Magic Gear Dilemma and Safety Concerns
OK, I have a single speed that I built up a while back on a spare road frame I had (with vertical dropouts). I was using a 9-speed freehub rear wheel and an old 17 tooth cog that I lined up with spacers for a good chainline. I was also using a Surly Singleator for chain tension. Keep in mind that I am not riding fixed, just single speed.
Well yesterday I got thinking that I'd like to ditch the tensioner for a cleaner look, so I started thinking about the magic gear and trying to get that work. First I figured I might be better off getting a few BMX cogs (for taller teeth) just to minimize the risk of chain slippage.
Well to make a long story short, I ended up getting it to work (I think) with the 45 tooth chainring I was using and a new 17 tooth BMX cog. I have some concerns, though: my chain is tight enough such that when pedaling in the workstand, I can feel some slight grinding, and the crankset barely wants to bind at a couple spots. Yet, when I check the play in the chain my pushing it up and down, there's slightly more than the 1/2" of movement that I have read to be optimal. I'd say it's about 3/4" total vertical change. So how can it be that my chain is looser than recommended when checking the play, but too tight to cause a little resistance?
Also, according to the online magic gear calculator, this combination shouldn't work for my frame, if the frame maker's chainstay spec of 41cm is accurate. Also of note is that with my old 17t cog from an old cassette, the chain was way too loose, but it's tighter with a new cog. Could the old cog have been that worn?
So I just want to make sure that I'm ok on safety with this setup. Also, I assume I'm ok using a regular 9-speed chain with a couple Powerlinks to get the length right.
Thanks, sorry for the long-windedness.