Thankfully I was never asked that question while riding my motorcycle. If I had been, I could legitimately respond with: “not a freaking clue.” You see, my motorcycle hasn’t had a functioning speedometer for as long as I have owned it. I was finally spurred to fix it when my tachometer needle decided to fall off inside the gauge. One broken gauge I could ignore - but not two!
For the tacho needle, I simply snagged a few needles from various cars at the junkyard and tried a few of them until I found one that fit, and cut it to an appropriate length. The speedometer was not worth fixing, however.
My speedometer is a cable-driven unit and it makes terrible noises while bouncing madly from 0 kph to 200 kph, all while cruising comfortably with traffic on the highway. I have had it apart, and I have decided there are two problems: the spring that acts as resistance to the needle has weakened with age, and the bearing that gets spun by the cable has thrown in the towel. Honda no longer makes these parts, and the only speedometer specialist in town won’t touch motorcycle speedometers, oddly. I’m sure I could eventually hack something together out of another bearing and another spring, but in this case I just went for a quick, cheap and reliable solution.
Motorcycle speedometers are not known for their accuracy. For this reason, it is a fairly well-known upgrade in the motorcycle community to add a secondary speedometer in the form of a bicycle computer. Now, I’m not sure who are these daredevil bicyclists who regularly exceed 99 kph, but apparently there are enough of them that several manufacturers of bicycle computers will actually include a third digit in their displays. Sigma computers are known to work well on motorcycles, and so I found a Sigma BC-509 bicycle computer on Ebay for $7 shipped.
I needed the following features to make it work as a complete replacement for my cable speedo:
Pulling out the old speedometer was fairly easy. With the front cover off, only two bolts on the back and the speedo cable need to be removed. The other end of the cable was unscrewed from speedo drive on the front wheel, and a small plug in its place keeps the dirt out of the speedo drive gear.
On to mounting the bicycle computer. The computer itself would live in the familiar speedometer location. For this I cut out an aluminum plate to fill in the space and to hold the speedo. It took some trial and error trimming to get it to fit properly.
I had planned on using two-sided tape to secure the plate in place, but it held itself in place quite well with friction. The speedo itself is simply screwed on to this plate.
Note the grommet to keep the sharp plate from severing the wire.
With the cover in place, it was bvious that the shiny aluminum needed some black paint.
A few coats of paint and a few days later…
…the silver square still stands out against the black circles, but less so with a black background.
The other half of the speedometer is the pickup cable. This is normally tied to a bicycle fork leg with an elastic band, but this wouldn’t work on a bike due to the larger fork diameter and the greater forces involved with hitting potholes at 60+kph.
I carefully drilled two holes in the sensor and threaded through some black zip ties:
This could now be attached to the fork leg.
The sensor is triggered by a magnetic pulse, but the magnet included with the speedometer is designed for bicycle spokes and won’t work here. I first tried a random old magnet I had laying around but it proved too weak to trigger the speedometer sensor. A pair of old headphones gave up their tiny-but-powerful magnets instead, mounted to the front brake disc carrier. A little glue is extra insurance, but the magnetic force does a pretty good job holding the magnets in place.
For most motorcycles the cable attached to the computer isn’t quite long enough to reach down the fork leg, but with my little Ascot it was the perfect length. I made sure to have the forks completely unloaded before installing the cable. Otherwise, the cable might break when the forks extend to their full length. With a little more cable length I probably could have hidden the wire better (or run it along the brake line), but it’s not terribly hideous.
Once everything is installed the computer needs to be set up. I needed to program the time, total odometer reading (34,000km on this bike!), and wheel circumference. This is done according to the amazingly multi-lingual instruction booklet. Note that it’s not a speedometer, it’s a Funkclok. I think I’m okay with that.
I measured the circumference with a string around the tire, and came up with 1970mm:
A quick test ride showed me what it was like to know my speed while riding my Ascot. I no longer have to guesstimate my speed at Calgary’s many speed cameras! The only downside to this model is that it has a fairly slow refresh rate - it only updates the speed readout every couple of seconds. No biggie - it’s still way better than trying to guess your speed based on the traffic around you.
