Author Topic: Calculate Power  (Read 782 times)

Calculate Power
« on: April 13, 2020, 10:56:23 pm »
For no real reason, other than interest, I would like to know if it is possible to calculate power. I was sitting on my turbo earlier thinking about this. I can measure heart rate, cadence and speed (this is purely a turbo training exercise). So by using those measurements in some way, can I determine my power output?

vorsprung

  • Opposites Attract
    • Audaxing
Re: Calculate Power
« Reply #1 on: April 13, 2020, 10:58:51 pm »
do you have a fluid based trainer?

if so there is a direct relationship between the "speed" and the power you put in

you can probably look up a speed to power table and use it for power based training plans
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TimC

  • Old blerk sometimes onabike.
Re: Calculate Power
« Reply #2 on: April 13, 2020, 10:59:17 pm »
Bob, if you use Zwift, it has an algorithm that calculates your power output while on the turbo. It's not accurate compared to a proper power meter, or a calibrated smart turbo, but it's not that far off. You have to enter a few details, but it's not too difficult.

Re: Calculate Power
« Reply #3 on: April 13, 2020, 11:07:57 pm »
I do have a fluid based trainer, an Elite Crono. I'll head over to the Elite site and see if they publish a table.

I don't use Zwift and I don't want to buy a power meter. This was simply a thought whilst doing a turbo session this afternoon.

TimC

  • Old blerk sometimes onabike.
Re: Calculate Power
« Reply #4 on: April 13, 2020, 11:18:47 pm »
Bob, the point about using Zwift is that you don't need a power meter (unless you wish to race). The algorithm calculates your power from the very data you said have. However, I totally understand if Zwift doesn't interest you. I'm sure there are alternative sources of the same calculation!

Re: Calculate Power
« Reply #5 on: April 13, 2020, 11:43:36 pm »
No, Zwift does interest me but I don't subscribe at the moment. It maybe something that I look at. Need to work on my setup, screens etc, but it is possible.

fuaran

  • rothair gasta
Re: Calculate Power
« Reply #6 on: April 13, 2020, 11:45:57 pm »
Golden Cheetah can calculate virtual power. Seems it has support for some Elite trainers built in. It is free.

TheLurker

  • Goes well with magnolia.
Re: Calculate Power
« Reply #7 on: April 14, 2020, 06:32:09 am »
For a bit of a laugh you could....

Find steep hill of known height.
Time, seconds, how long it takes to ride up it from a rolling start

Pt = E  = mgh  mass in kg, g acceleration due to gravity 9.81 ms^2, h  vertical ascent in metres, t in seconds
 
P = E/t

If the hill is steep enough you'll be going slow enough that wind resistance won't be a significant factor and mass is you + the bike plus any pies in your saddle bags. :)
Τα πιο όμορφα ταξίδια γίνονται με τις δικές μας δυνάμεις - Φίλοι του Ποδήλατου

Pedal Castro

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Re: Calculate Power
« Reply #8 on: April 14, 2020, 06:33:24 am »
Before I got a smart turbo I used an Elite Chrono fluid trainer with speed and cadence sensor. TrainerRoad calculated virtual power which was pretty much the same as the power meter I have now on my Direto and power tap hubs. For TrainerRoad it uses a different power curve for each trainer so as long as your trainer is in the supported list you're good to go. I assume Zwift works the same way but not sure.

Pedal Castro

  • so talented I can run with scissors - ouch!
    • Two beers or not two beers...
Re: Calculate Power
« Reply #9 on: April 14, 2020, 06:37:47 am »
For a bit of a laugh you could....

Find steep hill of known height.
Time, seconds, how long it takes to ride up it from a rolling start

Pt = E  = mgh  mass in kg, g acceleration due to gravity 9.81 ms^2, h  vertical ascent in metres, t in seconds
 
P = E/t

If the hill is steep enough you'll be going slow enough that wind resistance won't be a significant factor and mass is you + the bike plus any pies in your saddle bags. :)

My year 9 class would be running up the physics building stairs every year when we covered power=work done/time taken.  ;D

LMT

Re: Calculate Power
« Reply #10 on: April 14, 2020, 07:15:13 am »
Find a hill where you know the average grad and the elevation, time your climb and then using VAM you can find your w/kg and then from that your power.

Re: Calculate Power
« Reply #11 on: April 14, 2020, 08:43:00 am »
In different times it might be easy to find a local gym with a Wattbike; there are two or three options for testing on it, and it’s the most accurate.

A good indicator of effort is pulse rate. If you get establish a maximum ( hard as you can up a hill for example), there are tables on British Cycling and the Wattbike web site that will show you your pulse rate for levels 1 to 5.

Re: Calculate Power
« Reply #12 on: April 14, 2020, 09:12:34 am »
The only way you will get a half decent estimate with that trainer is using a program that can read wheel speed and perform some roll down tests. The power curves published by the manufacturer are all very well, but the resistance of a wheel on trainer is significantly affected by the tyre pressure (and roller position).

Trainer Road say that their "Virtual Power" should be consistent (assuming you keep the tension and the tyre pressure the same), but will not be precise. I found that my FTP was over 20W different when using power measuring pedals as opposed to the Virtual Power number (for the same test). So it's a useful number for setting training zones, but it's not comparable to anyone else - that's probably the opposite of what you want!

TimC

  • Old blerk sometimes onabike.
Re: Calculate Power
« Reply #13 on: April 14, 2020, 12:15:52 pm »
Find a hill where you know the average grad and the elevation, time your climb and then using VAM you can find your w/kg and then from that your power.

On a turbo? Can you make a demo video for us?!

fuaran

  • rothair gasta
Re: Calculate Power
« Reply #14 on: April 14, 2020, 12:41:36 pm »
Also things like the PowerCal. It is just a heart rate monitor strap, but it calculates power from that, and transmits it. So it can appear as a 'power meter' for other devices. Seems it is fairly accurate for most people.
https://www.dcrainmaker.com/2012/11/cycleops-powercal-in-depth-review.html

Though that is quite old now, don't know if there is any newer better version. Presumably it could all be done with a regular heart rate monitor, plus software to calculate virtual power. If you could figure out an algorithm? Think it is based on rate of change of heart rate, not just the current number.

LMT

Re: Calculate Power
« Reply #15 on: April 14, 2020, 01:24:56 pm »
Find a hill where you know the average grad and the elevation, time your climb and then using VAM you can find your w/kg and then from that your power.

On a turbo? Can you make a demo video for us?!

A demo video? Sure, pay us a couple of grand and it's done - I'll PM you my bank details to make the transfer?


TimC

  • Old blerk sometimes onabike.
Re: Calculate Power
« Reply #16 on: April 14, 2020, 02:13:37 pm »
Find a hill where you know the average grad and the elevation, time your climb and then using VAM you can find your w/kg and then from that your power.

On a turbo? Can you make a demo video for us?!

A demo video? Sure, pay us a couple of grand and it's done - I'll PM you my bank details to make the transfer?

 ;D

Re: Calculate Power
« Reply #17 on: May 03, 2020, 07:59:45 pm »
If you have a load cell attached to your cranks, multiply the figures from that by your cadence ( multiply  how many times you can rotate the cranks in 15 seconds by 4). That’s your average power. Its far easier to just get power meters though. You can then get all sorts of lovely numbers, and graphs, and stuff that you can use to judge how your performance is coming along.
Loving life with a beautiful Bianchi.

Re: Calculate Power
« Reply #18 on: May 06, 2020, 05:57:44 pm »
Golden Cheetah can calculate virtual power. Seems it has support for some Elite trainers built in. It is free.

It is a programmer’s delight;)