My favourite gear calculator, Rabbit, is STILL not working
Please don't tell me they've killed it.

Here's the old link: http://software.bareknucklebrigade.c...it.applet.html
The thing I really found useful was it gave your cadence for various speeds. On flat ground, this isn't a great deal of use, but in hilly countryside, it give some idea of what you'd be facing. Nothing beats bolting the cog to the bike and trying it of course but ...