What Is 3.31 Gear Ratio: RPM, Speed & What 3.31 Means on the Road

A 3.31 gear ratio means the driveshaft turns 3.31 times for every single turn of the wheels, and that one number sets the engine speed at every road speed. In top gear, where the gearbox ratio is 1.00, the engine speed follows directly from the ratio and the tyre diameter: a 3.31 ratio on 205/55R16 tyres (631.9 mm, 24.88 in) puts the engine at a very specific RPM at 30, 50 and 70 mph, and this page works those numbers out line by line so the result can be checked by hand. The tables below use the formula RPM = (speed × gear ratio × final drive × 336) ÷ tyre diameter in inches, with the assumptions stated next to each table, and the rest of the page explains what the ratio does to acceleration, cruising, towing and fuel use — and what it does not do. That is the point this page works through for what is 3.31 gear ratio.

Taking what is 3.31 gear ratio as the case in point: The short version is that 3.31 sits in the middle of the ratios commonly fitted to cars and light trucks: shorter than a 3.21, taller than a 4.10, and a compromise between pulling power and quiet cruising. Whether it is the right ratio for a particular vehicle depends on the tyre diameter, the weight being moved and how the vehicle is used, so the worked example below uses 205/55R16 tyres (631.9 mm, 24.88 in) and shows the RPM at the speeds that matter, and a comparison table puts 3.31 next to 3.07, 3.55 and 4.10 so the difference is visible rather than guessed. Every figure is a calculation from the stated inputs, and the disclaimer below applies to all of it.

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.

what is 3.31 gear ratio: How the gear ratio formula works

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 what is 3.31 gear ratio.

What a gear ratio is for what is 3.31 gear ratio

For what is 3.31 gear ratio, the point is this: Every driven axle has a ratio, and it is one of the numbers that decides how a vehicle behaves. It is the ratio between driveshaft speed and wheel speed, fixed by the ring gear and pinion teeth inside the differential. A 3.21 ratio turns the driveshaft 3.21 times per wheel revolution; a 4.56 turns it 4.56 times. Because the engine is connected to the driveshaft through the gearbox, the axle ratio directly sets how fast the engine spins at any road speed in any gear. Change the ratio and the whole speed-versus-RPM relationship shifts: the same speed needs more or fewer engine revolutions, the same engine speed gives a different road speed, and the torque at the wheels changes in proportion. That is why the ratio matters whenever tyres get bigger, a trailer gets heavier, or the way the vehicle is used changes.

Worked example: 3.31 ratio at 30, 50 and 70 mph for what is 3.31 gear ratio

Take a 3.31 axle ratio on 205/55R16 tyres (631.9 mm, 24.88 in), in top gear at 1.00. At 70 mph the formula gives RPM = (70 × 1.00 × 3.31 × 336) ÷ 24.88 = 3,129 RPM. At 50 mph the same calculation gives RPM = (50 × 1.00 × 3.31 × 336) ÷ 24.88 = 2,235 RPM, and at 30 mph it gives 1,341 RPM. The speed at 2,000 RPM is (2,000 × 24.88) ÷ (1.00 × 3.31 × 336) = 44.7 mph, and at 3,000 RPM it is 67.1 mph. Each of those numbers can be re-checked with the formula above, and changing the tyre diameter changes all of them in proportion — a 10% larger diameter cuts every RPM figure by roughly 9%. That is the point this page works through for what is 3.31 gear ratio.

what is 3.31 gear ratio: RPM table: 3.31 against 3.07, 3.55 and 4.10

For what is 3.31 gear ratio, the point is this: Assumption: 205/55R16 tyres (631.9 mm, 24.88 in), top gear 1.00. RPM = (speed × ratio × 336) ÷ 24.88.

Speed 3.07 ratio 3.31 ratio 3.55 ratio 4.10 ratio
30 mph 1,244 RPM 1,341 RPM 1,438 RPM 1,661 RPM
50 mph 2,073 RPM 2,235 RPM 2,397 RPM 2,768 RPM
70 mph 2,902 RPM 3,129 RPM 3,356 RPM 3,876 RPM

Taking what is 3.31 gear ratio as the case in point: Read across any row and the trade is visible: at 70 mph the 3.31 ratio sits between the taller 3.07 and the shorter 4.10, and the gap between the extremes is about a third of the engine speed. That gap is the difference between a relaxed cruise and a busy one, and between soft acceleration and strong acceleration, which is why the ratio is chosen from the table rather than from the number alone. If the tyres are larger than the assumption here, every RPM figure falls; if they are smaller, every figure rises — rework the table with the actual diameter before deciding.

