Anyone know how weight affects the power:weight ratio?

[Panter]

Is it as simple as if a 100Kg rider looses 10% of his bodyweight, then on the same, long steady hill, they could expect to ascend 10% faster for the same affort?

Or is it (as I suspect) a lot more complex
Just a rough idea would be good, ignoring changes in drag, tyre friction etc........

 

[I am Spartacus]

NOT straightforward.
However, using FTP functional threshold power over a standard 1 hour TT.
Using a power meter... knowing the power used in that period.
eg 300 watts
divide it by rider weight in kg
80
pwr = 3.75
a good amateur is 5 and above

Now lose that 10kg.. will you be able to maintain that power?

 

[Fiona N]

I think you're (both) confusing things: power to weight ratio is the achieved (maximum, sustained, whatever) power output divided by the individual's mass in kg - i.e. 500 watts/75 kg. You need to define a bit more carefully what power measurement you're using as the instantaneous max output by a sprinter may be >1000w but it won't do him much good on a 250m long 25% hill. A better measure might by the last 3 minute interval achieved in a ramp test before failure or, for real endurance work, the power output on the anaerobic threshold.

But how this relates to the speed on the road or up a hill is the complicated bit, so that just because two individuals have the same p/w ratio doesn't mean that they'll be able to get up the hill at the same speed

 

[Panter]

Sorry, I should've made that a bit clearer.

Hil: 10 miles long with a gradient of 5%.

Cyclist: 100Kg plus bike who generates a constant 400W and climbs the hill in one hour.

If that cyclist then looses 10Kg in weight, but still mantains 400W for up to one Hour, how fast would he climb the hill?
(Not accounting for drag factor, tyre friction or anything else that would affect the result except for the pure reduction in mass.)

Basically , if a fat bar-steward (me) looses weight (fat,) what sort of very rough reduction could I expect to see in my commute time barring any sort of CV improvements ?

EDIT: Thanks for the comprehensive replies BTW, I didn't realise that power:weight was an actual measurement with applied parameters.

 

[I am Spartacus]

I think you're (both) confusing things: power to weight ratio is the achieved (maximum, sustained, whatever) power output divided by the individual's mass in kg - i.e. 500 watts/75 kg.

Nope , not confused here..
I did say sustained power... not absolute power for a burst.. that wont get you anywhere.
ok the standard is 1 hour, but if your pwr is good over 30 mins, then you be competitive.

PWR is DEPENDENT on TIME.. you cant just say a rider has pwr of 4.. it has to be over a period of time to make it relevant and relevant.

If you have a PWR higher than your 'opponent' then you will more likely make it to the top of the hill quicker, despite a bigger mass.
However, when the incline sharpens up over 10%, things tend to even out.

 

[Garz]

Sorry, I should've made that a bit clearer...

If that cyclist then looses 10Kg in weight, but still mantains 400W for up to one Hour, how fast would he climb the hill?

It is clear. Same power but less mass to move should mean that over the ten mile distance some time will get shaved off.

Now put this thread under the carpet or behind the door before jimbo sees it!

 

[Panter]

Nope , not confused here..
I did say sustained power... not absolute power for a burst.. that wont get you anywhere.
ok the standard is 1 hour, but if your pwr is good over 30 mins, then you be competitive.

PWR is DEPENDENT on TIME.. you cant just say a rider has pwr of 4.. it has to be over a period of time to make it relevant and relevant.

If you have a PWR higher than your 'opponent' then you will more likely make it to the top of the hill quicker, despite a bigger mass.
However, when the incline sharpens up over 10%, things tend to even out.

I see what you're saying, but I'm trying to strip it right back to basics. The rider in my question generates exactly 400w, from climbing on the bike, to collapse after 1Hr 30mins

It is clear. Same power but less mass to move should mean that over the ten mile distance some time will get shaved off.

Now put this thread under the carpet or behind the door before jimbo sees it!

That's the fella, but just how much time?

*and another sneaky thread bump*

 

[MacB]

I think Panter's looking for something a bit more simplified just as a way of making targets for himself. If it was laid out as a formula and he could mess about with the input value for weight to see how that impacted on time. I don't know the actual answer but something expressed along the lines of:

time = (power*mass)/distance

Find a run you like doing and record your time, weight and the distance. You can then work out the power and use that for a basis. For example, say you weigh(with bike) 100kg, you've just done 10 miles in 41 minutes(2460 seconds). This would give you a power figure of 246 and you just use that to mess about. The formula would look like:-

Time = (246*100)/10 in this example result is 2460 or 41 minutes
each kg taken off the total weight reduces the time result by 24.6 seconds.

