[johnung]

Anyone have any insight as to the rear final drive ratio on an F34 2015 320i GT RWD with a manual transmission?

Realoem appears to list two rear differential options with the manual transmission: (see photo) The first they are calling an exchange.

1) 33107599470, 3.23 Final Drive Ratio
2) 33107603750, 3.91 Final Drive Ratio

Not sure if a visual inspection of the stock rear differential on the car would help. Anyone know if a BMW part number can be found on the rear differential and its possible location?

[Oksamit78]

Use VIN number on Real OEM if you can't crawl under the car to get the P/No off the rear differential.

I can see a sticker on the back wall of the differential case if I look diagonal from behind the left wheel.

[johnung]

Originally Posted by Oksamit78

Use VIN number on Real OEM if you can't crawl under the car to get the P/No off the rear differential.

The photo that I posted is from Realoem which lists two different parts when the VIN is entered. That’s the issue.

[Ragnar The Redneck]

That first one, 3.23:1 ratio sounds closer to the six cylinders 3.08, which would lead me to believe that would be for a 4-cylinder diesel engine, not 4-cylinder gas engine. The 3.91 sounds like what a 4-cylinder gas engine would have.

Before assuming anything, though, you will need to find the tag on the differential, it should have the part number on it, or it could have a cryptic number like 34:11, which would equate to 3.09 (34 / 11).

If that fails, you can always mark the bottom of the tire and the bottom of the drive shaft and count how many times the drive shaft spins around when you spin the wheel once. If you count that the driveshaft spins 3 and 1/4 times around that would be about 3.23 ratio, 3 and 9/10 or almost 4 turns would be 3.91.

If you cannot see the tag on the rear, if you have xDrive, you can check the front diff, as both diffs should have the same axle ratio.

[johnung]

Originally Posted by Ragnar The Redneck

That first one, 3.23:1 ratio sounds closer to the six cylinders 3.08, which would lead me to believe that would be for a 4-cylinder diesel engine, not 4-cylinder gas engine. The 3.91 sounds like what a 4-cylinder gas engine would have.

Before assuming anything, though, you will need to find the tag on the differential, it should have the part number on it, or it could have a cryptic number like 34:11, which would equate to 3.09 (34 / 11).

If that fails, you can always mark the bottom of the tire and the bottom of the drive shaft and count how many times the drive shaft spins around when you spin the wheel once. If you count that the driveshaft spins 3 and 1/4 times around that would be about 3.23 ratio, 3 and 9/10 or almost 4 turns would be 3.91.

If you cannot see the tag on the rear, if you have xDrive, you can check the front diff, as both diffs should have the same axle ratio.

Thanks! That was very helpful!

[Oksamit78]

Originally Posted by Ragnar The Redneck

That first one, 3.23:1 ratio sounds closer to the six cylinders 3.08, which would lead me to believe that would be for a 4-cylinder diesel engine, not 4-cylinder gas engine. The 3.91 sounds like what a 4-cylinder gas engine would have.

I see that GTs with the 4-cylinder diesels (320d) came with 3.38 in RWD Manual and with 2.81 in RWD Auto.

Like you said, I'd expect 3.91 be the one for 320i RWD Manual.

FYI: My 2017 XDrive GT with B58 (6 cylinder) has 2.93 front and rear.

[Ragnar The Redneck]

Originally Posted by Oksamit78

I see that GTs with the 4-cylinder diesels (320d) came with 3.38 in RWD Manual and with 2.81 in RWD Auto.

Like you said, I'd expect 3.91 be the one for 320i RWD Manual.

FYI: My 2017 XDrive GT with B58 (6 cylinder) has 2.93 front and rear.

Which is why I said to not assume anything. But, I didn't take my own advice, as I assumed a pre-LCI 320i... I loved the days when you could look at the series and know which size engine was in 95% of all BMWs. Some exceptions were the E30 325 (an e had a 2.7L I6, while an i had a 2.5) and early 528e's (well, they were close). I'm sure there were a few more, but most were spot on.

The B58 has a 2.93? Must have more torque available at a lower RPM than the N55 (what I have), as it has a 3.08.

[johnung]

POST UPDATE: The owner of the car was able to get under it and found a label on the top of the rear differential that indicated that it has a 3.23 final drive ratio.

[Ragnar The Redneck]

Originally Posted by johnung

POST UPDATE: The owner of the car was able to get under it and found a label on the top of the rear differential that indicated that it has a 3.23 final drive ratio.

Thanks for the update! I will need to update my info about how BMW installs FDRs. This would also seem to indicate that the turbo-4 gas engines are a bit better than I realized.