1)   Off The Road Winch Load Calculator 1 OTR Trading has made this winch load calculator available to you for you to work out the load that a 4x4 winch would take based on the parameters you feed it. You can use this 4x4 winch load calculator on an electric or hydraulic winch scenario. 2)   Off The Road Metric Tire Size Calculator 1 As any 4x4 or car enthusiast should know, when you are dealing with formulas dealing with gear ratios and such - you will need to know the tire diameter in inches; this calculator will offer just that.