Wednesday, July 20, 2011

l'Alpe d'Huez - one for the mortals

About this time last year I posted this item about ascent times of leading professional riders up l'Alpe d'Huez and what power to body mass ratio would be required to do that.

There's a chart which shows the relationship between ascent time and power to body mass ratio (watts per kg - W/kg). It also provides an indication the impact of wind can have on climbing speeds.

Times for leading riders since 2001 are shown on the chart.

The guys over at the Science of Sport blog referenced it in a post here, after seeing it on a cycling chat forum I posted to recently.

Well for a bit of fun (and considering the Tour de France is heading up the Alpe in a few days), I thought I'd post a follow up chart which covers the power to body mass ratio for the rest of us mere mortals.

Here it is (click to embiggen):

It's not a hard chart to read.

Want to ride up l'Alpe d'Huez in 1 hour dead? Then you'll need to be able to sustain around 3.75 W/kg, give or take depending on the wind. If you are 70kg, then that's around 260-265 watts.

If you know your sustainable power is 3.4W/kg, then you can expect to get up the Alpe in around 66 minutes.

In calculating these values, I've made a few assumptions (listed on the chart), although the relationship between speed and W/kg on steep climbs is not particularly sensitive to those assumptions.

After power and mass, wind has the biggest impact on speeds when climbing. Hence the two extra lines for head and tailwinds.

At my best form*, I would expect to climb it in around 56 minutes.

How fast have you been up l'Alpe?

* My power to body mass ratio for 1-hour at best is ~ 4.2W/kg (based on my racing power at the UCI World Cup this year), but I have to allow a bit of extra mass for my prosthetic leg. I'll get to do it one day.


TimeMachine said...

Great post Alex - also brings back recent fond memories for anyone who has just done the Etape or the Marmotte.

BTW, there is a mass start weekly race up AdH every Thursday morning 10 am from June to September if any mere mortals want to do some field testing ;-)

Anonymous said...

I did 53.12 two days ago. Do you know what time sprinters like greipel and kittel had during tdf this year? Christian

Alex Simmons said...

I've no idea.

Kevin said...

50:51 on 330 Watts at about 75kg in 2010 for me which matches your chart pretty well.

Regarding one of the comment questions I know that my time would not have made the time cut in the Tour de France ITT that Armstrong won. Zabel was 7 minutes faster I believe. Lots of EPO in that peloton, but still pretty humbling.

Ryan Brook said...

Very interesting Alex. Thanks for posting the chart.

How would you calculate the Power to weight for this chart. Many people use the 20 minute threshold test on a watt bike. Would you need to get you 60 minute power for your calculations?

56 minutes with a prosthetic leg. Wow! Very humbling!

Alex Simmons said...

Given the power-duration curve is pretty flat in the range from 50- to 70-minutes, then a good estimate of your functional threshold power would be reasonable place to start. As to what proportion of 20-min power that is, well that's individual, anywhere from 91%-96% is about right.

I haven't had the chance to climb AdH, only estimate what I could do in peak form. That's unlikely to happen any time soon though!