I know this isn't precise but it's detailed enough to enable you to do some basic calcs and set targets. By assuming the power figure, 246 in this instance, then you're attributing everything else to weight. Yes terrain and you're fitness will vary but you could look at it as a %age gain goal. So for every kg you lose you expect to improve your speed by 1%(see how I've kept it all round numbers)

 

[I am Spartacus]

That's the fella, but just how much time?

You are trying to evaluate speed and time reduced in commuting in relation to pwr ?
That not what it is there for.
Increase your 'fitness' and you may indeed 'go quicker'.
Expensive way of training as power meters are not cheap sadly.
Highly effective tho'

 

[Panter]

Thanks guys, and some great forumulae(sp?) there MacB but I'm not even thinking of getting that advanced, it really was hypothetical.

You see, this morning whilst wheezing to work, I was deep in thought about things, and life in general, and started getting irritated about my lack of weight loss.
As the hill steepened, I felt even more annoyed as I started gasping for air and my legs started burning (as usual.)

I then started thinking about just how stupid and pointless doing all this cycling is if I can't get my calorie intake right as I'm hauling all the excess weight around needlessly.

So, I just started wondering how much easier it would be if I weighed nKg less.

I know that I could increase my fitness and make life easier, but at the moment I'm just trying to reduce my weight. Training can follow when I'm not trying to move the equvalent weight of a Ford Fiesta uphill with mere pedal power as it seems so pointless at the moment.

All I was wondering was, if I lose my 10Kg target, will that relate (roughly) to an equivalent % of weight loss in reduced power required or in reduced time given the same power output.

 

[MacB]

I understand exactly where you're coming from and, as you've realised, attributing speed gains to weight loss is far from simple.

If you're just trying to lose weight and get quicker then some form of intervals and close monitoring of diet is the answer. 2 days a week attack the commute like a time trial, give it your all, get out of the saddle and hammer every hill. Your cruising speed will increase pretty quickly.

Foodwise you need to think about volume and type. Cut your intake a bit and eat balanced meals, for snacks use fruit and nuts. Sunday to Thursday avoid any form of junk or processed food. Friday and Saturday relax a bit and treat yourself. The weight will fall off and it gets easier after a couple of weeks. But the first two weeks will take a bit of will power and dedication.

 

[Davidc]

Gets worse if you also assume that in losing 10kg you'll have lost more than that of fat and put some back as extra muscle, while also improving muscle tone and stamina!

You'll be up that hill in 30 minutes soon!

 

[Panter]

Thanks for that, appreciated.

To be honest though, I've decided to tackle the two things seperately. As I'm SO overweight, it seems pointless trying to develop the power needed to give me a performance increase.
As it is, my quads are so large that when I flex them, they go square and I've got calves that Arnold Schwarzanneger would be proud of
If I currently had the power to get me up a hill at a decent rate I think I'd be rivalling a Range Rover on Co2 emissions

The plan is to lose weight through the Winter, just by steadily getting the miles in and then try to do some training come Spring when I'm, hopefully, a lot lighter.
I've lost a stone so far, so it is working, I was just wondering how much easier my commute would've been if I'd stuck to other goals and was 10Kg lighter.

 

[Panter]

Gets worse if you also assume that in losing 10kg you'll have lost more than that of fat and put some back as extra muscle, while also improving muscle tone and stamina!

You'll be up that hill in 30 minutes soon!

Sounds good to me

 

[Garz]

Until your a sinsible weight panter I would hedge away from other distractions like power, av speed and the like. Focus instead of longer and longer rides slowly upping your frequency in number of rides.

This is hard as already with darkness and the rain my weekends have become more invaluable, so maybe a turbo so that you can guarantee some mileage being done. Whilst your in this fat stripping phase you need to give two areas a big push, these being eating smart and increasing hours in the saddle.

Oh and I forgot to mention the big one.. time. Don't expect immediate results, but the gains you make will stick better if you do it gradually. Good luck with the program!