Bike computer won't work
 

Okay, I followed the instruction manual for my new computer, the batteries are brand new and yet my bike computer won't work. What gives, any help, or do I need to be more specific...

Return it..................If you are sure everything is OK on your installation...........

Well it turns on, but the instructions were so vague that they're like, wrap the wire around the brake wire down the fork, loosely but not too loosely that it interferes with your tire or braking mechanism, and then it has a picture of where to place the sensor, I put it there, put the magnet on the wheel like the picture shows, and squat, did I do something wrong, the instructions stopped there.

Make sure the magnet is close enough to the sensor, also be careful when using zip ties to secure wire that you don't tighten the too tight, you can break the wires inside.

What kind of computer is it?

Make sure that the magnet lines up with the proper markings of the sensor. Some have one line that it should match up with and others have two lines that it needs to be between. Also make sure it is close enough.

what they said...plus a bit.

Not knowing what computer your using, I'll tell about mine. They are both Sigmas. In the manual, the picture shows the magnet and pick up sensor at the edge of the rim. It won't work there, I tried. My LBS recommended I mount both closer to the hub. You want, at most, about two pennies thickness distance between pickup/sensor. And the wires are delicate as stated.

Both computers work now and are fairly accurate.

I think in the manuals they say how far apart they need to be in MM's. I had the same problem with a wireless sensor, until I made the spacing half of what they said they needed and then it worked fine. I have all of mine about 2/3 of the way to the outside of the rim and they work just fine. It might just be the spacing that is wrong, of course unless you damaged the wires.

To test it, take the magnet off of the rim, and move the magnet rapidly across the sensor and see if your computer shows that it works or not. I did that with the wireless setup for my wife's bike, so I knew it wasn't a computer problem and that the sensor wasn't close enough.

Defiantly magnet/sensor alignment. Usually you need to put the sensor 1-3mm from the magnet and have the magnet pass at the sensor line.

Ah thanks for your help everyone! I'll be sure to check next time I go out for a ride *tomorrow*. :)

Yep. The magnet needs to be pretty close to the sensor. When I transferred mine over to my new bike it didn't work. I had to place a cardboard shim under the sensor to place it closer to the spokes.

Good luck!

You can do it today before you go for your ride. As flip18436572 says, the magnet needs to be close to the switch. They need to be almost close enough to touch. The magnet and sensor should usually be close to the hub because that's where the wheel is it's widest.

Put the bike in a rack or hang it from the rafters or get someone to hold it up for you. Slip the sensor around until the sensor and magnet are just about to touch. Spin the wheel and watch the computer. If you are close enough, you'll get a reading. If you don't, slip the sensor a little closer until something happens. Once you got the sensor in the proper place, use a permanent maker to clock the position and tighten up the sensor.

If none of this works, you may have to play with the angle of the sensor to align it with the magnet.

To expand on cyccommute's good advice, the sensor does not have to be between the fork and the spokes. It can sit in front of, or behind, the fork blade.

I always make sure it's in front of the fork blade. This way, if it accidentally makes contact with the magnet it's not going to be forced between the wheel and the fork.

Thanks for the advice everyone! I got it to work right, and I clocked myself at 30+ miles per hour on one of the down hills today! I didn't even know I was going that fast, I thought before I had the computer working, that maybe I was going 15-20 maybe 25, I was surprised to see that number. :)

Make sure you have it set on mph (miles per hour)and no KMph (kilometers per hour).. Plus if the sensor is a lil too far, it can give you bogus readings. I once returned from a ride where my 'puter said my max speed was 99. 5 mph!:D

Computers need to be set up with the right wheel diameter, they can provide really bogus readings if they are not.

Most computers are set for the circumference of the wheel in millimeters, the best way to determine this is quite simple. Get a metre stick (a yard stick that is 1 metre long) and a piece of sidewalk chalk, now:

1) on a sidewalk or road mark off 10 metres,
2) pump your tires to the normal pressure you use,
3) put the wheel on the first mark, with the valve stem at the mark.
4) Now ride along your 10m route, counting the number of complete revolutions
5) if your valve stem isn't at the bottom, move forward until it is.
6) measure the distance from your 10m mark to where your valve stem lies.

Now comes some math....

Say your total distance is 10m 23 cm and you made 5 revolutions multiple m by 100 add centimetres then multiply the total by 10 to get millimetres, divide by 5 and you get 2046 this is the number you put into the computer.

Obviously to do this properly you need an assistant, who will do the extra measuring and the counting of revolutions. If you measure it, you can get very good accuracy, something like 1 yard within 600 miles, that's close enough. If you change tire sizes or lose/gain a lot of weight this can affect the measurement, so you may want to repeat it once in a while.

Okay when I said I didn't know I was going that fast, I have no sense of speed other than what you feel when you're behind the wheel in a car. My mom and I sat down when we were visiting the other day and figured it out, so I know it's right right now. I'll be sure to re check every 10 pounds or so to make sure its accurate. :)