4WD.ai

Free tools

4x4 calculators

Five calculators that know your truck. Compare tire sizes, fix the speedometer, check wheel offset, pick gears for bigger tires and check a trailer against your ratings, starting from the maker’s own numbers for 6,226 configurations.

Tire size calculatorCompare two sizes side by side: diameter, width, sidewall, revs per mile, speedometer, ground clearance and gearing, drawn to scale.265/70R17 → 285/75R17: +2.2 in, +1.1 in clearance
  • How much taller is 285/75R17 than 265/70R17?
  • What is a 33-inch tire in metric?
  • How much clearance do bigger tires add?
OpenSpeedometer calculatorWhat the speedometer shows at 25, 45, 60 and 75 mph after bigger tires or a regear, and how far off it is.On 285/75R17s set for 265/70R17: 56.1 mph at a true 60
  • How fast am I really going on bigger tires?
  • Does a regear fix the speedometer?
  • When should I recalibrate?
OpenWheel offset calculatorHow far a new wheel and tire stick out, how much room you gain or lose inside, and the backspacing, drawn to scale.17x7.5 +30 → 17x8.5 0: face +1.7 in, backspacing 4.75 in
  • How much will a 0 mm offset wheel poke?
  • What backspacing is a +30 mm offset?
  • Will a wider wheel hit the suspension?
OpenGear ratio calculatorEngine rpm at highway speed from tire size, axle and transmission ratio, and the axle ratio that gives bigger tires the stock gearing back.3.583 on 285/75R17: acts like 3.35, 1,506 rpm at 65; 3.91 restores it
  • What gears do I need for 35s?
  • What rpm will I cruise at?
  • Is 4.10 or 4.56 right for my tires?
OpenTowing calculatorA trailer, its tongue weight and what is in the truck, checked against max towing, payload, GVWR, GCWR and the tongue rating.Trailer + tongue + people + cargo against max towing, payload, GVWR, GCWR
  • Can my truck tow this trailer loaded?
  • How much payload does tongue weight use?
  • Am I over GVWR or GCWR?
OpenRig builderNot a calculator: your truck drawn to scale. Add a lift, tires and gear, and watch clearance, angles and payload change.Build my rig

For my vehicle

Your truck’s numbers, not a guess

Pick a make, model and configuration in any calculator and it starts from that configuration’s stock tire, axle ratio, gears, wheel offset or towing ratings, each from the maker’s own document and linked to it.

configurations with a stock tire size
6,226
with an axle ratio
4,293
with the transmission’s gears
5,365
with a published wheel offset
1,770
with towing and weight ratings
10,251

Makermarks a number from the maker’s document. A rating the maker doesn’t publish for your configuration is shown as not published, never filled in.

Everything a calculator works out is math on those numbers and on what you type, labelled as such, with its formula on the page. It’s guidance, not engineering advice.

Questions

Which tool, and how far to trust it

Which calculator do I need?

Going to bigger tires: the tire size calculator for height, width, clearance and speedometer (it starts from the stock size of 6,226 configurations), then the gear ratio calculator for the axle ratio that brings the gearing back (5,365 configurations with their gears).

Speedometer reads wrong after new tires: the speedometer calculator, which knows the axle ratio of 4,293 configurations.

New wheels: the wheel offset calculator for how far the tire moves out or in (published offsets for 1,770 configurations).

A trailer: the towing calculator, which puts trailer, tongue weight, people and cargo against the towing, payload, GVWR and GCWR ratings of 10,251 configurations.

How accurate are the results?

The maker’s numbers are as printed, each linked to its document. Tire math runs on the size code: a real tire measures within about 1.5% of it, by brand, tread, wheel width and pressure, so heights and speedometer figures carry that range.

Towing checks use the maker’s ratings for the configuration you pick and the weights you type in; they aren’t a weighbridge. Your truck’s own GVWR and axle ratings are on its door label, and a scale tells you what the loaded rig weighs.

Do the calculators know my truck?

If it’s one of the 84 models we cover: pick the make, model and configuration and the calculator fills in what the maker publishes for it. Where a figure isn’t in the documents we hold, the calculator says so and you type it in; nothing is guessed.