to understand myself. But after various questions in various forums I have had no proper response. Only people going on about how useless my question is and that i should spank myself for asking such a naughty question.

Power meters have cadence limits normally 30-200rpm they also have wattage limits mostly 2000w. but surely this is because there is actually a torque limit. but no one seems to know what these torque limits are.

interesting are load cells similar to strain gauges ?


From Verve Info Crank' Accuracy torque: ±0.2 Nm accuracy for measurements below 20 Nm, and ±1% of actual readings for measurements above 20 Nm '


So below 20Nm it becomes less accurate, at 5Nm it could be up to 4% out. SRM make the same claims of improved accuracy with higher output.

The power reading limitation doesn't limit your actual power, so you could break the parts irrespective of the meter being able to read it. Of course there might be a physical stop to prevent overloading the load cell. That won't limit your power, but it will limit the reading and prevent damage to the load cell or strain gauge. (load cell: strain member with associated strain gauge)

more about power. in this case power is torque*speed. Torque sensors (aka torque load cells) almost always use strain gauges, which measures the stretching of a structural part. This translates into a force, which can be used to calculate torque. There are also piezo sensors that would work, but that's a lot more money. Back to torque* speed. When my trainer locked up on me, the speed went to a very low level. Since I was in a mode where it wanted to control power, that meant the resistance went way up. So there is a trade off between torque and speed. If they have limitations on max torque, and min and max speed, that leads directly to a limitation on power.

Once you pick a range, then there are other things that determine accuracy. But with a strain gauge system, if you pick a huge range, as a practical matter you are left with fewer volts per watt to measure with. After all, there are very few cyclists that aren't weight weenies to some degree or another.

I think that people react strongly to this question because it's presented as a joke. Plus, very, very few cyclists ever put out a kilowatt, much less 2. Strava would know the approximate percentage of such monsters. When I was highly trained, many moons ago, I tried to put out a horsepower. In those long-gone days, we didn't have power meters, so I ran up some steps. I think I did manage to get fairly close to a horsepower, which is about 3/4 KW. Pretty sure I could put out a kW on a bike, but I've never bothered to get a power meter

Thank you for this constructive criticism. I look forward to more like it. I'm quite big for a cyclist and have hit the limiter on my Stages power meter multiple times, I have managed to do over 2000w on my Dual Vectors and am now wondering if its a glitch or that it can allow 2000w per pedal? hence my curiosity into the inner workings of a power meter.

With that being said it was still below 20w/kg. Shane Perkins puts out 2500w at around 90kg which is an astronomical 27.7w/kg!

https://www.youtube.com/watch?v=h8H6fU9VNgQ

now let me go look into this 'piezo sensors' !

>2000W probably is more academic than realistic if its milliseconds of peak power output --e.g.,

Nice way to wake up and make breakfast at teh same time in the morning...

If you were really thinking about making your own, the way to go is probably crank-based. Stages could probably re-range their meter, but I doubt they would want to do that for a one-off. Seems like there are some that use the deflection of the tube between the crank arms to measure torque, of course that's one sided. You could mount strain gauges on crank arms like stages does, but that is getting into significant development issues.

Piezo load cells have the advantage that no motion is required to measure a force. However, in this application I am not sure where you would put them, and the crank arms are being bent anyway, so there is no issue in measuring strains.

As far as your garmin pedals go, I suppose that if each pedal can measure 1kw, then 2 can measure 2kw. In practice, we usually don't put out significant power in both legs at the same time.

A baked potato could kill you.

I'm not seeing specs on all the power meters.

However, here are a couple:
Precision 4iiii
10 to 170 rpm
4000 Watts

Verve Infocrank
10 to 200 rpm
3000 Watts

I suppose it could be a problem for elephant trikes.

http://i.ytimg.com/vi/4cuDE1NrNNs/hqdefault.jpg

For how long were you hitting 2000 w?

If you are talking instantaneous (a second or two) power, then you are basically measuring your ability to leg press. You're weightlifting. So, use the gym to measure your "power" output over a couple seconds.

Yes its only for a few seconds. The power meter flat lines at 2000w so I don't know how much more it is.

Also since the power meter cant record over 2000w my 5 sec average (sprint power) is inaccurate.

I understand this sort of data is not really useful to most but I like to sprint, so seeing if i'm improving or not matters to me. And at the end of the day when i'm spending +£500 for a sensor on a bike I want it to be able to read all my wattage abilities.

2000w could be past the point of diminishing returns for utility/cost. If you want a tiny bit more accuracy, you may have to pay a lot more. And you might be willing, but the rest of the market might not be.

The Precision 4iiii (kit) I linked above is among the cheapest of the power meters and is rated for 4000W.

I was reading about cadence, and was surprising that some of the meters have troubles above 170 RPM or so, although it isn't always a fixed cutoff.

I wouldn't be surprised if overall system accuracy plummets above 2000W. However, the most important part would be reproducibility.

Sprints, of course, are of vital importance to racing. So, while a rider might only be hitting 2000W for a few seconds on a ride, those might be the most important few seconds for the whole ride/race. How many professional level sprinters, or climbers peg their meters? If they all do, then I would expect some changes.

Suppose everyone can do 3,500w.

How long can you hold it for?

Sure, it's great to jump on the pedals and feel the bike start to go, but then what? Are you going to win the race with your 1/4 second sprint?