Put it to the test – then test yourself!


Some cycling climbs to experiment with

If you want to try the calculator out with some familiar climbs, you can try:

Long and steadyBox Hill in Surrey: 2280m in length with 120m elevation gain (5.2% average gradient). 7 minutes is a good time.

Short and steepYorks Hill in the Kent Alps: 640m long with 82m elevation gain (12.8% average gradient). 4 minutes is a good time.

Somewhere in betweenDitchling Beacon in the Sussex hills: 1460m long with 128m elevation gain (8.2% average gradient). 7 minutes is good going.

How to use the Hill Climb Calculator to train

Once you've worked out what wattage you need to average over the duration of the effort, you can practice doing similar-timed intervals holding that power on the turbo trainer, or outdoors. (Best aim to go 10W harder, just to be sure).

If you have access to your Power Curve in Strava, or another training tool, you may see you've actually achieved the required threshold already. Look back at that ride to see if you can recall the situation and conditions that enabled you to hit that highpoint - was it on a climb, or during a sustained sprint?

Alternatively, you can use the calculator to try adjusting your weight to see how much less power you'd need to output if you were to drop a kilo or two (or drop a ton on that Enve carbon stem on eBay).

How does the Hill Climb Calculator work?

There are some simple formulas you can use to estimate the average power required for a climb. Allen Lim, who worked with Floyd Landis during the 2006 Tour de France, is credited with coming up with this formula:

Power Required (W) = Body + Bike Weight (kg) x 9.8 x Elevation Gain (metres) / Target Time (seconds)
+10% to allow for Rolling Resistance and Wind Resistance

This is a good start. We found it gave reasonably accurate results for some climbs. However, it doesn't take into account the fact that wind resistance obviously increases as you go faster, or that the power required to overcome rolling resistance increases with speed, or that your drivetrain is not 100% efficient at converting power. The following, more sophisticated, formula is used in Broleur's Hill Climb Calculator.

P = krMs + kaAsv)2d+ giMs

Where:
P = power required (in watts)
kr= rolling resistance coefficient
M = mass of bike + rider
s = speed of the bike on the road
ka= wind resistance coefficient
A = the frontal area of the bike and rider
v = speed of the bike through the air (i.e. bike speed + headwind or – tailwind)
d = air density
g = gravitational constant
i = gradient (an approximation²)

Assumptions and limitations

The calculator assumes the road surface is reasonably good, that you're on some type of road tyres and the air is still. It also doesn't account for the difference in air density between sea level and high altitude. It's very difficult to account for the wind speed and direction in making estimates like this.

The calculator will be most accurate on hills with a steady gradient. If there are major variations – and you want to get a more accurate estimate – you might want to consider breaking the climb into a number of smaller segments and then adding them up.

Comments and suggestions?

Hope you find this somewhat useful - or at least interesting! If you have any (constructive) comments or suggestions for how the calculator might be improved, let us know on Facebook, Twitter or by emailing steve@broleur.com