Well I know theoretically why, sort of. It wraps around the brake wire and then goes all the way down to the thing holding the wheel in place. And I fiddle with all those things when I remove the wheel.
What I don’t know is why, every time I remove it, the computer no longer “hooks” up to the bike? And how do I get it back to work? The So’s not here and I’m ashamed to admit that I pretty much let him hook up the computer. Ashamed because everything else on the bike I’m learning to do myself.
How do I hook it back up, or better yet, make it stay connected? If this is vague, I’m sorry. Basically, when I remove the wheel and put it back on, it no longer counts my miles or anything.
I’m not sure what you mean by “every time you take the wheel off.” Does it start working again on its own?
Your problem sounds like the sensor is not being actuated. Most cyclecomputers use a magnet mounted on the wheel to actuate the sensor. Is it still aligned with the sensor, and on the side of the wheel next to the sensor? It could be that you are putting the wheel on reversed from the original orientation, and the magnet is now on the opposite side.
No, I know I am putting the wheel on the right way. See, I have those detachable wheels, so I can load the bike into the back of my car and take it places. This is at least every summer.
Ok, so it’s a magnet and a sensor? Let me go and try to see what it is. See, I didn’t even realize there was a magnet.
Ok, I found the magnet and the sensor, and they are indeed both on the same side. When I reattach the wheel, is there something else I have to do to activate it?
No, not usually. The sensor may have been moved a bit if you were not careful when removing the wheel. The magnet should pass by the sensor very closely when the wheel is rotating. The sensor is usually mounted in some flimsy way, so see if you can move it closer to the magnet, but not so close that they actually touch.
It looks lined up almost perfectly. And I’ve just spun the wheel several times, and tried to reset the computer. Nothing. It just keeps saying 0.00 on all the screens.
You should just have to plug it in and turn it on, though it could depend on the model. I would also check the connection at the computer, the batteries, and the integrity of the wire, as well as resetting the unit.
Also, does it start working if you flex the wire? Set the wheel spinning, then run your fingers along the length of the cable, gently bending it between your thumb and finger. If a measurement registers on the cyclecomputer, you have a faulty cable.
I can’t think of anything else other than making sure that the computer is fully clipped in to the holder. Generally, computers will stop updating if they don’t receive input from the measuring device (magnet and sensor) within about a second or so. All it needs to start again is for the sensor to send a signal.
It’s fairly unlikely that the sensor is damaged, as there’s not much in it to break (unless it gets caught in the spoke or something, and that’d be obvious) . It’s much more likely that it and the magnet are just not optimally aligned, or that the cable is broken.
Nothing! It doesn’t work if I flex the wire. I checked the connections, they all seem OK. The batteries are obviously working, since it does show numbers, and I can get it to start a timer…just starting at zero, and counting, not matching anything.
I tried to make sure the computer is fully seated. I even checked the touch points to make sure there was no dirt or filth on them. Shiny.
Thank you all for your help. Unless anyone can think of anything else, though, I may have to wait until Sunday.
Interesting. A couple of thoughts I had on my way back from buying some milk: Make sure the sensor is facing the right direction. It should have some indication as to which side is the wheel (magnet) side. If it is backwards, the magnet will pull the switch away from the contact rather than toward the contact.
Remove the sensor from the bike, then move the magnet to and from the sensor with your hand. Try a stronger magnet too. If it works it means there is some sort of alignment problem.
One other thing you can try is test the sensor directly. Using a multimeter or other continuity tester, connect the tester leads to the cable and put a magnet near the sensor. If the circuit is open with the magnet removed and closed with the magnet in place the sensor is working.
The magnet has to face the pickup and the distance between the magnet and the pickup is very important. If the magnet is just a touch too far away the system won’t work.
Try this:
Rotate the wheel until the magnet is as close as possible to the pickup. Hold the bike and get down on your knees and look closely at the gap between the magnet and pickup. IIRC the spec for most cycle computers I have delt with is about 1/4-5/16" (6-8mm). What I have found is that closer is way better.
Possible problems:
Because the spokes slant if the magnet has moved up the spoke slightly the effective clearance will be too large, and no signal will be picked up. You want the top of the magnet to be about even with the top of the pickup, not way above it
If the magnet has turned slightly, again the magnetic field will be too weak. If you have a magnet like most there is a small black plastic piece that sticks off from the spoke, and a metal cap on the other side of the spoke. The black plastic part is the magnet. You want the that to pass as close as possible to the pickup.
If the pickup has rotated away from the spoke you will again wind up with too much clearance, and no speedo.
Try moving the pickup/magnet so that they just kiss as they pass one another. then increase the clearance till they just clear. Raise the wheel and spin.
If it is a pickup placement problem this should fix it.
Don’t feel bad, bike computers can be finicky things, and all of us have problems with them every so often.
