Gear Ratio Calculator

Start by entering your tire size. You can type the overall diameter in inches directly, or switch to tire notation mode and enter the metric size code from your tire sidewall (for example, 265/70R17). The calculator will convert the metric notation to an overall diameter automatically.

Next, enter your axle (ring and pinion) ratio. If you are not sure what ratio your vehicle has, check the RPO sticker in the glove box, the owner's manual, or use one of the common presets from the dropdown. Then enter the transmission gear ratios for each forward gear. You can leave any unused gear slots blank.

Set a target speed (such as 65 mph for highway cruising) and optionally enter your engine's redline RPM. The calculator will show you the RPM in every gear at that speed and the maximum theoretical speed in each gear at redline.

To compare a proposed axle ratio swap, enter a second ratio in the Compare Axle Ratio field. The results table will show RPM values for both ratios, and a side by side comparison highlights the difference at highway speed.

Every time power travels from your engine to the wheels, it passes through a series of gear reductions. The transmission provides one reduction that changes as you shift through the gears. The axle (also called the differential or ring and pinion) provides a second, fixed reduction. If your vehicle has a transfer case, it adds a third reduction. The product of all these reductions is the final drive ratio.

A higher numerical final drive ratio (like 14:1 in first gear) means the engine turns more revolutions for each wheel rotation. This creates more torque multiplication, which is why first gear feels powerful but has a low top speed. A lower ratio (like 2.5:1 in overdrive) means the engine turns fewer times per wheel revolution, which allows higher speed with less engine wear and noise.

The tire diameter also affects the effective gearing. Larger tires cover more ground per revolution, which has the same effect as lowering the axle ratio. This is why vehicles with oversized tires often feel sluggish until the axle gears are swapped for a numerically higher set.

The best axle ratio depends on how you use your vehicle. For daily driving and fuel economy, a lower numerical ratio (like 3.08 or 3.23) keeps highway RPM low and reduces engine wear over long distances. For towing, a higher ratio (like 4.10 or 4.56) provides more pulling power but increases RPM and fuel consumption at highway speed.

Off road vehicles often benefit from high axle ratios, especially after installing larger tires. A common approach is to calculate the RPM at highway speed with your original tire and axle combination, then find the axle ratio that produces similar RPM with the new, larger tires. This restores the driving characteristics and speedometer accuracy.

For example, if a truck with 30 inch tires and 3.73 gears turns 2,000 RPM at 65 mph, and you install 35 inch tires, you would need approximately 4.56 gears to return to the same highway RPM. Use the compare feature in this calculator to find the closest standard ratio for your situation.

Light duty pickup trucks often come with 3.42 or 3.73 axle ratios paired with six speed automatic transmissions. The 3.73 is popular for towing packages because it provides better acceleration under load, while the 3.42 is a good balance for mixed use driving.

Heavy duty trucks may use 3.73, 4.10, or even 4.30 ratios depending on the application. Trucks that regularly pull heavy trailers benefit from numerically higher ratios, while highway haulers that run mostly unloaded may prefer a milder ratio to save fuel.

Jeeps and off road SUVs commonly run 4.10 or 4.56 with stock tires, and 4.88 or 5.13 after a tire upgrade to 35 inches or larger. When paired with a transfer case that has a 2.72:1 low range (common in many Jeep models), a 4.88 axle and 4.46 first gear produces a crawl ratio of approximately 59:1, which is excellent for technical terrain.