Gear Ratio Calculator 4Lo: Formula, Worked Example & Low-Range Tables

Crawl ratio is the total gear reduction available in the lowest gear: first gear × low range × axle ratio, and it decides how slowly and how strongly a vehicle can move over an obstacle. A high crawl ratio lets the engine idle the vehicle forward at walking pace with a large torque multiplication at the wheels, which is what off-road driving needs when traction is poor and the surface is uneven. This page explains the formula, works through a complete example with stated numbers, and shows how changing the axle ratio or the transfer case changes the crawl ratio — with the reminder that every number here is an example to be replaced by the figures for the actual vehicle. That is the point this page works through for gear ratio calculator 4lo.

Taking gear ratio calculator 4lo as the case in point: The formula is crawl ratio = first-gear ratio × transfer-case low-range ratio × axle ratio, and because it multiplies three numbers, a small change in any one of them moves the result noticeably. A vehicle with a 4.46 first gear, a 2.72 low range and a 4.10 axle ratio has a crawl ratio of 49.7:1, meaning the engine turns almost fifty times for each wheel revolution in low range. The worked example below shows the arithmetic, the table shows how the crawl ratio changes with different axle ratios, and the rest of the page covers what a high crawl ratio does on the trail, what it costs on the road, and the mistakes people make when they chase a bigger number.

This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.

How the gear ratio formula works for gear ratio calculator 4lo

The arithmetic is straightforward once the four inputs are clear. RPM = (speed in mph × gearbox gear ratio × axle ratio × 336) ÷ tyre diameter in inches. The 336 folds together the 5,280 feet in a mile, the 12 inches in a foot and the 60 minutes in an hour, so it is a constant of the units rather than a property of the vehicle. If the gearbox is in a 1:1 gear, the gear ratio is 1.00 and the formula shortens to RPM = (speed × axle ratio × 336) ÷ tyre diameter. Rearranged, speed = (RPM × tyre diameter) ÷ (gear ratio × axle ratio × 336), which answers the opposite question: how fast is the vehicle going at a given engine speed. Every table in this article is built from those two formulas with the assumptions stated next to it, so any line can be re-checked. That is the point this page works through for gear ratio calculator 4lo.

What a gear ratio is for gear ratio calculator 4lo

On this page, gear ratio calculator 4lo is the case in point: The axle ratio is the final multiplication in the driveline. The engine's torque passes through the gearbox, where each gear multiplies it by its own ratio, then through the differential, where the ring and pinion multiply it once more. A 3.73 ratio multiplies the torque arriving at the differential by 3.73 before it reaches the wheels, while a 4.10 multiplies it by 4.10. That extra multiplication is why a numerically higher ratio feels stronger off the line and holds speed better on a grade with a trailer behind it. The trade is engine speed: at the same road speed and in the same gearbox gear, the higher ratio turns the engine faster, which is why cruising RPM rises when a shorter ratio is fitted. The ratio itself is set by the tooth counts of the ring gear and pinion, so it is a physical fact about the axle rather than a setting that can be adjusted from the driver's seat.

gear ratio calculator 4lo: Worked example: crawl ratio from first gear, low range and axle ratio

For gear ratio calculator 4lo, the point is this: Take a gearbox with a 4.46 first gear, a transfer case with a 2.72 low range, and a 4.10 axle ratio. The crawl ratio is 4.46 × 2.72 × 4.10 = 49.7:1, so the engine turns 49.7 times for each wheel revolution in first gear and low range. At an idle of 700 RPM the wheels turn at 700 ÷ 49.7 = 14.1 RPM, and with 33-inch tyres that is a road speed of about 1.4 mph — slow enough to pick a line over rocks without touching the brakes. Change only the axle ratio to 4.56 and the crawl ratio becomes 4.46 × 2.72 × 4.56 = 55.3:1; change the low range to 4.00 and it becomes 4.46 × 4.00 × 4.10 = 73.1:1. Each input multiplies, so the table below shows the crawl ratio for the common axle ratios with the same example first gear and low range.

Crawl ratio table: axle ratio compared for gear ratio calculator 4lo

Assumption: first gear 4.46 and low range 2.72 (examples — use the figures for the actual gearbox and transfer case). That is the point this page works through for gear ratio calculator 4lo.

Axle ratio Crawl ratio Wheel RPM at 700 engine RPM
3.73 45.2:1 15.5 RPM
4.10 49.7:1 14.1 RPM
4.56 55.3:1 12.7 RPM
4.88 59.2:1 11.8 RPM

On this page, gear ratio calculator 4lo is the case in point: The table shows why the axle ratio is the easiest crawl-ratio change to make and why it is also the bluntest: moving from 3.73 to 4.88 lifts the crawl ratio from 45.3:1 to 59.2:1 with the example gearbox and transfer case, a 31% increase in torque multiplication and a 31% drop in crawl speed. A lower transfer-case ratio — a 4.00 low range instead of 2.72 — moves the number further still, but it is a bigger job and a bigger expense. The right crawl ratio is the one that lets the vehicle move slowly enough for the terrain without the engine labouring, and it is judged on the trail rather than on the chart.

