Ok, so you got a lift and slapped on bigger tires?! They look tough and could be very functional, but they could be robbing you of power/gas mileage. This calculator will help you find a gear ratio that make your rig perform close to stock specs.
Now that you got those new tires, your speedometer is off. Uses this simple ratio calculator to approximate your correct speed.
Crawl Ratio. The one number everyone wants to know. This is for bragging rights afterall. Only number more important than this is your checking account balance. You'll need to do a little research by finding out the transfer case and transmission ratios first.
Estamates your actual MPH. Knowing your gear ratios and tire size will get a more accurate result.
If you don't have a tachometer you could use this form, otherwise it's only useful to find out how accurate your Tach is.
Convert those metric tires that are common on just about everything stock to a number you can understand. For example a 265/75R16 would be around 31.6 inches tall.