Predicting Climb Times

After reading Daniel Connely’s blog post on the effect of road grade on VAM, I thought I’d try using my Strava data from last weekend to predict my climb times this weekend.

Taking liberties to simplify Daniel’s work, I will use my data from the Cavedale climb last weekend to predict my time on the Orr Springs climb this weekend. These climbs are both Cat 2’s and similar in length and average grade. This exercise is really only interesting because I don’t ride with a power meter. Instead, I’ll attempt to ride both climbs at the same perceived effort.

Here’s my Strava data from Cavedale:

Step 1 – Relative Power

Calculate relative power in Watts/kg on Cavedale.

Gradient factor = 2 + (% grade / 10)
2 + (7.3% / 10) = 2.73

Relative power (Watts/kg) = VAM (meters/hour) / (Gradient factor * 100)
1066 / (2.73 * 100) = 3.9 W/kg

Step 2 – Relative Power to VAM

Calculate expected VAM on Orr Springs.

Convert from relative power to VAM:
VAM = Relative power (Watts/kg) * (Gradient factor * 100)
3.9 * (2.79 * 100) = 1088

Step 3 – VAM to Ascension Time

Calculate expected time on Orr Springs.

Convert from VAM to ascension time:
Minutes to ascend = (meters ascended * 60) / VAM
(490 * 60) / 1088 = 27 mins


27 minutes. It’s practically done!

I’ll give Orr Springs a go this weekend and report back.

[1] effect of road grade on VAM on
[2] Velocity Ascended, Metres per hour on Wikipedia.
[3] Uphill Gradient and VAM on 53×

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2 Responses to Predicting Climb Times

  1. Dave Watts says:

    looks good-the math seems pretty solid….but the unknown x should be applied to account for anything from bubblegum all over the road to a bad hangover to human error to a great ride-give the x-factor a minus .10 to a plus .10 leaving a time from 24′ 30″ to 29′ 30″…..Good luck…looking forward to seeing you this weekend…

  2. Vitaly says:

    One thing, for your perceived effort to be accurate, you have to expend the same amount of energy getting to that climb as you did to the one you used for comparison. I’m very curious to see what you come up with. I hope that you won’t mentally push yourself too hard trying to get those 27 minutes, that would just skew the experiment =).

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