Crawlpedia - 4x4 Calculators for Tyre Size, Gear Ratio, RPM

If you are looking for numbers these calculators on crawlpedia.com could come handy for you. :)

http://www.crawlpedia.com/calculators.htm

Metric / Inch Tire Size Converter
Enter your tire size information into one side of the tire size converter below to convert metric tire sizes to inches or inch tire sizes to their metric equivalents.

Ring and Pinion Gear Finder
Enter your original tire size and gear ratio into the form below along with your new tire size to find your recommended ring and pinion gear ratio.

Gear Ratio Calculator
Enter the number of teeth found on your ring gear as well as your pinion gear in the boxes below to calculate their combined ring and pinion gear ratio.

Crawl Ratio Calculator
Enter your transmission, transfer case, and axle gear ratios into the left side of the form below and press the calculate button to find your final crawl ratio.

Engine RPM Calculator
Enter your axle gear ratio, tire diameter, vehicle speed, and transmission gear ratio in the blue fields and click the calculate button to find your engine RPM.