Cost:
$7 - Sigma bicycle computer
Incidental supplies:
magnets from old headphones
zipties
aluminum
grommet
For the tacho needle, I simply snagged a few needles from various cars at the junkyard and tried a few of them until I found one that fit, and cut it to an appropriate length. The speedometer was not worth fixing, however.
My speedometer is a cable-driven unit and it makes terrible noises while bouncing madly from 0 kph to 200 kph, all while cruising comfortably with traffic on the highway. I have had it apart, and I have decided there are two problems: the spring that acts as resistance to the needle has weakened with age, and the bearing that gets spun by the cable has thrown in the towel. Honda no longer makes these parts, and the only speedometer specialist in town won’t touch motorcycle speedometers, oddly. I’m sure I could eventually hack something together out of another bearing and another spring, but in this case I just went for a quick, cheap and reliable solution.
Motorcycle speedometers are not known for their accuracy. For this reason, it is a fairly well-known upgrade in the motorcycle community to add a secondary speedometer in the form of a bicycle computer. Now, I’m not sure who are these daredevil bicyclists who regularly exceed 99 kph, but apparently there are enough of them that several manufacturers of bicycle computers will actually include a third digit in their displays. Sigma computers are known to work well on motorcycles, and so I found a Sigma BC-509 bicycle computer on Ebay for $7 shipped.
I needed the following features to make it work as a complete replacement for my cable speedo:
- three digit readout (100+ kph)
- odometer function (for maintenance intervals)
- tripmeter function (acts as a fuel gauge for most motorcyclists)
Pulling out the old speedometer was fairly easy. With the front cover off, only two bolts on the back and the speedo cable need to be removed. The other end of the cable was unscrewed from speedo drive on the front wheel, and a small plug in its place keeps the dirt out of the speedo drive gear.
On to mounting the bicycle computer. The computer itself would live in the familiar speedometer location. For this I cut out an aluminum plate to fill in the space and to hold the speedo. It took some trial and error trimming to get it to fit properly.
I had planned on using two-sided tape to secure the plate in place, but it held itself in place quite well with friction. The speedo itself is simply screwed on to this plate.
Note the grommet to keep the sharp plate from severing the wire.
With the cover in place, it was bvious that the shiny aluminum needed some black paint.
A few coats of paint and a few days later…
…the silver square still stands out against the black circles, but less so with a black background.
The other half of the speedometer is the pickup cable. This is normally tied to a bicycle fork leg with an elastic band, but this wouldn’t work on a bike due to the larger fork diameter and the greater forces involved with hitting potholes at 60+kph.
I carefully drilled two holes in the sensor and threaded through some black zip ties:
This could now be attached to the fork leg.
The sensor is triggered by a magnetic pulse, but the magnet included with the speedometer is designed for bicycle spokes and won’t work here. I first tried a random old magnet I had laying around but it proved too weak to trigger the speedometer sensor. A pair of old headphones gave up their tiny-but-powerful magnets instead, mounted to the front brake disc carrier. A little glue is extra insurance, but the magnetic force does a pretty good job holding the magnets in place.
For most motorcycles the cable attached to the computer isn’t quite long enough to reach down the fork leg, but with my little Ascot it was the perfect length. I made sure to have the forks completely unloaded before installing the cable. Otherwise, the cable might break when the forks extend to their full length. With a little more cable length I probably could have hidden the wire better (or run it along the brake line), but it’s not terribly hideous.
Once everything is installed the computer needs to be set up. I needed to program the time, total odometer reading (34,000km on this bike!), and wheel circumference. This is done according to the amazingly multi-lingual instruction booklet. Note that it’s not a speedometer, it’s a Funkclok. I think I’m okay with that.
I measured the circumference with a string around the tire, and came up with 1970mm:
A quick test ride showed me what it was like to know my speed while riding my Ascot. I no longer have to guesstimate my speed at Calgary’s many speed cameras! The only downside to this model is that it has a fairly slow refresh rate - it only updates the speed readout every couple of seconds. No biggie - it’s still way better than trying to guess your speed based on the traffic around you.
Cost:
$7 - Sigma bicycle computer
Incidental supplies:
magnets from old headphones
zipties
aluminum
grommet
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