Saturday, June 02, 2018

A new home: Watt Matters ±

From here on this blog will have a new home:

Watt Matters ±

Nothing like a nice new coat of paint to freshen things up.

Most posts in the blog archive should automatically redirect.

See you on the other side!

Read More......

Wednesday, May 30, 2018

VAM & W/kg estimates

Just wanted to post a few charts for reference.

First chart compares W/kg estimates based on the same vertical ascent rate (VAM) for each of two methods:

Dr Ferrari's formula and the mathematical model described in the paper by Martin et al:

The plot compares the W/kg estimates for each of three gradients: 6%, 8% and 10% for a range of VAMs between ~800 m/h and ~2000 m/h. A red unity line is included for reference.

To make the variances between each method a little easier to see, the following chart plots the difference between the two W/kg estimates, again a line for each of the three gradients: 6%, 8% and 10%.

I don't have a lot to add to the charts other than to say the Dr Ferrari formula is a bit of a quick and dirty way to estimate W/kg from ascent rates but it does not consider a range of variables included in the Martin et al formula.

In particular we can see the estimates can vary quite a bit depending on both gradient and on VAM.

Same plot as above but this time with the variance expressed as a percentage of the Martin et al method estimate:

I would certainly place more faith in the Martin et al method, and that was also the conclusion of this paper by @ammattipyoraily and @veloclinic (Dr. Mike Puchowicz) which examined the different methods of calculation compared with actual power meter data from a large number of data files.
Estimating climbing performances of professional cyclists: a larger dataset

For consistency with the analysis in the paper above I chose rider mass and CdA in the middle of the range from that paper. I do not know what Crr assumption were used though. I settled on 0.005.

A Crr value in the range 0.004 to 0.005 would be typical and the impact on calculations of a difference between 0.004 and 0.005 is equivalent to adding 0.1% to gradient (and an associated bias error in W/kg estimates of about the same order).

Read More......