Friday, January 29, 2010

Less Weight Analystics

Yesterday's "No More Spaghetti Bolognese" has a quote from João Correia in which he says, "During the rides you’d be going up a hill and pretty soon you’re dropped, you’re gone, you’re not even in the group anymore.”

Personally, I'm terrible about the analytics as they relate to cycling. I'm more of a just go out and ride kind of guy. No HRM, no computer, no Garmin, no Powertap, etc. Nevertheless, I was curious to see what I could find out about how significant weight loss is and found where you can find modeling tools to determine all kinds of things.

They have a calculation model for determining the benefits from less weight here. Accompanying that calculation model is this text (and the chart at the top of this article):

Less weight going up a slope means faster times. How much faster?

Suppose one is considering buying a new, light-weight frame or going on a diet. What is the benefit from having less weight? How much time would be saved over a given distance on a specified slope? How much more distance would be covered in a given time?

Two riders, identical except that one has less weight than the other, ride a given distance up a hill. The the calculation gives the distance and time between the riders as the lightest rider reaches the given distance.

The plot shows the benefit from less weight when riding up a hill. The range of the plot is from -10% to +10% grade and from 0 to 5 kg less weight. The table gives specific values for the given speed.

Note that large changes may produce mathematical results, but may not have real-world meaning. Keep changes small.

"Negative values for improvements" show that weight is an advantage going down a hill. The plot shows that weight is more of a penalty going up hill than an advantage going down.

Example: Benefit From Less Weight
This Much Less Weight 5 kg
Over This Distance 2000 meters
On Hill of Slope 0.03 Decimal
Faster by 8.69 s
Ahead by 64.82 m
Frontal Area 0.5 m^2
Coefficient Wind Drag 0.5 Dimensionless
Air Density 1.226 kg/m^3
Weight Rider & Bike 75 kg
Coefficient of Rolling 0.004 Dimensionless
Power 250 watts

Wow, those seconds can add up fast on the very long climbs in Italy!



  1. I'm trying to lose just five pounds for the very reason you speak of in this blog entry. Its difficult to shave off the last pounds to get to my target! This blog entry is good motivation to push on with the goal. Thanks!

  2. I agree the lighter the better for climbing, but I'm just a recreational rider, and the speed doesn't matter to me. The main benefit to me of lower weight is making it up the climb with less effort. If it's a long day with multiple climbs, it makes a noticeable difference in how beat I feel when I get home.