gear calculator?

[Jackasic]

trying to figure out how much a smaller tire will changes the gearing on our lemons truck. found this one, any idea how that would reflect in a gear change?

http://www.miata.net/garage/tirecalc.html

stock tires are 195/75-14's

[DRAGOONRANCH]

http://www.4lo.com/calc/geartire.htm

[DRAGOONRANCH]

195 / 25.4 * 0.75 * 2 + 14 is how you calculate it if you weren't sure.

25.5" Diameter

[bburris]

On a similar note, does anyone know of a more offroad vehicle friendly calculator that spits out RPMs at different increments like this one:
http://www.car-videos.net/tools/speedrpm.asp

That one works, but converting 42" tires makes me think I'm screwing something up.

[Fredo]

http://www.grimmjeeper.com/gears.html