Average watts

[esoxlucius]

This could be a very daft question but I'm going to ask it anyway. My understanding of watts isn't great, so here goes.

I don't have a power meter on any of my bikes, just a basic computer that gives me the basic info. I often wonder how many watts I'm putting out but obviously have no way of measuring it.

But I started thinking. If you have your distance travelled, duration of journey and average speed, which my cycling computer has, is there then a very broad brush type of calculation that can be done which gives you a roundabout figure of the average watts you were putting out during the ride?

 

[Pblakeney]

This could be a very daft question but I'm going to ask it anyway.

I don't have a power meter on any of my bikes, just a basic computer that gives me the basic info. I often wonder how many watts I'm putting out but obviously have no way of measuring it.

But I started thinking. If you have your distance travelled, duration of journey and average speed, which my cycling computer has, is there then a very broad brush type of calculation that can be done which gives you a roundabout figure of the average watts you were putting out during the ride?

Strava gives you a guesstimated figure which would appear to be reasonably close.
Not during a ride but if you use the same routes regularly then you’ll have a rough idea of how it feels.

 

[esoxlucius]

Strava gives you a guesstimated figure which would appear to be reasonably close.
Not during a ride but if you use the same routes regularly then you’ll have a rough idea of how it feels.

Even though everyone else might be, I'm not on Strava, lol. I'm a bit of a luddite what can I say, lol.

I was thinking more along the lines of a basic calculation I can do myself using the info my computer gives me.

 

[esoxlucius]

I always thought you needed a dedicated cycling computer to use Strava, and mines just basic.

However, I've just been advised off my son that I can download the Strava app on my phone. I take my phone with me on every ride so if Strava gives you a reasonably accurate figure on watts, then I think I have a way of getting the info I'm interested in.

Told you I was a luddite, lol.

 

[Punkawallah]

There is a body of thought that considers if you are able to wonder how many Watts you are putting out, you are obviously not putting enough effort in :-)

 

[esoxlucius]

There is a body of thought that considers if you are able to wonder how many Watts you are putting out, you are obviously not putting enough effort in :-)

Lol. That could well be the case. But if you saw me after a ride, collapsing on the floor in a pool of sweat, it's undeniable that I'm putting plenty of effort in, lol.

 

[Pblakeney]

I always thought you needed a dedicated cycling computer to use Strava, and mines just basic.

However, I've just been advised off my son that I can download the Strava app on my phone. I take my phone with me on every ride so if Strava gives you a reasonably accurate figure on watts, then I think I have a way of getting the info I'm interested in.

Told you I was a luddite, lol.

The free version of Strava is perfectly adequate.

 

[Hacienda71]

To be honest having ridden with and without a power meter on Strava the estimate it gives can be way out. The same applies to a simple calculation as there are far too many variables such as weight, elevation, wind speed, road surface, position on the bike etc. to try to work anything meaningful. On the paid version of Strava you can compare your effort with others on the same day with a power meter, but even then they could be in a group ride or weigh a significantly different amount to you.
The next best fitness training metric to power is HR, but that is unique to you so doesn't give you a direct comparison to other riders. It does give you a repeatable metric for say intervals and also give you a bit of an idea of your fatigue levels.

 

[ColinJ]

Bike Calculator has a good go at it.

You will see a security warning because the site does not support https but you are only putting in speed, distance etc, not your bank details, home address, whatever, so don't worry about it!

I found the numbers it comes up with are pretty close to what my power meter tells me.

 

[Dogtrousers]

It's basically the same question as "is there a calculator to work out how many calories I burnt on a ride?" It's a very similar problem.

There are various tools that do this kind of thing and they give you a number that you can compare ride to ride so they are useful for monitoring your change over time, comparing one of your rides with another. But what they are not much good for is knowing what the real absolute value of your power in watts, or energy use in kJ or kCal is. They do their best with the data they have, and make loads of assumptions. Just don't compare the results with data obtained from another source.

