Common Gear Ratios Chart: Ratios, RPM & Speed Compared

For common gear ratios chart, the point is this: A differential gear ratio chart puts the common axle ratios side by side so the trade between them can be seen at a glance: the RPM at a given speed, the speed at a given RPM, and how far each ratio moves the engine speed. This page is that chart, built from the formula RPM = (speed × gear ratio × final drive × 336) ÷ tyre diameter in inches, with the assumptions stated next to every table so the numbers can be reworked for a different tyre size. The tables assume 28-inch tyres (example diameter) and a 1:1 top gear unless stated otherwise, and the sections after the tables explain what the numbers mean for acceleration, cruising, towing and fuel use, and how to read the chart for a vehicle with different tyres.

On this page, common gear ratios chart is the case in point: The chart covers the ratios most often fitted to cars and light trucks, from tall cruising ratios around 3.07 to short ratios around 4.10 and beyond, and the RPM table shows all of them at 30, 50 and 70 mph so the spread is visible in one place. A 3.07 and a 4.10 differ by about a third in engine speed at any road speed, which is why the choice matters as much as it does — and why it should be made from the table with the actual tyre diameter rather than from the ratio number alone. The worked example below shows the arithmetic for one ratio so any line of the chart can be verified by hand.

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 common gear ratios chart

Taking common gear ratios chart as the case in point: Two formulas do the work, and both are worth knowing because they let any gear-ratio result be checked by hand. Engine speed is RPM = (speed × gear ratio × final drive × 336) ÷ tyre diameter in inches, where speed is in miles per hour and the tyre diameter is the nominal new-tyre diameter. Road speed is the same relationship rearranged: speed = (RPM × tyre diameter) ÷ (gear ratio × final drive × 336). The 336 is a unit-conversion constant, not a measured quantity, so it never changes. In a 1:1 top gear the gear ratio drops out and RPM depends only on speed, the axle ratio and the tyre diameter — which is why a ratio change or a tyre change shows up immediately as a different cruising RPM. Work through the formula once with your own numbers and the tables below stop being something to take on trust.

common gear ratios chart: What a gear ratio is

Taking common gear ratios chart as 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.

Worked example: RPM at 30, 50 and 70 mph for common gear ratios chart

Taking common gear ratios chart as the case in point: Take a 3.73 axle ratio on 28-inch tyres (example diameter), in top gear at 1.00. At 70 mph the formula gives RPM = (70 × 1.00 × 3.73 × 336) ÷ 28 = 3,133 RPM. At 50 mph it gives 2,238 RPM and at 30 mph 1,343 RPM. The speed at 2,000 RPM is 44.7 mph and at 3,000 RPM it is 67.0 mph. With a 3.07 ratio the 70 mph figure falls to 2,579 RPM, and with a 4.10 it rises to 3,444 RPM — the full spread is in the table below, and every line of it comes from the same formula with the same stated assumption.

RPM table: 3.07, 3.55 and 4.10 at 30, 50 and 70 mph for common gear ratios chart

Taking common gear ratios chart as the case in point: Assumption: 28-inch tyres (example diameter), top gear 1.00. RPM = (speed × ratio × 336) ÷ 28.

Speed 3.07 ratio 3.55 ratio 3.73 ratio 4.10 ratio
30 mph 1,105 RPM 1,278 RPM 1,343 RPM 1,476 RPM
50 mph 1,842 RPM 2,130 RPM 2,238 RPM 2,460 RPM
70 mph 2,579 RPM 2,982 RPM 3,133 RPM 3,444 RPM

On this page, common gear ratios chart is the case in point: The table makes the trade concrete. At 70 mph the 3.07 cruises at the lowest RPM and the 4.10 at the highest, with a gap of about a third between them, and the same gap appears at 30 and 50 mph because the ratio multiplies the RPM at every speed. A taller ratio suits a vehicle that spends its life cruising; a shorter ratio suits one that tows, climbs or runs bigger tyres. The middle ratios are the compromise, and the worked example above shows how to rework any line of the table for a different tyre diameter: divide the table's RPM by the old diameter and multiply by the new one, or run the formula again from the start.

How tyre diameter changes the answer for common gear ratios chart

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. That is the point this page works through for common gear ratios chart.

common gear ratios chart: What the ratio does on the road

On this page, common gear ratios chart is the case in point: A ratio is a trade between pulling power and cruising calm, and the tables below make the trade visible. Raising the number lifts the RPM at every speed: the engine works in a stronger part of its range, the vehicle accelerates harder and tows with less strain, but the motorway cruise gets busier and thirstier. Lowering the number drops the RPM everywhere: the cruise gets quieter and usually cheaper, while acceleration softens and the gearbox works harder on grades. The size of the effect is not subtle — moving from 3.21 to 4.10 is a 28% change in RPM at any speed — so a ratio change is one of the biggest single changes that can be made to how a vehicle drives. It is also why the choice should be made from the RPM table with the actual tyre diameter, not from the ratio number alone.

How to find the ratio already fitted for common gear ratios chart

For common gear ratios chart, the point is this: 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 gear ratios chart: Common mistakes with gear ratios

On this page, common gear ratios chart is the case in point: 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.

common gear ratios chart: Related pages

Frequently asked questions

How do I work out the RPM for common gear ratios chart?

On this page, common gear ratios chart is the case in point: Use RPM = (speed × gear ratio × final drive × 336) ÷ tyre diameter in inches, with the gear in use and the axle ratio for the vehicle. The worked example above shows the arithmetic at 30, 50 and 70 mph with the assumptions stated, and the gear ratio calculator runs the same formula with your own numbers.

What does a higher gear ratio do?

For common gear ratios chart, the point is this: A numerically higher ratio — a shorter gear — raises engine speed at every road speed, multiplies torque more at the wheels, sharpens acceleration and helps towing, at the cost of higher cruising RPM and usually more fuel on steady motorway runs. A lower number does the opposite. The table above shows the RPM for several ratios side by side so the trade is visible.

How does tyre size affect gear ratio?

A larger tyre diameter makes the effective gearing taller: the vehicle travels further per wheel revolution, so the engine turns more slowly at a given road speed. A 10% larger diameter cuts cruising RPM by roughly 9% with the same ratio. That is why bigger tyres are usually paired with a numerically higher ratio, to restore the RPM the vehicle had before the tyre change. That is the point this page works through for common gear ratios chart.

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 common gear ratios chart.

Can I change my gear ratio myself?

For common gear ratios chart, the point is this: 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.