Tandem Cycling - Cateye CD300DW - Cadence Magnet Hitting Timing Chain - causes and fixes

In a recent thread inquiring about computers for the stoker, the conversation turned to the cadence magnet for the Cateye CD300DW (double wireless) making a click each time the magnet on the crank arm passed by the timing chain. When we first put on our CD300 a couple of years ago, we had the same problem

If the timing chain is loose enough, that will certainly allow the magnet to pull the chain over. Even if the timing chain is tensioned properly, if the magnet is positioned too far towards the end of the crankarm, then the magnet can pull the timing chain over.

I recommend positioning the cadence magnet very close to the timing chainring. This requires moving the sensor unit farther forward which then requires positioning the speed sensor magnet very close to the nipple end of the spoke. I currently have fenders on our tandem and the sender unit has to be tilted over a little bit because of the fender being in the way. I could sand / grind off some of the fender if I wanted it to stand perfectly upright.

Below are some photos. I hope this helps someone.

Santana Niobium
Bloomington, IN

We tried a VDO rear wheel / rear crank mount. Had many problems with magnet/pickup clearence. With the VDO I also found that the crank magnet was housed in a plastic housing zip-tied to the crank arm. Each revolution of the crank would cause the magnet to shift back & forth in it's housing (when it passed either the sensor or the chain stay - don't recall) and made a click each time. Very annoying. We never had any luck with the VDO. It also would often loose communication with one or both of the sensors. We switched over to a Garmin GPS. Much simpler & more reliable.

Kudo's BC for the tips and pics....


We switched over to a Garmin GPS. Much simpler & more reliable.

:thumb:

We tried a VDO rear wheel / rear crank mount. Had many problems with magnet/pickup clearence. With the VDO I also found that the crank magnet was housed in a plastic housing zip-tied to the crank arm. Each revolution of the crank would cause the magnet to shift back & forth in it's housing (when it passed either the sensor or the chain stay - don't recall) and made a click each time. Very annoying. We never had any luck with the VDO. It also would often loose communication with one or both of the sensors. We switched over to a Garmin GPS. Much simpler & more reliable.

I've used the VDO units I just used 3m double sided foam tape to stick it to the inside of the crank arm and also used a small magnet out of one of those refrigerator things and worked great. I also use a garmin gps on my other bike and have to say they are nice.

I am one of those guys who took off the cadence sensor due the chain deflection issue. I will try re-positioning the magnet and sensor this weekend and give it another shot. Thanks BC.

It didn't take me long to consider that the best crankarm for mounting a cadence sensor is the captain's right crankarm--no chain at all. On two tandems I have Avocet 45TT computers for the stoker, with the sensor mounted to the bottom tube, conveniently close to the captain's right crankarm. On most tandems, the captain's seat tube provides a convenient run for the wire to follow to the stoker's stem, and thence to the stoker's handlebars.

It didn't take me long to consider that the best crankarm for mounting a cadence sensor is the captain's right crankarm--no chain at all. ...

Sounds like a great idea for your Avocet but not an option on the Cateye CD300. The sensor / sender unit is "left-handed" and must sit on the left chainstay. The outside sensor arm is for the cadence magnet and the inside sensor arm is for the speed / distance magnet mounted on a spoke. The arms have a limited range of movement and can't be rotated enough to switch inside and outside positions. Since it's a wireless transmitter with a directional transmitter, I can't just mount it upside down on the right side chainstay - the transmitter would be aiming at the ground.

Attached is a image from the cateye website with a small image of the sensor unit below the larger image of the display unit that illustrates what I am trying to say.

Bloomington, IN

Thanks BC!

We had the same problem with our Garmin 305. I used one of those powerful magnets out of an old electric tooth brush. Had to re-tense the timing chin to prevent deflection. Next time I have to fiddle with it I will try to move it as far forward as possible.