I’ve noticed over the past few months that when I’m driving my car at ‘posted speeds,’ I’m basically riding with traffic. Sure there are a few drivers going faster than I am, but it’s not the majority. On the other hand, when riding the bike with similar road conditions, I seem to have to ride at about 10 mph faster than the posted speed limit to get similar results. It seemed odd, so I’ve been thinking about ways to validate the speedometer. Granted the best way would be to get the bike on a controlled range and use timing lights or other means to validate the speed, but I don’t expect to have access to such a setup with my resources any time soon.
On the other hand I do have several devices that I can get a very close approximation of my speed by using gps tracking. The problem of course is that I really don’t have a way to mount any of them to my bike.
A couple of months ago I decided to upgrade my cell phone. There’s nothing fundamentally wrong with the phone that I have been using. It works as a cell phone, and I can still use it as a web tablet and the rest of the features other than phone and cellular data all work, but it’s a first generation Android device, the carrier isn’t going to be updating it to current versions of Android any more and I was looking for something newer. Along the way though I have picked up a number of applications and a few accessories for the phone. Including an armband for using the phone while working out as a media player and workout tracker.
One of the first applications I installed on the old G1 phone, all of a year and a half ago was a gps based speedometer.
As I’ve noted elsewhere, I do very much dislike housecleaning. However in rummaging around through my ‘Too be reviewed for discarding’ baskets this week, I found the arm band for the phone. My new phone also fits in the arm band, but I’m not sure I want to have that phone hanging on my arm while riding. Granted it’s not exactly highly protected where I do carry it, but it seems to stay put, so I’m comfortable with leaving it there.
One of the problems with both phones is that they are hard to read in direct sunlight. So using the speedometer for the trip to work at 6 pm or home at 6 am, has it’s problems. However I do have one night of the week wehre my work shift starts at 2 am. Yeah, that kind of sucks, but it helps pay the bills.
It does have one advantage though. It’s dark. Or at least as dark as things get when the sky is overcast and I live in a major metropolitan area. It’s dark enough that the screen shows up clearly.
So, got ready for work tonight. jacket on, phone in the arm band, all set up to start the GPS speedometer. That does include making sure that the phone is oriented so I can read the display without having to envision myself flipping to see the screen. Not exactly the imagery I want to have while riding down a freeway at 55 miles per hour or so. I presume you can imagine why.
In any case, I get onto the freeway and get up to what feels to me like highway speeds, look down at the speedometer on the bike, it says I’m doing about the mid 60s. Look down to the arm, which says I’m doing 55.
As I get to part of the commute that the speed limit is 40, I drop down to the very low 40s on the bike speedometer and I get a reading of 38-40 on the cell phone. So it appears that the bike speedometer is reading about 10% high. I suppose if I don’t want to worry about getting a speeding ticket, that can be helpful, but that seems odd for a bike. And before someone suggests that it’s low tire pressure, or that it is probably wear on the tires, reducing the circumference of a tire by 10% pretty much brings the bike down to it’s wheel. I’m pretty sure I would be having some serious control issues by then.
Considering that the rims appear to be stock, and I don’t think anything has been done to the drive train, that suggests that someone swapped out the tire with one that is noticeably different in size.
Well, I’ve had the bike for over 2 years now. It’s probably time for me to replace the rubber anyway.