I saw a picture of a guys singlespeed bike with vertical dropouts that used an old chainwheel or cog stuck in his chain near the rear dropout to achieve chain tension. Does anyone know if this works?

You mean something like this?
https://www.surlybikes.com/hotmetal/p...nglelator.html

These can't be used on fixed gears though.

nope it was just a chainwheel, nothing else and it was just suspended in the chain to take up slack.

It's called a ghost ring, I think Sheldon mentions it briefly on his site. Maybe I read it somewhere else but yea, it's rumored that it works if you have exactly the right ring and it won't hit the chainstays.

Wouldn't it pop off under bumpy conditions? Nifty idea.....I'll try one out just to see....

i heard it called a phantom gear. they do work somewhat, sometimes. the only problem is if they decide to stop working, expect mangled spokes. i tried it b4 but it doesnt work too well in bumpy conditions. luckily the gear stayed out of my back wheel when it fell out. i wouldnt do it.

I found out that 42-16 works on my bike perfectly!! I just got back from riding. I start work messengering tomorrow and i'll give a lil report after work in my other thread (messengering) Thanks for the help guys.