fender extension: what a difference an inch makes!

[handlebar]

More than a year ago, I got a Bolton controller for my Radrunner. I rode every day and it worked until one recent morning, when sometimes the PAS wouldn't switch off or wouldn't switch on. The day before, I'd ridden on pavement after it rained. I figured water had gotten into the controller. My  $100 Radpower fender is pretty useless because it stops 11" off the ground. Any water thrown off the tire at that point will be rising with a velocity equal to the forward velocity of the bike.

I found crusty sand on top of the controller, which meant it had landed wet. The front cover had a grommet. I found a dirt trail where dirty water had run along a cable through the grommet. I left both ends open for three hours for the controller to dry. After screwing them back on, I used RTV to seal the seams on three sides. I didn't put RTV over the bottom seam because I thought the water hadn't come up from the bottom.

Next, I used 1mm polypropylene, sold as cutting boards, to make a fender extension down to 5.5 inches from the ground. To reduce the possibility that it would strike an object, I used a heat gun to bend it close the the tire. I wasn't able to test the fender until the next time I rode on wet pavement. The bottom of the bicycle frame got wet. That was a bad sign because it's 2" above the bottom of the controller.

I thought the RTV had protected the controller until the next morning, when I had trouble switching the PAS on or off. I left the ends off for an hour, blowing compressed air through it three times. This time, I sealed the end plates on four sides. I also made a fender extension extending to 4.5" off the ground. I bent it pretty close to the tire, so it probably won't hit anything. If it does, it will probably flex because it's attached only where the fender brace screws to the fender.

The next day I had more trouble with the controller. This time, I noticed at least once when everything worked but the speedometer. That happened at least once when the controller was new, so I guess it picked up moisture then, too. Now to dry it better, I opened it up and warmed the inside with a heat gun three times in two hours.

Later, there was a thunderstorm. Afterward, I tested the extension by taping on a cardboard shield to the frame. It was 6" behind the fender extension and 6" ahead of the controller. Besides wet pavement, I rode through puddles and along rivulets. I was limited to 15 mph. If I went faster, the cardboard would blow out of position.

The fender extension protected the cardboard down to a point 5" off the pavement. The bottom of the controller is 8.5" off the pavement, so it hadn't been wet through the gap in the cardboard. I wouldn't have thought one inch could make such a difference. Apparently it catches water from the tire down to a point where its vertical velocity is only 1/12th the bike's forward velocity.

[handlebar]

I tested the extension by taping on a cardboard shield to the frame. It was 6" behind the fender extension and 6" ahead of the controller. Besides wet pavement, I rode through puddles and along rivulets. I was limited to 15 mph. If I went faster, the cardboard would blow out of position.

The fender extension protected the cardboard down to a point 5" off the pavement. The bottom of the controller is 8.5" off the pavement, so it hadn't been wet through the gap in the cardboard. I wouldn't have thought one inch could make such a difference. Apparently it catches water from the tire down to a point where its vertical velocity is only 1/12th the bike's forward velocity.

It rained again today, and I tested my extension without the cardboard, riding two miles on wet pavement. Riding along a rivulet without the visual obstruction of the cardboard, I could see that the water drops that made it past the bottom of the extension didn't seem to rise above that level.

When I got back, the bottom of the frame was dry, but the bottom of the controller was wet, as was the bottom quarter inch of the front plate. I had to think about it. It was about 4" higher than the drops I'd observed today and the wetness that hit the cardboard yesterday. The controller must have been hit by droplets so small that I didn't see them, and so small that they were carried on air currents.

The fender extension helps to protect the controller, the chain, and my feet, but RTV is still worthwhile.