How tyre diameter changes the answer for gear ratio calculator 4lo

The tyre diameter belongs in the formula because it sets how far the vehicle moves per wheel revolution. A 35-inch tyre travels about 110 inches per turn while a 31-inch tyre travels about 97 inches, so the same driveshaft speed moves the bigger-tyre vehicle further and the engine turns more slowly at a given road speed. That is why a ratio that felt right on the original tyres can feel sluggish after a lift and bigger tyres: nothing about the engine changed, but the effective gearing grew taller by the same percentage as the diameter. The fix is a numerically higher ratio that brings the RPM back to where it was. All diameters quoted here are nominal new-tyre figures computed from the size code, and real tyres vary slightly by brand, model, wear and inflation pressure. That is the point this page works through for gear ratio calculator 4lo.

What the ratio does on the road for gear ratio calculator 4lo

Taking gear ratio calculator 4lo as the case in point: What a ratio change feels like depends on the direction. A shorter ratio — a higher number — raises engine speed at every road speed, sharpens throttle response, makes towing on grades easier and brings the engine into its power band sooner after each gearchange. The price is paid on the motorway: higher cruising RPM, more engine noise and, usually, more fuel used at a steady cruise. A taller ratio — a lower number — does the reverse: quieter, lower-RPM cruising and less fuel at steady speed, at the cost of lazier acceleration and more downshifting on hills or with a load. Neither direction is free, which is why the choice is a compromise between the vehicle's hardest job and its most common one, and why the tables below show the RPM for several ratios side by side instead of recommending one.

How to find the ratio already fitted for gear ratio calculator 4lo

For gear ratio calculator 4lo, the point is this: Before choosing a new ratio, establish the one already fitted. The differential cover often carries a stamped metal tag with the ratio, and the owner's manual and door-jamb placard record the factory specification. The VIN, decoded through the manufacturer or a parts catalogue, returns the same build information and is a good cross-check — but it cannot reveal an axle that a previous owner swapped, so it is not conclusive on its own. Counting teeth is conclusive: the ratio is the number of teeth on the ring gear divided by the number on the pinion, so a 41-tooth ring gear driven by an 11-tooth pinion is 41 ÷ 11 = 3.73. Do that check before ordering parts, because every calculation on this page starts from the ratio actually in the axle, not the one the paperwork says should be there.

gear ratio calculator 4lo: Common mistakes with gear ratios

For gear ratio calculator 4lo, the point is this: The most common mistake is changing the ratio without checking the tyre diameter, or changing the tyres without checking the ratio — the two are one calculation, and doing half of it leaves the gearing wrong in the other direction. The second is comparing ratios across vehicles with different tyre sizes: a 3.73 on 35-inch tyres is effectively taller gearing than a 3.73 on 31-inch tyres, so the number alone does not describe the driving experience. The third is forgetting the gearbox: the formula needs the gear ratio of the gear in use, and overdrive gears below 1.00 change the answer, so a table built for top gear does not apply in third. The fourth is treating a calculated RPM as a promise about fuel use — RPM is one input to consumption, not the whole story, and load, aerodynamics and driving style move the result. And the fifth is assuming a ratio change is a fitment approval: it is a calculation, and clearances, load ratings and the placard still need checking with a professional.

Related pages for gear ratio calculator 4lo

Frequently asked questions

How do I calculate crawl ratio?

For gear ratio calculator 4lo, the point is this: Multiply the first-gear ratio by the transfer-case low-range ratio by the axle ratio. For example, 4.46 × 2.72 × 4.10 = 49.7:1. Use the figures for the actual gearbox, transfer case and axle — the example numbers on this page are illustrations, not the figures for any particular vehicle.

What is a good crawl ratio for off-roading?

Taking gear ratio calculator 4lo as the case in point: There is no single right number: it depends on the terrain, the tyre size and the engine. A crawl ratio around 50:1 suits general trail driving, while dedicated rock crawling often uses 70:1 or more. Higher is slower and stronger at the wheels, but it also means more drivetrain parts to maintain. Judge it by whether the vehicle can move slowly enough for the terrain without riding the clutch or the brakes.

Does crawl ratio matter in 4Hi?

Taking gear ratio calculator 4lo as the case in point: In 4Hi the transfer case is in high range, usually 1.00, so the crawl ratio is just first gear × axle ratio — much lower than in low range. Low range is where the crawl ratio matters, because the transfer case multiplies the reduction. That is why low range exists: it gives the slow, high-torque movement that high range cannot.

Does changing the gear ratio affect the speedometer?

On this page, gear ratio calculator 4lo is the case in point: Yes, indirectly: the speedometer is calibrated for a rolling circumference, and a ratio change does not change the tyre, so the speedometer reading itself is unaffected by the ratio alone. What changes is the engine speed at a given road speed. A tyre-size change does affect the speedometer, because it changes the rolling circumference — see the speedometer error calculator for that calculation.

Can I change my gear ratio myself?

On this page, gear ratio calculator 4lo is the case in point: A ratio change means replacing the ring gear and pinion and setting the backlash and preload precisely, which is a specialist drivetrain job with special tools. An incorrect setup fails quickly and expensively. Most owners have the work done by a drivetrain specialist, who can also confirm the ratio suits the axle, the gearbox and the way the vehicle is used.