In the past I've compared Strava estimates with PM data and it's generally not great at getting anywhere close to the absolute PM value. But tbh, I don't use Strava much so I have no idea what basic parameters for weight etc I have in there - and these will be crucial for the algorithm to have a chance. I wasn't scientific or systematic about my comparison.

 

[Dogtrousers]

Bike Calculator has a good go at it.

You will see a security warning because the site does not support https but you are only putting in speed, distance etc, not your bank details, home address, whatever, so don't worry about it!

I found the numbers it comes up with are pretty close to what my power meter tells me.

I've played with Bike Calculator in the past, putting in data for specific climbs and comparing it with my own power data and I've also found it returns results that correlate pretty well (within +/- <10% or so IIRC) with PM data.

But it doesn't really do what the OP wants, which is average power over an entire ride, not a single segment of a ride with consistent gradient.

 

[wafter]

If you're travelling at any sort of reasonable speed aero drag is where most of your energy is going, and this is incredibly difficult to model / account for accurately... so the easiest and most accurate way of quantifying power output is to use a power meter.

Failing that as already posted Strava and various propriatory bits of software associated with bike speedos / head units will give you power values, but these are only rough estimates based on generalised models of all the factors involved such as drag, rolling resistance etc.

If your rides are consistant (same equipment etc) these power figures probably have some value for comparison to each other, but have limited relevance otherwise and fail to take into account the effect of wind or downhill gradients (coast at 40mph down a big hill and Strava will tell you your power output is huge, when of course you're putting in zero effort).

While it's difficult to generally assess your power output throughout a ride, you can perform tests to get a decent idea of what you're capable of if you have a hill of known gradient and you know your all-up weight. Assuming you're travelling sufficiently slowly (so the steeper the better as long as it's manageable and you can maintain a cadence that's representative of typical riding), and wind is negligeable the aero drag becomes a marginal factor, meaning all your energy is going into elevating you up the hill.

I won't go into the derivation but it's all pretty simple maths to work out your energy output for your ascent from the hill's grad and your mass, then your power output by factoring in your ascent rate.

 

[si_c]

In the past I've compared Strava estimates with PM data and it's generally not great at getting anywhere close to the absolute PM value. But tbh, I don't use Strava much so I have no idea what basic parameters for weight etc I have in there - and these will be crucial for the algorithm to have a chance. I wasn't scientific or systematic about my comparison.

This has been my experience, there are many factors which Strava cannot take into account which just renders the figure they give meaningless.

Strava gives you a guesstimated figure which would appear to be reasonably close.
Not during a ride but if you use the same routes regularly then you’ll have a rough idea of how it feels.

Not even particularly useful for regular rides to be honest, a windy day followed by a calm day then another with wind blowing in a different direction, or a cold day then a hot day, will all result in different results and you won't know if you were just feeling better or not.

Using ride feel or heart rate are both much better ways of assessing output than an estimated power figure.

Fundamentally if you want a power figure, you need a power meter.

 

[N0bodyOfTheGoat]

For the Strava estimated power, wind assistance/hinderance isn't accounted for well iirc, but give it the best weight data you can (you; kit you're wearing on ride; bits in jersey pockets; bike; any extras fitted to bike; the bidons etc).

 

[ColinJ]

I've played with Bike Calculator in the past, putting in data for specific climbs and comparing it with my own power data and I've also found it returns results that correlate pretty well (within +/- <10% or so IIRC) with PM data.

But it doesn't really do what the OP wants, which is average power over an entire ride, not a single segment of a ride with consistent gradient.

I confess that my tests were done only on the Cragg Vale climb, which takes me over 25 minutes. That is long enough to get a good idea of what I could do on a longer, more varied ride. The calculator suggested that I had done 221 W. My power meter measured 215 W. Those figures are pretty close!

If no long hills are available then a flattish route taking 20+ minutes without stops for junctions etc. would give some useful data.

If there is a strong, gusty wind (like here today!) then any estimate is going to be more of a guesstimate!