How to work out watts/kg ?

aw1808

Hello ,

Bit of a stupid one and hopefully its an easy calculation . I know how much myself and my kit weighs and i know how long it took me to climb Alpe D'Huez . Is there an easy way to work out what my average power in watts and my watts per KG were for the climb ?

aberdeen_lune

We're you using a power meter on the climb? If yes divide the watts by your weight in KGs. If no then your stuffed.

napoleond

You need to have used a power meter or it's impossible. Any estimates will be subject to huge variation therefore useless.

marcusjb

Upload your ride to Strava, it will analyse the climb using their highly evolved algorithms taking almost none of the factors that can influence the result into account and come up with a figure that is complete and utter fiction.

paul2718

You can make an estimate, but it's not necessarily meaningful.

So, if you have an all up mass of 90kg, and climb the 1100m of Alpe d'Huez in an hour,

Total work = 90*9.8*1100 = 970200J

So average power = 970200/3600 = 269W

Which is a plausible number. If you go to a relevant Strava segment leader board and look at the recorded power for riders recording about an hour the numbers come out about right. Change the mass, elevation and time according to where you stopped at the top, how long you took and what you and your bike weigh. Do not wager anything you care about on the result.

Paul

term1te

You could try to calculate it from your VAM as defined by he who must not be named.

http://en.wikipedia.org/wiki/VAM_(bicycling)

Of course it won't be as accurate as a powermeter, but will give you an idea.

I'm off up the Alpe next week, what was your time?

Alex_Simmons/RST

aw1808 wrote:

Hello ,

Bit of a stupid one and hopefully its an easy calculation . I know how much myself and my kit weighs and i know how long it took me to climb Alpe D'Huez . Is there an easy way to work out what my average power in watts and my watts per KG were for the climb ?

If you use the same measurement points as TdF, then this will give you are reasonable estimate:

http://alex-cycle.blogspot.com.au/2011/ ... rtals.html

Of course any average wind vector will impact with the number somewhat:
http://alex-cycle.blogspot.com.au/2013/07/windbags.html

davidof

Alex_Simmons/RST wrote:

Of course any average wind vector will impact with the number somewhat:
http://alex-cycle.blogspot.com.au/2013/07/windbags.html

.

You can add 0.05% for drive train losses and road friction (the road is pretty smooth). The wind component won't be more than a few % unless it was blowing a gale or the rider was Marco Pantani.

aw1808

Thank you , i have a rough idea what watts and its not impresive in terms for what you guys would climb it in.

I managed 1 hr 27 which i am happy about and im a 90kg rider which im pleased about and gives me somehing to focus on for my next trip .

maryka

This is the best simple site I've found for estimating watts for "pure" climbs (i.e., solo, not drafting anyone, not much variable head or tailwind) if you can make good guesstimates at the other factors. It works both ways too, if you know your real watts you can estimate how long it will take you to do any definable climb.
http://bikecalculator.com/wattsMetric.html and http://bikecalculator.com/veloMetric.html

So 1h27 at 90kg up Alpe D'Huez is about 235w.

If you want to get more complicated, try http://www.kreuzotter.de/english/espeed.htm

Alex_Simmons/RST

davidof wrote:

Alex_Simmons/RST wrote:

Of course any average wind vector will impact with the number somewhat:
http://alex-cycle.blogspot.com.au/2013/07/windbags.html

.

You can add 0.05% for drive train losses and road friction (the road is pretty smooth). The wind component won't be more than a few % unless it was blowing a gale or the rider was Marco Pantani.

Hmmmm. Wind has a substantial impact on climb times, even very light barely noticeable wind.

Alex_Simmons/RST

davidof wrote:

Alex_Simmons/RST wrote:

Of course any average wind vector will impact with the number somewhat:
http://alex-cycle.blogspot.com.au/2013/07/windbags.html

.

You can add 0.05% for drive train losses and road friction (the road is pretty smooth). The wind component won't be more than a few % unless it was blowing a gale or the rider was Marco Pantani.

Drivetrain efficiency depends on where you measure power. On good road bike it's about 2-3% if power measured from cranks and all but zero if you are measuring at rear hub.

The calculation already includes rolling resistance, assumption on Crr is shown.

aw1808

I was curious more than anything and want to beat my own time up there next year which is why i wanted a guestimate . Obviously at 90kg im on the heavy side compared to normal riders and know that the key will be dropping weight and increasing power.

I have not dabbled with a power meter as i cant justify it as im just an avergae rider but i know what i need to do for my next trip !

bahzob

aw1808 wrote:

.... the key will be dropping weight and increasing power.

I'd advise prioritising one over the other. As a general rule if your BMI above normal then I'd suggest losing weight first by following a sustainable balanced calorie restricted diet, doing exercise in as well but not fretting about setting PBs and certainly not eating anything extra to "fuel" workouts.

Once you hit normal BMI range then, if you like, swap focus to improving power. By then you should have established good habits in terms of eating and will be able to make informed decisions about what diet changes are needed to be able to handle the extra workload.

onemoresolo

Alex_Simmons/RST wrote:

aw1808 wrote:

Hello ,

Bit of a stupid one and hopefully its an easy calculation . I know how much myself and my kit weighs and i know how long it took me to climb Alpe D'Huez . Is there an easy way to work out what my average power in watts and my watts per KG were for the climb ?

If you use the same measurement points as TdF, then this will give you are reasonable estimate:

http://alex-cycle.blogspot.com.au/2011/ ... rtals.html

Of course any average wind vector will impact with the number somewhat:
http://alex-cycle.blogspot.com.au/2013/07/windbags.html

I found that was a fairly decent way of estimating power, give or take 10W or so. It gives you an idea anyway.

aw1808

bahzob wrote:

aw1808 wrote:

.... the key will be dropping weight and increasing power.

I'd advise prioritising one over the other. As a general rule if your BMI above normal then I'd suggest losing weight first by following a sustainable balanced calorie restricted diet, doing exercise in as well but not fretting about setting PBs and certainly not eating anything extra to "fuel" workouts.

Once you hit normal BMI range then, if you like, swap focus to improving power. By then you should have established good habits in terms of eating and will be able to make informed decisions about what diet changes are needed to be able to handle the extra workload.

I have lost 8kg this year so far so i intend to just keep doing what i am and then look at my training properly when i reach the weight im happy with .