How tyre diameter changes the answer for what is 3.31 gear ratio

On this page, what is 3.31 gear ratio is the case in point: Diameter matters because the formula divides by it. Double the tyre diameter and the RPM at a given speed halves; increase it by 10% and the RPM falls by roughly 9%. That relationship is also why the speedometer changes with tyre size: the speedometer assumes a fixed number of wheel revolutions per mile, and a bigger tyre covers the mile in fewer revolutions. When this article quotes a tyre diameter it is the nominal new-tyre figure from the size code — for example 205/55R16 measures 631.9 mm, or 24.88 inches — and real tyres vary slightly by brand, model, wear and inflation pressure, so the RPM numbers that follow are good to within a small margin rather than exact.

What the ratio does on the road for what is 3.31 gear ratio

On this page, what is 3.31 gear ratio is 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 what is 3.31 gear ratio

Taking what is 3.31 gear ratio as the case in point: The ratio on the vehicle can be found in several ways, and checking two of them is worth the effort. Start with the metal tag on the differential cover, which usually carries the ratio as a stamped number. Then check the door-jamb placard and the owner's manual, which list the specification as the vehicle left the factory. The VIN can be run through a decoder or the manufacturer's parts system, which returns the build specification including the axle — useful, but it describes the vehicle as built, not as modified, so a swapped axle will not show up. The definitive check is the tooth count: with the differential cover off, count the teeth on the ring gear and on the pinion and divide the first by the second. A 41-tooth ring gear with an 11-tooth pinion is 41 ÷ 11 = 3.73. When the sources disagree, the physical count wins.

Common mistakes with gear ratios for what is 3.31 gear ratio

For what is 3.31 gear ratio, the point is this: A few errors recur in almost every gear-ratio discussion. One is using the tyre's advertised size instead of its measured diameter — a 35-inch tyre is a nominal size, and the real rolling diameter is what the formula wants, so the table's assumption should be read before the numbers are used. Another is mixing up the direction: a numerically higher ratio is shorter gearing, not taller, so 4.10 gives more RPM than 3.73 at the same speed. A third is ignoring overdrive — many modern gearboxes top out below 1.00, sometimes well below, which lowers cruising RPM far more than the axle ratio alone suggests. A fourth is expecting the ratio to fix a problem it cannot: it changes RPM and torque multiplication, but it does not change the engine's power, the vehicle's weight or the aerodynamics. And the last is the safety error — presenting the calculation as a fitment approval instead of checking the placard and confirming with a tyre professional.

Related pages for what is 3.31 gear ratio

Frequently asked questions

What RPM does a 3.31 gear ratio give at 70 mph?

Taking what is 3.31 gear ratio as the case in point: On 205/55R16 tyres (631.9 mm, 24.88 in) in top gear at 1.00, a 3.31 ratio gives 3,129 RPM at 70 mph, 2,235 RPM at 50 mph and 1,341 RPM at 30 mph. Those figures use the stated tyre diameter, so rework them with the actual diameter for a different tyre size — a 10% larger diameter cuts every RPM figure by roughly 9%.

Is a 3.31 gear ratio good for towing?

A 3.31 ratio is a middle-ground choice for towing: it multiplies torque more than a taller ratio such as 3.21, so it holds speed better on grades with a trailer, but less than a shorter ratio such as 4.10. Whether it suits a particular towing job depends on the trailer weight, the tyre diameter and the engine, so use the RPM table above with the actual figures and confirm with a drivetrain specialist. Never exceed the vehicle's tow rating, GVWR or GCWR.

How do I find out if my car has a 3.31 gear ratio?

Taking what is 3.31 gear ratio as the case in point: Check the metal tag on the differential cover, which usually stamps the ratio directly, then cross-check the door-jamb placard and the owner's manual. A VIN decoder returns the ratio the vehicle was built with. The conclusive check is counting teeth: divide the ring-gear teeth by the pinion teeth, so 41 ÷ 11 = 3.73. If the sources disagree, the tooth count describes the axle actually fitted.

Does changing the gear ratio affect the speedometer?

Taking what is 3.31 gear ratio as 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, what is 3.31 gear ratio 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.