[Closed] Cheap power meter?

I've done about 3 rides in 2 months, beyond my 5 mile commute. Last year I did a 226 with 6:10 or so for the bike leg, so my result (which appears to out me in near world class territory) is patently wrong.

nj it's maybe 0.7 of a mile.

height gain is 115m (from a mapmyrun, could be inaccurate), me + bike = 90kg, time is 3:20.

So is it only the vertical component that matters?

I only ask as I tried to calculate it as a comparison.

There's a small climb near me, 18m gained in 1.12km, all uphill. My fastest (measured) time is 364w, 1 minute 50, so how does the calc work? I'm 67kg, so call it 74kg for me + bike.

If the calc is:

(mass (74kg) * height (18m) * 9.8 )/ 110 seconds = 118W

If it's the distance covered:

(mass*distance (1120m)*9.8)/110 seconds = 7383W

Neither of which are right. I imagine my calcs are well off, just genuinely curious to see how far off it is.

Edit: taking something with a little more elevation: 134m in 2097m in 402 seconds gives 241w, versus a measured 317w, so still way out.

Roughly working out in my head so could be fairly well out:

Total power =
power needed to overcome rolling resistance +
power needed to overcome aerodynamic resistance +
power needed to overcome changes in speed (kinetic energy) +
power needed to overcome changes in elevation (potential energy).

The first three are arguably negligible when climbing at low speeds. The rough equation for the final one would be:

Power = slope (%) * speed (m/s) * total mass (kg) * 9.8 (m/s^2).

I think this should work!

Power = slope (%) * speed (m/s) * total mass (kg) * 9.8 (m/s^2).

Using my second example:

7% * 5.052m/s * 74kg * 9.8m/s^2 = 256w, so still seems low to me.

I think wind resistance is a relevant factor at that speed.

Yes I think you need something very steep and slow to negate that.

I think wind resistance is a relevant factor at that speed.

It's only just over 11mph?

Is 564W for a 80kg male realistic?

In a word. No.
If you are looking for something as a comparison, then VAM and a long hill is better than guessing at power.

When I first got my power meter I compared a few climbs between estimated and actual on Strava for the sameish times, it's not that far out on the steeper stuff. I think it was something like 7-8% climbs that seemed to line up the best.

564W would make you a shit hot cyclist, and very few people would be able to beat that. You'd be mixing with the best in your area I reckon.

For a cheap power meter, your best bet is to go on ebay and look for them - most likely get an old wired Powertap hub for a couple of hundred.

P = mass x height gain x g / time

Gravitational potential energy is mass x g x height difference, and divide this by the time it takes to get up there.

A bit of googling suggests the mapmyride gps height info is 35% odd overstated.

Looks like I won't be winning the tour after all.

366W and 4.5W/kg are Shirley unrealistic tho.

Why do you think it is unrealistic?

Actually it pegs me as a 4th cat equivalent which sounds about right on a good day.

I would take those tables with various categories and power values with a massive pinch of salt, although it tends to be the longer power values that are least accurate, especially FTP.

366W and 4.5W/kg are Shirley unrealistic tho.

I reckon that would put you in the running to win at Sport category MTB races.

I'm no sandbagger!

I got a couple of podiums at masters in my day.

I keep thinking I should give it a go again, but I'm too lazy/unmotivated.

Note that as a relative chubster, your power value would have to be quite high to be competitive. W/kg might be more relevant. There's a reason most cyclists are skinny midgets. (Flat time trials are perhaps a bit of an exception, but even then a larger person will have more air resistance.)

"Relative chubster" ❓

How very dare you etc.

Sorry 😆 of course 80kg doesn't make you fat. But it does take more watts to push uphill than 65kg at the same speed

I reckon that would put you in the running to win at Sport category MTB races.

If it were FTP then maybe. 3 minute output? No chance!

Agreed. Last time I checked my 5 minute power was about 5.6 w/kg, and I'm certainly not winning sport races!

Oh yeah forgot it was only 3 mins 🙂

I think power outputs is the new bike weights thread.
Some people are seriously over-rating their power outputs.

366w FTP, depending on rider weight would be at the sharp end of Elite.

http://www.strava.com/segments/arthur-s-seat-climb-686793

The strava segment. 3.20 would put you in between Jar and Walter - walter placing top 10 in cat 3/4 races, Jar wins hill climbs for comparison. Both train with 9.30s.

Thanks Claire - my route is a little shorter tho.

What does training with 9.30s mean?

When I first got my power meter I compared a few climbs between estimated and actual on Strava for the sameish times, it's not that far out on the steeper stuff. I think it was something like 7-8% climbs that seemed to line up the best.

Thats the thing really, how accurate do you really need it to be, given Strava does its estimates based on the data you input and your logged performance, they've probably used the data uploaded by people with power meters to refine the calculation further...

Coming back to the OPs original questions:

Does any such thing (cheap power meter) exist?

Not that I know of...

Or is there an online resource that allows one to estimate it from say height & speed?

Yep, Strava...

Or is there an online resource that allows one to estimate it from say height & speed?
Yep, Strava...

I meant without gps and rider height not elevation.

[url= http://bikecalculator.com/ ]How about this? [/url]

[url= http://www.kreuzotter.de/english/espeed.htm ]Or this?[/url]

What does training with 9.30s mean?

OP, depending on what you want it for, the powercal might suffice. Uses rate of change in your HR to guesstimate power, and works better than it has a right to. You don't get real time data though.
[url= http://www.dcrainmaker.com/2012/11/cycleops-powercal-in-depth-review.html ]powercal [/url]

Or if you don't need power analysis on the road, you can hook up your turbo to the computer with an ANT+ USB stick and get estimated power using a program like GoldenCheetah. Doesn't give you, say, an ftp you can use in comparison to other riders but to track your own progress it's useful.

I'm wrong about powercal, seems it does give real-time power.

Ta C - is that much faster than Tuesday nights?

Bob - thanks, looks interesting.

Tired off here has a powercal, some more info on the last page of my thread here: http://singletrackworld.com/forum/topic/which-power-meter-stages-or-power2max/page/3

What about a 2nd hand powertap? You could probably pick one of the wired ones up for 150 notes. I've got one I want to offload, but I'm not in the country.

Re: 564 for 3 mins, I'd of thought any half decent roadie would get somewhere near those numbers on a good day, probably put you at about cat 2 if you are 80kg. If you are under 70kg you'd be riding near elite level, well were I live anyway.

Double post whammy.

If you'd like to see powercal data, [url= http://www.strava.com/activities/162635458/analysis ]here[/url] is yesterday evening's ride around Swinley. It was fairly gentle ride with Teen1, and the average power reflects this. The peak power is likely to be off, but rather pleasingly, power drops when I stop riding much faster than heart rate. Couple of nice sharp steep climbs on my Single speed show in HR and power.

I'd never seen one of those before - interesting. I never thought that anything without a torque tube would provide accurate numbers. How does it account for heart rate effected by what you've eaten, how hot it is etc? Heart rate is such a lagging factor I can't see how the short term numbers can be accurate?