Any way to measure power output (watts) without powermeter?

brit66

For example, for those who have a power meter what sort of power do you need to exert to cycle at a speed of say 18mph, 22mph, 25mph or 30mph?

Assuming the road is flat with no wind and the bike is a typical mid-range road bike?

I know this is all pretty unscientific but am curious to know how I'd compare with a pro-rider like Cancellara?

...and yes, I know he would cain my arse!

Team Banana Spokesman

LOL

dennisn

brit66 wrote:

For example, for those who have a power meter what sort of power do you need to exert to cycle at a speed of say 18mph, 22mph, 25mph or 30mph?

Assuming the road is flat with no wind and the bike is a typical mid-range road bike?

I know this is all pretty unscientific but am curious to know how I'd compare with a pro-rider like Cancellara?

...and yes, I know he would cain my ars*!

If you rode your bike over a 40 KM flat route with no wind at 25 MPH, then did the same route again under the same conditions at 15 MPH it would take you longer but you would still use the same amount of energy. You would need to use more power during the 25MPH attempt and less during the 15MPH, but total power output for each one would be the same. I think. In any case I'm sure someone will be along soon to provide some sort of
formula's to calculate watts of power for you, given certain parameters. They possibly
will also tell me I've got my head up my *ss and they might be right, but I try.

Homer J

you would need 850W FC would only need 650W

KDub

I think the math relating speed to wind resistance is not linear, but exponential, so (all things being equal) it would take more energy to ride the same distance at a faster pace even though it took less time. However the whoopin' by Cancallara would be the same. :^)

DaveyL

It is very difficult to say as aerodynamics have a big effect on the flat - actually comparing times on a climb might be easier!

But check out analyticcycling.com and have a play about with the numbers there. You'll be able to see what sort of powers are required to move the same rider those speeds. It may not be 100% accurate but you will get some ballpark numbers - and be prepared to see power go up a bit more dramatically than speed!

dennisn

KDub wrote:

I think the math relating speed to wind resistance is not linear, but exponential, so (all things being equal) it would take more energy to ride the same distance at a faster pace even though it took less time. However the whoopin' by Cancallara would be the same. :^)

I was ignoring the aero factor. Just trying to say that to move any mass a given distance
requires the same total output no matter the speed(in a vacuum). I THINK?? Once again someone may need to come over and help me get my head out of my *ss.

I'm real sure you're right about the whoopin' though.

phil s

The only thing you need to know is that Cancellara would rip your lungs out through your arse

brit66

you would need 850W FC would only need 650.

Why would FC only need 650 - I don't understand?

check out analyticcycling.com and have a play about with the numbers there.

Thanks, I did and this is what I got:
At 22mph I'd need to output 395 watts and 494 watts for 25mph.

I know there are a huge number of variables at work here but I rowed for 12 years and therefore it's easy to compare the power (probably should say 'effort') you need to post a similar score to someone like Steve Redgrave because of the electronic read out on an ergometer.

I'm just trying to gauge just how much effort is required to try to match some like FC - even if only for 2-3 mins.

dennisn

brit66 wrote:

you would need 850W FC would only need 650.

Why would FC only need 650 - I don't understand?

check out analyticcycling.com and have a play about with the numbers there.

Thanks, I did and this is what I got:
At 22mph I'd need to output 395 watts and 494 watts for 25mph.

I can't verify the numbers but I do know that you must exert more watts of power if you want to increase your speed. If you can't hold 494 watts then you will start to slow down.

DaveyL

brit66 wrote:

you would need 850W FC would only need 650.

Why would FC only need 650 - I don't understand?

check out analyticcycling.com and have a play about with the numbers there.

Thanks, I did and this is what I got:
At 22mph I'd need to output 395 watts and 494 watts for 25mph.

I know there are a huge number of variables at work here but I rowed for 12 years and therefore it's easy to compare the power (probably should say 'effort') you need to post a similar score to someone like Steve Redgrave because of the electronic read out on an ergometer.

I'm just trying to gauge just how much effort is required to try to match some like FC - even if only for 2-3 mins.

That sounds like a fairly non-aero rider as the numbers are maybe a bit high, but it gives you an idea.

For info, he averaged ~280 Watts for the whole of the Tour of Flanders, and his max was 1450 Watts (presumably when he attacked on the Muur).

