Saturday, August 1, 2020

Actual Miles May Vary

People often seem a bit doubtful when I tell them my regular bicycle commute from Ferndale to the Cordata shopping center in Bellingham is about eight miles each way. I'm not sure why, unless non-cyclists can't see how someone could ride so far then put in a full work day. Or whatever. But lately I've found there is real uncertainty about the distance.

When I first started commuting on my road bike with 700x25mm tires, the distance by my odometer was around 8.2 to 8.3 miles, until I got sloppy for a spell and let my tires go soft. Then I noticed the distance was creeping up to more like 8.5-8.6 miles. When I pumped up the tires to their usual firmness, the reading settled back down. Now I am riding my old hybrid with thick, knobbly 700x32mm tires and the distance on my odometer is down to only 7.5-7.6 miles.

Odometers use pre-set wheel measurements like 26in, 27in, 700mm, etc., and have a sensor on a spoke to count wheel revolutions, then calculate ride distance and cumulative distance, as well as current speed, average and maximum speed. The wheel measurement is the wheel diameter, but the circumference of the tire (obviously) can vary quite a bit, adding up to as much as a mile of difference in seven or eight miles, whichever it is I'm really riding. I suppose that means the speed calculations aren't very reliable either.

At least now I can explain that I'm not exaggerating - with more detail than most people would want to hear. Then they'll be sorry they doubted my word.