Power to weight ratio

Billywiz

I've been cycling for several months now and saw some modest speed improvement when tackling hills. However the biggest boost in preformance only began when I started dieting and shedding a lot of weight. I would be interested if any one knows how to calculate power to weight ratio with out the expense of buying a power crank. I read an article on a top climbing cyclist who had power to weight ratio of 7 watts per kilogram but no mention of how this was calculated.

Thanks

Great site btw

Garybee

The only way of finding out your power output is to buy some kind of powermeter, or to get a test carried out with a coach on something like a kingcycle.

When you've done that you need to think about which power figure you want to know. For example, your Maximum Aerobic Power would be different to your Functional Threshold Power (power you can sustain for ~1hr).

Realistically though, unless you are going to do something with this information (build a training plan around it) there is no real use in knowing it. Sorry if this sounds dismissive, it's just that it really is just an abstract figure. If you found out you could produce 8W/Kg would it make you any faster?

cycologist

Well Billywizz, if this is the sort of question you are asking as a beginner - what on earth will you want to know as a more seasoned cyclist ? For the moment i would stick with your idea that if you shed a few pounds then the hills will be a bit easier and your speed will be a bit faster. Not very scientific but effective.

bahzob

Ditto above. I started cycling in order to shed some pounds. Caught the bug and got a power meter now but only because I am pretty much at a sensible target weight and aiming at events where power/weight has a big effect.

Suggest focus on continuing to build basic fitness/lose weight first. That said if you still want to know power/weight one thing you could do (and its not bad training) is find a good, longish, hill and time yourself from bottom to top. Hopefully you will get better and if you do it will be, in part because your power/weight ratio is getting better.

Once you have done this a few times and have some results, the article here gives a rough and ready calculation for your power on the climb:
http://www2.trainingbible.com/joesblog/2008/01/climbing-power-formula.html

Note: this will only give a very rough estimate so use with that advice and for fun only.

Billywiz

Thanks for the replies, bahzobs link is just the sort of area I'm interested in 8)

Dr Lim's formula:

bike + rider weight (kg) x 9.8 x elevation gain (meters) / time (seconds) = power (watts). Add 10% for rolling and air resistance.

Would it then be correct to simply divide watts by rider weight and thus get watts per kilogram? Any maths boffins out there?

azzerb

Yes that's right.

But make sure to take the 10% with a pinch of salt, and not too sure about part of the formula, but it's only for comparison reasons.

nasahapley

This is exactly the formula I've used for ages to calculate a rough power figure. I don't know how Dr Lim managed to get his name attached to it - it's just mgh/t, or potential energy gained divided by time - GCSE physics stuff! The only bit that might be inaccurate in the formula is the adding of 10%; if you don't add it (i.e. just calculate mgh/t), then you know that your power definitely cannot be below that figure, provided there's no tailwind. However, 10% does seem a reasonable amount to add on for transmission loss/drag etc.

kmahony

I use this site. You need to know avg gradient and speed for a climb.
http://www.kreuzotter.de/english/espeed.htm

azzerb

kmahony wrote:

I use this site. You need to know avg gradient and speed for a climb.
http://www.kreuzotter.de/english/espeed.htm

Ah thanks for reminding me, i knew something didn't feel right.

Not very good with Mechanics, my strength lies in pure. But you're right, you need to know the average gradient (so not just the vertical component as given in the formula, but also the horizontal, which you could get the gradient from)

But it's all approximations for comparisons over time, want proper values, just get a real powermeter lol.