Bronzie

brit66 wrote:

At 22mph I'd need to output 395 watts and 494 watts for 25mph.

Sounds high - I can average around 22mph on my road bike @ 270W - I'm 74kg and 6'2", so not too aero either. Terrain, road surface, traffic conditons, wind direction and strength all have a massive influence though of course.

Insufficient data to comment on power required at 30mph

Homer J

I did a comparison test between my old microwave and my new one

grahamcp

brit66 wrote:

you would need 850W FC would only need 650.

I'm just trying to gauge just how much effort is required to try to match some like FC - even if only for 2-3 mins.

Are you over-complicating the question? Why not forget about power and just try to match the speed of Cancellara? In Flanders, Boonen was quoted as saying he was chasing FC at 55kmh (over 34mph) and still lost a minute. Average speed for the whole 262km race was around 40kmh(25mph). Of course he will have been drafting in a bunch for a large part of that, and we don't know much about wind speed/direction etc etc... but that push at the end was phenomenal (and P-Roubaix perhaps moreso).

Let us know how long you last at 34mph :twisted:

DaveyL

I think the course is pretty much slightly downhill from the top of the Muur to the finish, which might partly explain the high speeds during Boonen's doomed pursuit of Cancellara.

neeb

actually comparing times on a climb might be easier!

A lot easier actually, if you want to get a good approximation of your watts output at threshold. When you are climbing you are basically hauling the weight of yourself and your bike upwards against gravity. If you know how long it took a given rider of a given weight to ascend a reasonably steep climb and what his average wattage was, you should be able to calculate your watts fairly accurately by timing yourself over the same route and factoring in your weight. Eg. you need to put out about 4 watts per kilo to climb Alpe D'Huez in just under an hour.

brit66

Eg. you need to put out about 4 watts per kilo to climb Alpe D'Huez in just under an hour.

I weigh 77kg so I'd need to output 308 watts - interesting to know.

Why not forget about power and just try to match the speed of Cancellara? Average speed for the whole 262km race was around 40kmh(25mph).

Even an amateur race around an undulating course near where I live averages about 24mph. Drafting obviously helps maintain these high speeds but you alwas get those lone breakaways where the rider seems to be able to hold this speed for long periods (no doubt see this again in this years TdF). I try to imagine on a training run or commute me doing the same... I suppose that answers the question.... I simply cannot.

Cheers

neeb

I weigh 77kg so I'd need to output 308 watts - interesting to know.

That's as an average, over the space of the hour of course. Your sustainable watts over an hour will be a bit less than over, say, 20mins, and a lot less than over 5mins.

beatsystem

Go to this page and you can get all the info you need
http://bikecalculator.com/wattsUS.html

neeb

Wow, that just shows how much aerodynamics matters on the flat! I put in the speed I can normally manage when I'm zipping along uninterrupted, with "hoods" selected for the hand position. The wattage it came up with was way above my threshold! Then I changed it to "drops" and the watts number that came out was way below what I can manage...

How much does a session in a wind tunnel cost...?

Bhima

A climb will be affected by aerodynamics a lot too. Just less than the flat.

Looking at speed on indoor rollers will be more controlled. Still imperfect, but more consistent.

disgruntledgoat

Bhima wrote:

A climb will be affected by aerodynamics a lot too. Just less than the flat.

Looking at speed on indoor rollers will be more controlled. Still imperfect, but more consistent.

I don't think a climb is particularly effected by aerodynamics as the major force acting upon you is gravity not air resistance. The ratio between the two is obviously affected by the gradient of the slope, however.

Bhima

For a while, my benchmark test hill was a 3-3.5 minute effort but one day there was a tailwind and I did it in 2:35. Big difference.

My commute is all hills and can vary from 50 minutes to 70 minutes. Again, massive difference!

neeb

For a while, my benchmark test hill was a 3-3.5 minute effort but one day there was a tailwind and I did it in 2:35. Big difference.

My commute is all hills and can vary from 50 minutes to 70 minutes. Again, massive difference!

