VAM

FROM CYLINGPOWERLAB

Velocita Ascensionale Media (average velocity of ascent, metres per hour) is a rule of thumb metric of riders climbing ability developed by Doctor Michele Ferrari  since 2003. Given 2 simple pieces of information: ascent (metres), and time it allows comparisons of climbing performances, typically in terms of significant mountain ascents, while avoiding the complexity that goes into model based power estimation. With one more piece of information, average gradient, it can be extended to estimate riders wattage per kilo although it has to be stressed that these are truly “rule of thumb” estimates. 

VAM is best illustrated with an example. Imagine a rider ascends Alpe d´Huez (starting altitude 744 metres, finishing altitude 1815 metres, total ascent 1071 metres) in 40 minutes. His VAM = metres ascended x (60/minutes) = 1606 metres. 

VAM tends to be higher on steeper gradients so the extension that estimates Relative Power (watts per kilo) relies on a gradient factor relating to the average gradient of the climb. This gradient factor is defined as 2 + (%grade/10), in the Ape d´Huez example 2+(8.1/10) = 2.81. Relative Power is then calculated as VAM / (Gradient Factor x 100), in the example 1606 / (2.81 *100) = 5.72. 

Clearly VAM can be calculated very quickly and represents a simple but intuitive way to compare climbing performance. Its weakness include the bias toward steeper gradients (it would undoubtedly be easier to achieve a high VAM on the extreme slopes of El Angliru as compared with a gentle alpine climb) and possible distortions due to abundant hairpins, false flats or minor descents occurring in the ascent being analysed. 

As a way to compute “watts per kilo” VAM is useful, better than nothing, but understandably less accurate than a real power model. The VAM & VAM-Relative Power model on this page therefore includes comparative watts per kilo numbers computed from the power model used elsewhere on this site and this acts as an interesting sanity checker for the VAM based numbers.

Inputs

Time. Specify the ride time in minutes and seconds.

Start Altitude (Metres)

Finish Altitude (Metres)

Gradient (Percent). eg. 8.

Headwind/Tailwind (Kph). Specify an optional head or tailwind effect in Kph.

CdA. This is the metric of aerodynamic drag (Coefficient of drag x frontal Area) applicable to the rider and bike combined.

CRR (Rolling Resistance). Select the coefficient of rolling resistance applicable to the course. The dropdown is a handy way to select typical values.

Rider Weight (Kilos). Input the rider weight. The power model will assume an extra 7 kilos for the bike.

Assumptions (Applicable to the Power Model)

Air Pressure 1013 mb

Temperature 20 Celcius

Humidity 20%

700x23 tyres

Power measured at the crank, drivetrain efficiency 97.6%

Outputs

Ascent (Metres). A simple calculation of Finish Altitude - Start Altitude.

VAM (Metres per hour). The riders average rate of ascent in metres per hour.

Relative Power (Watts per Kilo). This is the estimate based on Dr. Ferrari's Formula Relative Power = VAM/(Gradient Factor * 100).

Actual Distance. Computed from the specified gradient.

Model Watts:Kilo. Power to weight ratio using power calculated by the model and divided by rider weight.

Actual Watts. The power calculated by the model.