This Space for Rent

« If I won the lottery, this is what I’d do · A brevet too far »

I don’t really trust my GPS

It claims that the Barlow 300k (or at least the subset that I rode before I froze to death) has 18,000 feet of climbing. If true, that would be impressive, except that I stopped a couple of times during the day and watched the GPS claim with a straight face that I was first going up 50 meters, then down 80 meters, all over the course of about 2 minutes.

14,000 feet sounds believable, maybe, but the Garmin 205 doesn’t seem to have a very good “enhanced 3d” mode on it. (It also tends to drop readings when it’s obstructed, but that, fortunately, doesn’t appear to do more than a 1-2% underreading of the distance I’ve travelled.)

—orc Mon Sep 28 22:43:48 2009

Comments

Any GPS without WAAS sucks for elevation changes. It’s just a matter of the geometry.

Paul Tomblin Tue Sep 29 05:15:48 2009

Even 18 kfeet is less than 6 km; 6 km total elevation change over 300 km is an average grade of 1 in 50, which doesn’t seem inherently implausible for mountains.

Graydon Tue Sep 29 07:42:36 2009

Except that the 300km includes two transits of the mountains, so it’s only about 180km of climbing. Barlow Pass is at ~4100ft, and the Timothy Lake transit is at ~3600ft, so there’d have to be another 10kft of upping stuffed in there. There’s certainly another 2kft in there (The 600-700ft drop from Sandy down into the Clackamas river valley, the Barlow Trail up near the summit goes down into a couple of fairly substantial river valleys (200ft, 500ft?) and there are a couple of substantial dips on the other transit, but even that doesn’t add up.)

And if the GPS was accurate, it would mean that I did 180km of climbing at an average 3% grade. I was able to get on the bicycle the next day and ride home, so I think that might be a bit high.

David Parsons Tue Sep 29 09:00:08 2009

Is your GPS claiming 18 kfeet total elevation change, 18 kfeet lowest point to highest point (I hope not), or 18 kfeet total accumulated elevation change going up?

Total elevation change would presumably count down as happily as up; I just did the BoE assuming one long slope because that’s simplest. (There are bike lanes on the highways in BC, because there’s no other road through there in a lot of cases; some of them have signs that say things like “next 40 km, 8% grade”, which makes me wonder how many cyclists try it and don’t make it.)

Graydon Tue Sep 29 13:31:37 2009

Comments are closed