Hey Science Guys: A Coker Conundrum

I recently installed a Schwinn computer on my standard Coker. At first, I had to use both of the pads under the sensor in order to get the sensor and magnet close enough together to “read”. The problem came when I’d “power forward” or do any level of hill climbing. As soon as I’d start pulling on the seat and having to really push hard on the pedals, the magnet would start hitting the sensor each time around.

I removed one of the pads–making the gap bigger–and the problem seemed to go away. The computer still functioned, and the collisions stopped. At least until I rode up a really steep hill. Then they started again.

Gauss, Childs, Harper, Smart Guys: what’s happening here? Why should the distance between my spokes and my frame be shrinking when I climb hills? Are my spokes just too loose? I’ve never seen anyone write about this particular phenomenon…

When you’re pulling hard on the handle, and pushing on a pedal, there’s a big twisting force (moment) through the frame. pushing on the left pedal and puling with the right hand for example will twist the top of the frame clockwise looking from above. This will make the ‘spoke to frame’ gap open and close as you pedal.
The easiest way to solve this should be put the magnet on a spoke next to a crank arm, as when this is against the sensor on the fork leg, the pedals will be at 6 and 12 o’clock, so there should be very little force being tramsmitted throught them, and so very little twist…

This makes total sense. I just went out to look at my setup…I think your advice is right on, and I’ll test it tomorrow and report back. I have my magnet set up “left facing”, and it’s position is such that it’s aligned with the sensor when my left pedal is between 7 and 8 0’clock, a point of maximum downward force.

Aligning with the crank seems like a good solution. In my dreams, having a more rigid Hunter 36 frame and the beefy rim and hub setup would be another…

Thanks for the tip Joemc. Will try it and get back to you.


So for the record, my hasty overuse of the apostrophe was out of exhaustion, not ignorance. I hate it when my pet peeves roost so close to home.

Moving the magnet and sensor further in towards the hub will also help, but after joemcs suggestion you probably won’t need to do that.

I had problems with the Coker wheel rubbing against the brake on hard torques, like climbing a hill and idling, even with the Strongest Wheel setup. It wasn’t until I raised the average spoke tension another 60% did the problem go away.

My conclusion was that wheel flex was the primary problem and that only with the proper bracing angle (i.e., wide hub) and a very high spoke tension does the 36" wheel stiffen up. These elements are not obtainable with standard components and standard wheel building practices.

this thread.

The magnet placement idea is amazingly creative and insightful.

The suggested fixes offered by our fellow posters may do the job but, you know the real solution :smiley:


In addition to being creative and insightful, it was successful. I moved it this afternoon to align closely with the left crank. Did an 8 miler tonight with several significant hills requiring lots of torque. No hits at all… :slight_smile:

Thanks for the tip Joemc. From now on when I sent out a “calling all smart guys” message asking for help, I’ll know you’re a member of that club.


You’ll notice that I kept silent on this thread. I hope I’m not out of your exclusive club. :slight_smile:

No way…you can’t leave the club! It’s just good to know there are some quality backups available for when “Ask John” takes a vacation. :sunglasses:

cowers in shame

Hey!! No reason to cower U-Turn…I would not have even been in the situation to be able to ask the magnet question were it not for the great advice from you and others around the “Miyata/GB/Seat” re-build. You got me through that process, which gave me someplace to mount the computer, which then led to the magnet issue.

You see, I prefer to create my problems in a linear fashion, so am grateful that there always seems to be someone (often many) willing to help me out when I step in it… :sunglasses:

Cheers, TB