More about VAM
08 Jun 2007
We have seen how to measure the VAM and how this parameter is influenced by the grandient of the climb and by altitude (see the Articles).
Other factors, related to the characterisics of the road or to race situations can also become very determining.
Not only the direction of the wind, but also the road pavement (more or less "rough") can significantly reduce the VAM even up to 6-10%.
A climb with many hairpin bends does reduce the VAM too, because the cyclists is forced to decrease the power output on the pedals on the tight curves.
The VAM values recorded for example on Alpe d' Huez are penalized by the high number of bends, in comparison with other climbs with less changes of direction.
Lightest athletes suffer less the accelerations when coming out of the curves, but at the same time suffer headwind conditions much more than heavier riders.
At a speed of 20 km/h, a headwind blowing at 2 m/sec (7.2 km/h) increases the power output needed to keep the speed by about 50 watts: for a cyclist of 58 kg climbing at 350w (6 w/kg), this corresponds to 14.2% of the expressed power, while for a cyclist of 70 kg climbing at 420w (6 w/kg) this represents only 11.9% of the power.
In group races it's important to notice how the strongest teams take the first kilometers of the climb with the "gregari" giving it all-out, while the leaders draft: drafting at 24 km/h from a single rider lets you save about 40w. The advantage is even bigger if you pedal covered by a small group of riders.
Obviously, smaller and lighter cyclists can profit more from drafting.
This important advantage of drafting while climbing also explains why VAM values measured on uphill TT events, which only last a few dozens of minutes, are usually inferior to the VAM measured on the same climb performed with the peloton, even if at the end of a several hours stage.