How steep were the hills? The steeper they are, the less air resistance matters. On the flat, there are huge differences due to air resistance even if there isn't a wind. Once you are climbing something over 6 or 7% for any extended period though, you would need a pretty stiff tailwind to make much difference. There aren't really any "proper" hills in the UK!

amaferanga

neeb wrote:

For a while, my benchmark test hill was a 3-3.5 minute effort but one day there was a tailwind and I did it in 2:35. Big difference.

My commute is all hills and can vary from 50 minutes to 70 minutes. Again, massive difference!

How steep were the hills? The steeper they are, the less air resistance matters. On the flat, there are huge differences due to air resistance even if there isn't a wind. Once you are climbing something over 6 or 7% for any extended period though, you would need a pretty stiff tailwind to make much difference. There aren't really any "proper" hills in the UK!

I can't see why you'd think that a 20mph wind, be it a head or tail wind, wouldn't make a fair difference even on a 7% climb. It does.

And you need to get out more if you think there are no proper hills in the UK

Bhima

I'm talking 10-20% climbs. Barely anything below 5% for any significant ammount of time.

West Peak District, near Macclesfield.

The difference between a headwind and tailwind can be two sprockets on the back for the same power output on a 10% climb for me.

Jeff Jones

I've found similar results for climbs around here. 7'15 (light tailwind) and 7'40 (light headwind) for the same climb @ exactly the same power on two different occasions.

It's not a shallow climb either, averaging 7.4% for 2.2km.

neeb

Wasn't saying that a headwind or tailwind doesn't make a difference - of course it does. But it needs to be moderately strong to have a big effect on a climb. If there is (subjectively) not much of a wind, then you can use your elapsed time and total weight (including bike) to calculate wattage pretty accurately on a long, steepish climb. You can't do this on the flat, because whether there is a wind or not, air resistance is a huge factor. On a climb it is only significant IF there is a decent wind...

Alex_Simmons/RST

Two 6% rides of 1 km. One with 2m/s tailwind, the other with 2m/s headwind.
21 seconds difference for this rider.

Distance 1,000 metres
Power 300.0 Watts
Temperature 20.0 C
Air Pressure (sea level) 1,010 hPa
Relative Humidity 50 %
Elevation 50 metres
Mass of bike + rider 80.00 kg
Gradient 6.00%
Wind Velocity (relative to Ground -ve = tailwind) -2.00 metres/second
Crr 0.0050
CdA 0.300 m^2
Speed 5.63 m/s
20.26 km/h
12.59 mph
Time 177.73 seconds
0:02:58 h:mm:ss


Distance 1,000 metres
Power 300.0 Watts
Temperature 20.0 C
Air Pressure (sea level) 1,010 hPa
Relative Humidity 50 %
Elevation 50 metres
Mass of bike + rider 80.00 kg
Gradient 6.00%
Wind Velocity (relative to Ground -ve = tailwind) 2.00 metres/second
Crr 0.0050
CdA 0.300 m^2
Speed 5.02 m/s
18.07 km/h
11.23 mph
Time 199.20 seconds
0:03:19 h:mm:ss

neeb

Oh well, I'm not going to argue with that, I guess I am underestimating the effect of air resistance when climbing. I'm surprised that 2m/s makes such a difference at 6% though.

But surely there must be a gradient at which 2m/s wouldn't really be significant? What would that be?

Alex_Simmons/RST

it reduces but is still there

Here's 10% gradient. 16 seconds difference. but over 4.5-5-minutes

Distance 1,000 metres
Power 300.0 Watts
Temperature 20.0 C
Air Pressure (sea level) 1,010 hPa
Relative Humidity 50 %
Elevation 50 metres
Mass of bike + rider 80.00 kg
Gradient 10.00%
Wind Velocity (relative to Ground -ve = tailwind) -2.00 metres/second
Crr 0.0050
CdA 0.300 m^2
Speed 3.64 m/s
13.09 km/h
8.14 mph
0:04:35 h:mm:ss


Distance 1,000 metres
Power 300.0 Watts
Temperature 20.0 C
Air Pressure (sea level) 1,010 hPa
Relative Humidity 50 %
Elevation 50 metres
Mass of bike + rider 80.00 kg
Gradient 10.00%
Wind Velocity (relative to Ground -ve = tailwind) 2.00 metres/second
Crr 0.0050
CdA 0.300 m^2
Speed 3.44 m/s
12.37 km/h
7.69 mph
0:04:51 h:mm:ss