Lots of handy stuff here for techheads and wannabes like me,i like the tire size calculator,now i know why some people recommend 195/65/15 or 205/65/15 if you can squeeze them in,doesnt change your speedo as much as others,anyway have a look go on you know yule need it one day, http://www.csgnetwork.com/automotiveconverters.html 

Other good programs are found here
http://www.bgsoflex.com/auto.html

And I have made a few, the most complete being my excel dyno which will do all your tyre size calcs, gear ratio calcs, and of course acceleration calcs. Only prob is you need excel
http://offroadvw.net/tech/calc.htm

and I also have an engine size calc
http://offroadvw.net/tech/wes/capacity.htm (easy calc for me to start learning html based calcs.)