W/kg

A light bike doesn't replace good fitness.

Moderator: Moderator Team

Post Reply
User avatar
Kermithimself
Posts: 1013
Joined: Sat Jun 02, 2007 12:48 pm
Location: Denmark

by Kermithimself

A friend of mine recently asked me a question that I was uncertain of, so I'll try it here with all the brains.

If rider A and B rides up a climb in exactly the same time, and with the exact same weather conditions, will they have the same Watt/kg? If rider A weighs 70 kg, and rider B 80, and rider a rides with a powermeter. At the top rider A has had an average wattage of say 300 watts. This equals to 4,28 Watts/kg. Would you be able to take rider B and say 4,28 x 80 = 342 watts?
------------
If you dream of being famous - think of what birds do to statues.
Instagram: https://www.instagram.com/kermithimself/
Youtube: https://www.youtube.com/channel/UCdCPaXwpeXT_LpuEF0REjqw
Facebook: https://www.facebook.com/gotlegscycling/

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



darkblue08
Posts: 79
Joined: Wed Aug 17, 2011 12:56 pm

by darkblue08

No, there are many factors that influence the time/speed, but all being equal: There should be a surtain grade were the are the same. I just dont know what that grade is.

xcforme
Posts: 33
Joined: Fri Sep 18, 2009 5:17 pm

by xcforme

http://www.training4cyclists.com/how-much-time-does-extra-weight-cost-on-alpe-dhuez/

Here's a fun little experiment showing how much weight and rolling resistance will affect performance.

Apparently, on Alpe d'Huez, 1,8 kg of extra weight equals 1.54 min time difference.
More interestingly; riding it with a tire pressure of only 3 bars is just 1 min slower.

To answer your question --> It depends on the gradient.
Very steep: Time depends almost entirely on relative power (W/kg)

Geoff
Posts: 5395
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

Interesting question, but I suspect power is non-linear.

pwork
Posts: 19
Joined: Wed Mar 02, 2011 7:12 pm

by pwork

Geoff is correct, but with a bunch of assumptions, you're not far off. I came up with 338.59W using the following equation (p=kg*m^2/s^3). I made an excel sheet for my wife and I when we only had one PM to do the same thing, and the results seemed reasonable and later confirmed w/i small %.

For your inputs, and my output, the following assumptions apply:
-bikes and gear weigh the same
-rolling resistance is the same.
-Cd is the same or that the speed is so slow it doesn't contribute.
-Riders were side-by-side over the climb.

Post Reply