VAM is a term used in the world of cycling to measure a rider’s average ascent speed or mean ascent velocity.
The Italian-originated term, which comes from ‘Velocità Ascensionale Media’ and literally translates as ‘Average Climbing Speed’, was coined by the Italian physician and cycling coach, Dr Michele Ferrari, and is calculated by taking the total number of metres climbed and dividing it by the time taken to climb it.
The result is expressed in units of metres per hour, making it an objective measure of a cyclist’s fitness, speed and overall performance.
VAM is particularly important for cyclists who compete in events with a lot of climbing such as Grand Tours or hilly sportives, as it is an effective way to compare performances, predict climbing speeds and as a tool to estimate a rider’s watts per kilogram measurement.
How to work out your VAM
To calculate your VAM, you will need to record the elevation gain, distance, and time it takes for you to complete a climb.
You can use a GPS cycling computer or smartphone app to track these metrics, or use an online map with altitude and a stopwatch.
Once you have the data, you can calculate your VAM using the following formula:
VAM = (metres ascended × 60) / minutes it took to ascend
While it’s important to note that ambient conditions such as temperature, wind, and road surface, can impact your figures, VAM still gives an interesting method of comparing performances, or even calculating future mountain climb times when cycling touring with a loaded bicycle.
How to estimate your w/kg from your VAM
To estimate your power output per kilogram of body mass, you can use the following equation:
Relative power (watts/kg) = VAM (metres/hour) / (200 + 10 × % grade)
This equation takes into account the additional power required to overcome the extra mass of the bike and the friction from the road.
The higher the gradient of the climb, the more power is required, which is reflected in the equation.
To get an accurate estimate, it’s essential to have an accurate VAM value and to know the gradient of the climb used to calculate it.
Does VAM Change Between Climbs?
Eagle eyed sports scientists as well as armchair fans will have noticed the gradient of a climb greatly influences the VAM performance of athletes: the steeper the climb, the higher the VAM values developed by the riders.
In measured tests on various climbs with a rider weighing 64 kg pedalling at a steady 300 watts gave the following results:
| Gradient | VAM (m/h) |
|---|---|
| 5% | 1180 |
| 6% | 1215 |
| 7% | 1250 |
| 8% | 1290 |
| 9% | 1340 |
| 10% | 1400 |
| 11% | 1475 |
| 12% | 1565 |
| 13% | 1675 |
As you can see, the VAM values do not increase at a linear value, instead they rise exponentially with every gradient percentage increment.
What is a Good VAM?
Other Factors That Influence VAM
There are other factors that can influence your VAM results.
A windy day can make the biggest difference – both a headwind and a tailwind can effect your climbing speed. The quality of the road surface also – even rough tarmac can significantly reduce the VAM by up to 6-10%. Gravel climbs even more so.
A climb with lots of hairpin bends can reduce your VAM reading too, because of the sudden efforts needed to power through them, after already having been forced to decrease the power output on the pedals on the way into the tight curves.
Looking at Tour de France readings you can see that the VAM figures recorded on Alpe d’ Huez are lowered by the high number of bends, in comparison with other climbs with fewer changes in direction.
The skinnier lightweight athletes suffer will be less affected by the hairpin accelerations when coming out of the curves, but then will be disadvantaged by strong headwind conditions compared to the bigger, heavier riders.
Studies have shown that a headwind blowing at 2 m/sec (7.2 km/h) will affect a cyclist riding at a speed of 20 km/h, necessitating an increase in the power output needed to maintain the speed is about 50 watts.
For a rider weighing 58 kg and climbing at 350w ( the magic 6 w/kg needed for grand tours), this corresponds to 14.2% of the actual power, whereas a rider coming in heavier at 70 kg climbing at 420w ( again – delivering 6 w/kg) this represents only 11.9% of the power.
In team races you’ll often see how the stronger teams take the first section of the climb with the bigger ‘diesel’ riders giving it a solid turn, while their team leaders sit behind them drafting where they get to typically save about 40w.
This drafting advantage is even greater if it can be maintained by riding in slipstreams for even longer, covered by a small group of riders – smaller and lighter riders will gain more from the effects of drafting.
The benefits of drafting while climbing also explain why VAM values that are calculated from mountain time trial stages, which typically last less than n hour, are usually lower than the VAM readings measured on the same climb performed with the benefit of the shelter the peloton, even if at the end of epic all day stages lasting many hours.
Why Doesn’t Strava Just Show Actual Power
if you’ve got access to Strava and check the leaderboards for your favourite climbs you’ll be able to see a power value often given which is calculated by multiplying the relative power by the weight of the rider and all of their kit. If you compare the power values in any leaderboard you will see a large variation as these weights will be of varying amounts and of varying correctness, all because someone’s Power is showing 450 Watts, you might only need to register a Power value of 400 Watts to beat their time if you are 3kg lighter. You will also see a VAM measurement on Strava so you can compare your performances on one climb and predict your performance on others.
Conclusion
In conclusion, VAM is a valuable metric for experienced cyclists looking to track their progress and estimate their power output per kilogram of body mass.
It can be easy to calculate and will provide you with a relatively objective comparison of performances.
By regularly tracking your VAM, you can set goals, monitor your progress, and adjust your training to achieve your desired results.