What Is 3.73 Gear Ratio: RPM, Speed & What 3.73 Means on the Road

On this page, what is 3.73 gear ratio is the case in point: A 3.73 gear ratio means the driveshaft turns 3.73 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 3.73 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.

Taking what is 3.73 gear ratio as the case in point: The short version is that 3.73 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 3.73 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.

How the gear ratio formula works for what is 3.73 gear ratio

For what is 3.73 gear ratio, the point is this: The formula that ties speed, ratio and tyre size together is RPM = (speed × gear ratio × final drive × 336) ÷ tyre diameter in inches. Speed is in miles per hour, gear ratio is the gearbox gear in use, final drive is the axle ratio, and 336 is the constant that converts miles, hours and inches into revolutions per minute. In top gear on most gearboxes the gear ratio is 1.00, so the formula simplifies to RPM = (speed × final drive × 336) ÷ tyre diameter. Turn it around and it gives speed from RPM: speed = (RPM × tyre diameter) ÷ (gear ratio × final drive × 336). Both directions use the same numbers, so a table built from one can be checked from the other, and any result can be verified by hand with a pocket calculator. The tyre diameter used here is the nominal new-tyre figure; real tyres vary slightly by brand, model, wear and inflation pressure.

what is 3.73 gear ratio: What a gear ratio is

On this page, what is 3.73 gear ratio is the case in point: A gear ratio describes how many times the driveshaft turns for each turn of the wheels. A 3.73 axle ratio means the driveshaft rotates 3.73 times while each wheel rotates once, and a 4.10 ratio means the driveshaft rotates 4.10 times for that same single wheel rotation. The number is fixed by the ring gear and pinion inside the differential: divide the number of teeth on the ring gear by the number on the pinion and you get the ratio. A higher number is called a shorter or lower gear, because it multiplies engine torque more and keeps the engine spinning faster at any road speed; a lower number is called a taller or higher gear, because it does the opposite. Neither is better in the abstract — the right ratio depends on the tyre diameter, the weight being moved, the engine's power band and how the vehicle is used.

what is 3.73 gear ratio: Worked example: 3.73 ratio at 30, 50 and 70 mph

Taking what is 3.73 gear ratio as the case in point: Take a 3.73 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 × 3.73 × 336) ÷ 24.88 = 3,526 RPM. At 50 mph the same calculation gives RPM = (50 × 1.00 × 3.73 × 336) ÷ 24.88 = 2,519 RPM, and at 30 mph it gives 1,511 RPM. The speed at 2,000 RPM is (2,000 × 24.88) ÷ (1.00 × 3.73 × 336) = 39.7 mph, and at 3,000 RPM it is 59.6 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%.

RPM table: 3.73 against 3.07, 3.55 and 4.10 for what is 3.73 gear ratio

Assumption: 205/55R16 tyres (631.9 mm, 24.88 in), top gear 1.00. RPM = (speed × ratio × 336) ÷ 24.88. That is the point this page works through for what is 3.73 gear ratio.

Speed 3.07 ratio 3.55 ratio 3.73 ratio 4.10 ratio
30 mph 1,244 RPM 1,438 RPM 1,511 RPM 1,661 RPM
50 mph 2,073 RPM 2,397 RPM 2,519 RPM 2,768 RPM
70 mph 2,902 RPM 3,356 RPM 3,526 RPM 3,876 RPM

On this page, what is 3.73 gear ratio is the case in point: Read across any row and the trade is visible: at 70 mph the 3.73 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.

what is 3.73 gear ratio: How tyre diameter changes the answer

For what is 3.73 gear ratio, the point is this: 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 3.73 gear ratio

On this page, what is 3.73 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.

what is 3.73 gear ratio: How to find the ratio already fitted

On this page, what is 3.73 gear ratio is 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 3.73 gear ratio

For what is 3.73 gear ratio, the point is this: Mistakes usually come from using half the formula. The first is to pick a ratio from a chart without entering the actual tyre diameter — the chart's assumption may be a different size from the tyres on the vehicle, and the answer follows the assumption, not the vehicle. The second is to forget that the gearbox gear matters: first gear multiplies torque far more than top gear, so a crawl or launch question needs the first-gear ratio while a cruising question needs top gear. The third is to read a higher ratio as simply better: it raises cruising RPM, which can raise noise and fuel use on long motorway runs, so the gain in acceleration is paid for at cruising speed. The fourth is to trust a ratio stamped on an axle tag without checking that the axle is original to the vehicle — a swapped axle carries its own ratio. And the fifth is to treat the calculation as permission: the maths says what the RPM will be, not that the change is suitable, so a drivetrain specialist should confirm the choice before parts are ordered.

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Frequently asked questions

What RPM does a 3.73 gear ratio give at 70 mph?

Taking what is 3.73 gear ratio as the case in point: On 205/55R16 tyres (631.9 mm, 24.88 in) in top gear at 1.00, a 3.73 ratio gives 3,526 RPM at 70 mph, 2,519 RPM at 50 mph and 1,511 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 3.73 gear ratio good for towing?

A 3.73 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 3.73 gear ratio?

On this page, what is 3.73 gear ratio is 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?

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. That is the point this page works through for what is 3.73 gear ratio.

Can I change my gear ratio myself?

On this page, what is 3.73 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.