How (much exactly) does power:weight ratio convert into speed?

[RoboLuke]

MTB related.

 

Not a complicated question, but I don't think an obvious answer.

 

If one obtains a power:weight ratio improvement of 10% - what % speed improvement would this render?

 

1. On the one side I'm thinking that power:weight does not consider wind resistance...so a 10% P:W would be - say 7 % speed improvement.

2. On the other side a better P:W ratio means that the legs have less stress, and should thus last longer...and over a proper distance render a better time. Maybe even better than 10%.

 

Does anyone have some facts/real experiences to share?

And if you just feel like giving an subjective view - then OK, but please just let us know that you are philosophy-ing.

[jaaki]

In cycling there can't be any real scientific studies because there are too many variables. imho

[Dubber]

MTB related.

 

Not a complicated question, but I don't think an obvious answer.

 

If one obtains a power:weight ratio improvement of 10% - what % speed improvement would this render?

 

1. On the one side I'm thinking that power:weight does not consider wind resistance...so a 10% P:W would be - say 7 % speed improvement.

2. On the other side a better P:W ratio means that the legs have less stress, and should thus last longer...and over a proper distance render a better time. Maybe even better than 10%.

 

Does anyone have some facts/real experiences to share?

And if you just feel like giving an subjective view - then OK, but please just let us know that you are philosophy-ing.

 

I don't think point 2 is true. As the saying goes, it never gets easier you just get faster. So, yes, if you maintain you standard speed your legs would do less work, but that's not what you are after. With greater power you end up cycling faster - so you legs still work at their 'max'.

 

No facts to back this up though...

[BrandonF_]

Red line it, ALways.

[TopFuel]

In cycling there can't be any real scientific studies because there are too many variables. imho

 

Absolute rubbish. Of course you can (and thus do) have a myriad of studies conducted on the cycling population. It is actually quite easy to control for a specific variable if you have the understanding of the physiology of exercise and a carefully thought out hypothesis in mind.

 

People like Dr. Jeroen Swart, Prof. Tim Noakes and Dr. Ross Tucker have built their careers on the studies that you claim cannot be conducted.

[jcza]

Very complicated subject with just as many opinions.

 

You need to use power output and weight to express w/kg. When dropping weight you will increase the w/kg numbers but if you drop too much weight you wil in all likelyhood also lose some power.

 

Going fast on flat requires more aero and much more effort. Going faster uphill is simpler (not necessarily easier) but because of gravity less weight makes you faster immediately.

Edited March 29, 2014 by jcza

[TopFuel]

I agree with jcza. Anecdotally, I would say that better power to weight will show as increased speed more on uphill sections where wind resistance plays less of a role.

 

It will no doubt improve your speed on the flats as well, but will probably be more noticeable on the up hills. Especially considering the not so insurmountable force that is aero resistance.

[Lone Rider]

Exactly what was said - the steeper the gradient the more advantage the rider with the higher power/weight ratio will have.

 

On flat terrain, the cyclist able to put out the most power will have an advantage, irrespective of weight (assuming they've both got the same drag coefficient).

 

...and on downhills the heavier cyclist will have a slight advantage.

 

http://theclimbingcyclist.com/gradients-and-cycling-how-much-harder-are-steeper-climbs/

[jaaki]

Absolute rubbish. Of course you can (and thus do) have a myriad of studies conducted on the cycling population. It is actually quite easy to control for a specific variable if you have the understanding of the physiology of exercise and a carefully thought out hypothesis in mind.

 

People like Dr. Jeroen Swart, Prof. Tim Noakes and Dr. Ross Tucker have built their careers on the studies that you claim cannot be conducted.

 

 

Sure you can control the gradient of a hill on a treadmill and using the same athlete in back to back test in the lab, with the athlete knowing their exact fitness level (higher levels show less gains for more improvements)

but unfortunately it doesn't allow for variables like trail (line choice) , temperature and wind variations, air density and whatever else can change.

Only knowing all variables, can you safely say that an increase in p/w will yield X improvement.

Edited March 29, 2014 by jaaki

[Six13]

I read a book about Armstrong's training (yes, he did do some training :-) ) they mentioned a formula for him about his weight to power ratio and what he could achieve as he lost weight during the tour.

[TopFuel]

Sure you can control the gradient of a hill on a treadmill and using the same athlete in back to back test in the lab, with the athlete knowing their exact fitness level (higher levels show less gains for more improvements)

but unfortunately it doesn't allow for variables like trail (line choice) , temperature and wind variations, air density.

Only knowing all variables, can you safely say that an increase in p/w will yield X improvement.

 

Actually, the do control for those variables in studies. By using the same athlete, in the same conditions, using the same equipment, doing the same test, you can easily control for a single, specific variable and calculate a meaningful and statistically relevant result.

 

No scientific test is 100% accurate, most work to within a 95% confidence interval, and aim to get that interval as tight as possible, as well as using other statistical tests to show benefit or harm.

 

Also, frankly extraneous variables like line choice are fairly obvious and actually play little role in determining how fast an athlete will go depending on the controlled variable, within the context of a laboratory study, where such variables do not exist.

[The Crazy German]

http://www.analyticcycling.com/ForcesSpeed_Page.html

 

great site I blame my big bones for weight and wind resistance

[jaaki]

Maybe a test you can do.

 

Calculate your own power/weight ratio, weight being you and your bike and then ride a section of trail...

 

Step two is to add enough weight to your bike to make your power/weight ratio 10% worse and then repeat the test.

 

Please post your results.

[RoboLuke]

eezz....jaaki

now that is a practical test ...but a horrible one

Holding out for a hub answer :-)

[TopFuel]

Maybe a test you can do.

 

Calculate your own power/weight ratio, weight being you and your bike and then ride a section of trail...

 

Step two is to add enough weight to your bike to make your power/weight ratio 10% worse and then repeat the test.

 

Please post your results.

 

The website above will do that for me, using mathematical models that they have calculated over thousands of cyclists, not just one (which is statistically speaking, irrelevant).

[Christie]

On a climb, power to weight ratio is the dominant factor that influence speed.

 

On a flat, it is power to drag ratio.

 

(I hope we do not see deep section mtb wheels and aero tubes soon, though)