Quick Intro to BMW Gear Ratios

What is a BMW gear ratio? A modern day transmission consists of multiple gears, with different gear ratios, inside the gearbox and the primary purpose is to maximize the energy produced by the engine. If there was no transmission and the power being delivered to the crankshaft was directly connected to the driveshaft to spin the wheels, your maximum speed is only as great as what the engine can provide. However with multiple BMW gear ratio inside a transmission, the engine’s power can be harvested to allow greater top speed without the engine spinning faster, thus being efficient as well.

An S54 E46 M3 engine can produce a maximum of 8,000 RPM to the crankshaft. You can have no transmission and have a top speed of 60 mph at 8,000 RPM or you can add a transmission with different BMW gear ratio to go 155 mph, while still being at 8,000 RPM.

How Do BMW Gear Ratio Work?

You have 2 RC car tires. Tire A has a circumference of 1 inch. Tire B has a circumference of 2 inches. If you roll both tires equally on the ground starting at the same point, Tire A will need to roll two full rotations to cover the same distance as tire B. What does that mean? Tire A has to rotate faster. Take this concept over to gears and you have a gearbox with a 2:1 gear ratio.

Transmission gears have teeth on them to prevent slippage. A BMW gear ratio of 2:1 can have a gear with 60 teeth and 30 teeth. You can also calculate the gear ratio, such as one found in a differential, by dividing the two.

BMW Gear Ratio Table

Below is a compilation of BMW gear ratio found on BMW transmissions and also the final drive ratios on the differential. This is a work in progress and I will continue to spend hours manually scavenging through official BMW brochures to compile. Baseline guides are already out there, but mostly scattered all over the internet so I took the time to compile in one list and also adding new data points for the newer cars such as the 7-speed DCT transmission, etc. If you see any corrections, please comment below.

Differential final drive, separate from transmission gearing, ratios are also listed. A lot of people talk about changing their diff ratio e.g. upgrading to 3.91 or 4.10 on the Getrag 420G 6-speed transmission for E46 M3. Without getting into too much detail, the differential has significant impact on the overall gearing of the transmission and can improve drivability on the streets or track.

Should I Upgrade My Differential Final Drive?

A higher ratio final drive will provide more torque at the wheels and faster acceleration, but a lower top speed – and vice versa for lower final drive. The final drive itself is usually cheaper than the install. Installation requires you to drop your differential and open up the case so that’s where a lot of the money is spent. I would estimate around $2,200 for parts and labor for final drive swap on an E46 M3.

Is it worth it? I don’t think it’s worth it unless you feel like you maximized your potential on track. On track, the final drive is more about shifting and power band optimization more than it is for quicker acceleration. Another thing you can try before a final drive swap is to get shorter profile or smaller diameter tires. That allows a full rotation to happen faster on the car, so same principles as getting a shorter final drive. We list the differential/gearing upgrade for hardcore track enthusiasts in our Essential E46 M3 Track Day Mods.