For those using these, do you use the same size cogs on both?

What's the point with using two cogs of the same size? Then there is no reason to flip/flop it. Use a different size cog on the other side or a BMX freewheel for some variation...

With a flip flop, you could coast on one side, so concievably someone could want the same ratio. I think most people use a larger freewheel, because if they get to the point in the ride that they need to coast, then the easier gearing is a plus.

Usually when I hear cog, I don't think 'BMX freewheel", i think fixed cog...

I agree with you on the same sized BMX freewheel on the flop side...

That would be a fix/fix not a flip/flop. Semantics and terminology. Kind of like brakes/breaks. Both seem the same here...

unless you have horizontal track drop outs, chain length maybe an issue for you. If you cut your chain for 15t cog and it fits just perfectly it maybe too short on the freewheel side if you run a 16t.

Is there some sort of formula for figuring out how much more chain you will need for each increase in cog teeth? Just curious...

You can go out 50 miles fixed and if you feel a little bonked coming back, flip your wheel and ride the freewheel back home. Your freewheel can be a tooth or two larger than your fixed cog.

1 tooth increase on a cog/freewheel/chainring = about an 1/8" of chain length needed

does anyone actually flip their wheel? i just have those extra threads on the freewheel side hanging out, doing nothing. I might actually flip the wheel around just to see what it's like, but then I'd have to take off my lockring and cog, and put brakes on... so it's probably never going to get done unless I get snowed in and go insane.

i have a 17 on the freewheel side loctice on, then i have a 16 on the other side. just so i ll have a change every once in a while

if one sides cog was larger than the other, when you flip it would you have to add on to the chain?

Depends on the difference. It's why horizontal long dropouts are recommended.