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Frequently Asked Questions about Cycling Computers

1. How do I determine wheel factor?

There are no standard wheel sizes in the cycling world - i.e. the circumference of a 700x23 tire will differ from one brand of tire to another. Read the following to better understand why you should do a wheel roll-out test to determine wheel factor: http://www.sheldonbrown.com/tire-sizing.html .

The best way to determine wheel factor (i.e. wheel circumference c) is to do a wheel roll-out test:

1. Inflate you tires to its proper pressure.
2. Put a mark on your front wheel on the outside circumference.
3. Put a mark on the floor.
4. Put the mark on the wheel on the mark on the floor.
5. Rotate the wheel one full revolution until the mark on the wheel is on the floor again.
6. Measure the distance between the marks in mm. This is the wheel factor.

To convert inches to mm go to www.google.com and type in '88 in to mm' (or whatever value in inches you measured the circumference of your wheel to be) and it will covert inches to mm for you.

See www.filzer.com/img/products/wheelfactor.wmv for short video on how to determine wheel factor.

For a rough estimate of wheel factor you can use the values below:

For more sizing information see  http://www.sheldonbrown.com/cyclecomputer-calibration.html.

2. Does it matter where I put the magnet on the wheel?

Nope! The computer counts revolutions of the wheel and regardless of where you put it the magnet will pass the sensor once every revolution.

So magnet placement is not important. However we do recommend that you put the magnet near the center of the spoke (i.e. midway between hub and rim) - while at the same time making sure the sensor is in a secure/stable location on the fork.

3. How does the computer measure distance and velocity?

Since you enter the wheel factor (i.e. circumference) into the computer:

Distance = number of revolutions x wheel circumference
Velocity = revolutions/minute x wheel circumference

4. What if I am not getting a signal from the transmitter?

a) Wireless units

If you have a dB4LW or a dB4LW-C (wireless speed sensor only) and are not getting a signal from the speed transmitter:

• If the screen is blank, check the computer battery and replace if necessary.
• Check the battery in the transmitter and replace it if necessary.
• If you are still not getting a reading, pass a large fridge magnet back and forth over the circle arrow on the transmitter and bring the computer near the transmitter.
• If you do get a reading then the wheel magnet and transmitter are likely misaligned.
• Still no reading? There is something wrong with the transmitter or computer.  

b) Wired units

If you have the dB2L or a dB4LW-C (wired cadence sensor only) wired version of the bike computer and are not getting a speed (or cadence) reading:

• If the screen is blank, check the computer battery and replace if necessary.
• Make sure the computer is properly locked into the handlebar mount.
• If you are still not getting a reading, pass a large fridge magnet back and forth by the sensor and see if you get reading.
• If you do get a reading then the wheel magnet and transmitter are likely misaligned.
• Still no reading? There is something wrong with the wiring harness or computer.  

5. Why am I getting weird readings on wireless computer units?

Electronic interference is usually the cause of erratic reading on the computer unit especially when this happens and you are not moving.

Possible sources of electronic interference include cell phones, flashing LED lights, alarm systems, high voltage wires, computers, florescent lights, car electronics, MP3 players, etc...

If you move the unit away from the interference the erratic reading should stop.

6. Instructions

• dB2L
• dB4L
• dB4LW
• dB4LW-C
• dZ2L
• dZ4L
• dZ4L-C
• dZ4LW
• dZ4LW2

7. Videos
For the dZ computers there are videos showing how to install the computer on a bicycle located on the computers main web page.