Reading this thread for a bit, it occurred to me that I'd done a quickie check of Racer's speedo accuracy when I first bought the bike using my bicycle GPS computer (Garmin Edge 25) but hadn't really looked at it since doing the Kinesis wheels and Conti RA3 tires. So I fitted the Garmin to the handlebar and had it monitor my ride to breakfast and to my doctor's appointment this morning, checking the speedo against the GPS MPH readout.
Here's the route and some stats off the Garmin:
A 31 mile run around the lower Santa Clara Valley, essentially, incorporating two expressway stints, a nice longish jog on the interstate highway, and some in-town doodling along.
Results are pretty much as expected: I find the speedo reads about 2 mph high at the bottom end of the range and the error grows linearly up to about 90 mph indicated where it reads about 8 mph fast. 75 mph indicated settles at 69 mph, 85 mph settles at 78 mph.
The key is now I know how far off it is across the range so I don't have to worry too much about the Highway Patrol nabbing me if I'm blasting down I-5 at an indicated 85 ... it's really only about 78, or three mph over the speed limit.
I don't mind being boring to officers of the law that way.
Good news, however, is that the speedo and the odometer seem to be calibrated independently. The trip odometer readout for the day was a little less than 1 mile off the GPS measured value, so my calculations of fuel economy and such are pretty accurate.
Fun fun fun ...
G
Here's the route and some stats off the Garmin:
A 31 mile run around the lower Santa Clara Valley, essentially, incorporating two expressway stints, a nice longish jog on the interstate highway, and some in-town doodling along.
Results are pretty much as expected: I find the speedo reads about 2 mph high at the bottom end of the range and the error grows linearly up to about 90 mph indicated where it reads about 8 mph fast. 75 mph indicated settles at 69 mph, 85 mph settles at 78 mph.
The key is now I know how far off it is across the range so I don't have to worry too much about the Highway Patrol nabbing me if I'm blasting down I-5 at an indicated 85 ... it's really only about 78, or three mph over the speed limit.
I don't mind being boring to officers of the law that way.
Good news, however, is that the speedo and the odometer seem to be calibrated independently. The trip odometer readout for the day was a little less than 1 mile off the GPS measured value, so my calculations of fuel economy and such are pretty accurate.
Fun fun fun ...
G