Gear Ratio Calculator
Speed at any RPM in every gear, plus a drive simulator
Pick a T5, T56, Toploader or custom transmission, then enter your axle ratio and tire size to see real-world speeds in each gear. Press Simulate Drive to watch the gauges rev through each gear and shift at your shift point. Go to the simulator
Note: Always verify calculations independently before purchasing parts. Results are estimates and may vary based on actual tire dimensions, manufacturing tolerances, and wear.
Transmission
Don't know your ratio? Look it up by your axle tag
Tire Size
Calculated Diameter: 25.68"
Changing tires? Compare it with another size
Performance at 3,000 RPM
Engine RPM
Shift Point RPM
Speed in Each Gear at 3,000 RPM
| Gear | Ratio | Speed (mph) | Shift @ 5,500 |
|---|---|---|---|
| 1 | 3.35 | 18.3 mph | 33.6 mph |
| 2 | 1.93 | 31.8 mph | 58.4 mph |
| 3◀ | 1.29 | 47.6 mph | 87.3 mph |
| 4 | 1.00 | 61.4 mph | 112.7 mph |
| 5 | 0.68 | 90.4 mph | — |
How speed at RPM is worked out
Road speed in any gear comes from four numbers: engine RPM, that gear's ratio, the axle ratio and the tire's diameter. The calculator uses this formula:
mph = RPM × tire diameter × π ÷ (gear ratio × axle ratio × 1,056)
Tire diameter × π is how far the tire rolls in one turn, in inches. Dividing that by the gear and axle ratios gives inches travelled per engine turn, so multiplying by RPM gives inches per minute. 1,056 converts inches per minute to miles per hour (63,360 inches in a mile ÷ 60 minutes in an hour).
Example: a V8 World Class (85-89) T5 in fifth (0.68), a 3.73 axle and 245/45R17 tires (25.68" tall) at 3,000 RPM: 3,000 × 25.681 × π ÷ (0.68 × 3.73 × 1,056) = 90.4 mph.
Finding your axle ratio
The ratio is stamped on the tag held under one of the bolts on the rear end's center section, on the line that starts with a number: 3 00 is a 3.00 ratio, and an L in place of the space (3L00) means a locking differential. The other line is the axle code, such as WDY-A, which the Ford rear axle tag guide turns into the ratio, ring gear size and original cars for every Ford car from 1963 to 1980.
If the tag is gone or the gears may have been changed, count it. With both rear wheels off the ground and the transmission in neutral, mark the driveshaft and a tire, turn the tire one full turn and count the driveshaft's turns: three and a half turns is about a 3.50.
Fifth gear speed at 2,000 and 3,000 RPM
For each fifth gear ratio in the calculator's T5 presets, with 245/45R17 tires (25.68" tall, the calculator's default). Like the calculator, the speeds use the unrounded diameter, 25.681". A different tire size changes every number in proportion; see below.
| Axle ratio | 0.68 fifthV8 World Class (85-89), V8 World Class (90-95), Cobra (93-95) | 0.79 fifth2.3L 4-Cylinder | 0.63 fifthGM V8 (Camaro/Firebird) | |||
|---|---|---|---|---|---|---|
| 2,000 RPM | 3,000 RPM | 2,000 RPM | 3,000 RPM | 2,000 RPM | 3,000 RPM | |
| 2.73 | 82.3 | 123.5 | 70.9 | 106.3 | 88.8 | 133.3 |
| 2.79 | 80.5 | 120.8 | 69.3 | 104.0 | 86.9 | 130.4 |
| 3.08 | 73.0 | 109.4 | 62.8 | 94.2 | 78.7 | 118.1 |
| 3.27 | 68.7 | 103.1 | 59.2 | 88.7 | 74.2 | 111.3 |
| 3.31 | 67.9 | 101.8 | 58.4 | 87.7 | 73.3 | 109.9 |
| 3.55 | 63.3 | 94.9 | 54.5 | 81.7 | 68.3 | 102.5 |
| 3.73 | 60.2 | 90.4 | 51.9 | 77.8 | 65.0 | 97.5 |
| 3.90 | 57.6 | 86.4 | 49.6 | 74.4 | 62.2 | 93.3 |
| 4.10 | 54.8 | 82.2 | 47.2 | 70.8 | 59.2 | 88.7 |
| 4.30 | 52.3 | 78.4 | 45.0 | 67.5 | 56.4 | 84.6 |
| 4.56 | 49.3 | 73.9 | 42.4 | 63.6 | 53.2 | 79.8 |
Speeds in mph.
How tire size changes speed
Speed at a given RPM rises in step with tire diameter: a tire 3% taller gives 3% more speed at the same RPM. For a metric size such as 245/45R17, the calculator works out the diameter as rim + 2 × width × aspect ÷ 100 ÷ 25.4. For 245/45R17 that's 17 + 2 × 245 × 45 ÷ 100 ÷ 25.4 = 25.681 inches.
Changing tire size or axle ratio also changes what a T5's speedometer reads, since it is driven by a gear in the transmission. The T5 speedometer gear calculator works out which gear you need.
Transmission presets
The calculator's presets, with the rows of the T5 identification guide that list the same five forward ratios. Rows are matched on ratios alone, so a list can include other cars and aftermarket units that use the same gears. Select a tag to see its row. The Toploader presets are the two gearsets of the 1964–1973 Ford four-speed; its tag tells you which one you have.
The V8 presets follow the T5 guide, where the 1.99 second gear starts in 1990. Some sources, such as Modern Driveline, put the change at 1989. Check the tag on your transmission.
| Preset | Ratios | T5 guide rows with these ratios |
|---|---|---|
| V8 World Class (85-89) | 3.35, 1.93, 1.29, 1.00, 0.68 | 13-52-126, 13-52-141, 13-52-165, 13-52-169 |
| V8 World Class (90-95) | 3.35, 1.99, 1.33, 1.00, 0.68 | 13-52-199, 13-52-204, 13-52-208, 13-52-218, 13-52-219, 13-52-239, 13-52-242, 13-52-246, 13-52-253 |
| 2.3L 4-Cylinder | 3.97, 2.34, 1.46, 1.00, 0.79 | 13-52-155, 13-52-162, 13-52-194, 13-52-207, 13-52-209 |
| GM V8 (Camaro/Firebird) | 2.95, 1.94, 1.34, 1.00, 0.63 | 13-52-72, 13-52-115, 13-52-166, 13-52-182, 13-52-200, 13-52-227, 13-52-249, 13-52-251 |
| Cobra (93-95) | 3.35, 1.99, 1.33, 1.00, 0.68 | 13-52-199, 13-52-204, 13-52-208, 13-52-218, 13-52-219, 13-52-239, 13-52-242, 13-52-246, 13-52-253 |
| T56 6-Speed (F-body/Corvette) | 2.66, 1.78, 1.30, 1.00, 0.74, 0.50 | Not a T5. Ratios from TX Drivetrain |
| T56 6-Speed (03-04 Cobra) | 2.66, 1.78, 1.30, 1.00, 0.80, 0.63 | Not a T5. Ratios from Modern Driveline |
| Toploader 4-Speed Close Ratio | 2.32, 1.69, 1.29, 1.00 | Not a T5. Ratios and tag codes in the Toploader identification guide |
| Toploader 4-Speed Wide Ratio | 2.78, 1.93, 1.36, 1.00 | Not a T5. Ratios and tag codes in the Toploader identification guide |