Friday, June 10, 2016

How To Not Do A Singlespeed Conversion


If you actually do want to do a single speed conversion, you need either one of two things: horizontal dropouts, or a chain tensioner. For fixed speed conversions, you can't even use a chain tensioner since the chain must accept tension in both directions for both pedaling and braking.  When I tried to make my bike a singlespeed, it was because my derailleurs and shifters were either breaking or broken at the time, and I figured I'd try singlespeed since I hadn't considered it as an option yet.  I had neither horizontal dropouts or a tensioner, this is what happened:

Vertical dropouts don't allow you to move the rear hub back and forth, which means you can only get the chain to fit on at certain gear ratios for the fixed distance you got. (unless you have a chain tensioner)  I had this setup with the chain strung on the cassette for whichever gear worked.  The problem is that chains eventually stretch, and even a slight amount of slack can mess things up.  With this setup, I inevitably had the chain falling off the rear sprocket and onto a smaller one.

It also doesn't help that the cassette sprockets are designed so that the chain can fall off easily (for shifting)
I wasn't convinced, so I decided to prevent the chain from falling off by sandwiching my sprocket between two bigger ones.  I first machined a spacer for the cassette hub.
Then placing it on the hub:
Then the gear sandwich:
I will say this, it was every bit as much of a failure as before, except this time with the added danger of getting the chain stuck on one of the larger sprockets (which it did just about every time I used it) and lock up the crank since the chain wasn't long enough to encircle the bigger sprocket.  It did, however, eliminate the chain falling off problem, which allowed me to actually ride it.  I just had to ride very carefully, pressing very lightly on the crank, almost to the point that it was just the weight of my foot doing the work, and if it did get locked up, jut pedal backwards a quarter turn to get it back in the middle.  As much as I'd like to say I could make this drivetrain work singlespeed, I'd rather not.  If you're bike's designed for gears, why not use them? That 22 mile ride with this setup was actually very enjoyable, I was in the middle of a 40 day fast, so it's not like I was in any condition to be pedaling very hard at the time. I remember listening to Earth Wind and Fire's "Fall in Love With Me" on my cassette player and actually really feeling the magic! And then at the end I went to the library and found a 5th Dimension record to end a fantastic day!
And then I found a Shimano Saint shifter and derailleur in the trash, and all my problems were fixed!

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