The map lies.

14 12 2009

I discovered something rather annoying a week ago when I attempted the Wagga Three Peaks Challenge. The hills were a lot steeper than I had remembered or expected. I always plan any new ride in advance with, one of those online mapping sites that shows the elevation. For a new rider, I like to know what I am in for, especially as it helps me get my head in the right place.

During the ride I remember thinking that the map classed this as an 11% grade, and I knew I could overcome a 7% grade. The problem was, it felt much steeper. It had to be at least double the grade of the first “peak” but the map elevation graph said otherwise.

So on returning home, and after a much needed shower, I did a little investigating. Here’s what I found.

When I mapped my for the first peak, the elevation profile told me that the maximum incline was 11%. I knew I had overcome an 11% grade before, so I wasn’t too concerned. However, in mapping the run, I set my start and finish points at the beginning and end of the road respectively. Problem is, the elevation profile was giving me an average grade. When I remapped using the start as the beginning of the steep bit and the end as the peak, the elevation profile spat out a maximum grade of 20%, far steeper than anything I had attempted before.

I have included below three maps which demonstrate this point (probably better than my above attempt). As you progress from map 1 to 3, note how the “grade” changes for the same stretch of road. Just click on the pictures for a better quality image.

Map 1 - Maximum Grade 20%

Map 2 - maximum Grade 15%

Map 3 - Maximum Grade 11%

So lesson learned…now when I plan a ride, I will be careful to not only plot an elevation across the whole course, but also for individual hills (in a step-wise fashion). Or, if you prefer, just go for a drive and look at the hill first.

This may be common sense to the seasoned rider, but for a newbie like me, it was a revelation.

By the by, the first hill (which I struggled with for a couple of months, has an average grade of 7% but a peak grade of 13%.




One response

19 12 2009

Thanks for the idea. It hadn’t occurred to me to map only a portion of my ride. Turns out that a tough hill on one of my routes has a 16% grade near the top. Wow. I was thinking 10 or 11.

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