BMW 318is - Better Mileage With Gearing? Ask Rob About Cars

Hi Rob,
Great articles and photos, thanks so much ,
I have a 1994 BMW 318is. It gets great gas mileage and would love to get even better mileage . The rear end (3rd) member locked up when I first got the car, so I found a deal on a 325 axles and rear end , put it in never changed any gears do you know if the 325 is different than the 318is both were manual transmissions. Should I leave well enough alone ?
Thanks,
FAN

Hello Fan and thank you!
I found this excellent website that lists a LOT of BMW gear ratios, perhaps all of them: http://www.bokchoys.com/differential/GearRatios.htm

It seems that you now have a less-aggressive final drive ratio of 3.15 vs. 3.45. So if you like your mileage and the acceleration is adequate, I would leave it alone and congratulate yourself on a fuel saving modification.

I wouldn't suggest trying anything numerically lower than 3.15 such as the 2.93, even if you can find it. My concern would be inadequate acceleration with the 4-cylinder engine. This would mean using higher revs and consuming more gas, effectively negating your intended result. Also, it may mean using a higher gear for cruising at certain speeds and poor acceleration in 5th gear. If you know anyone that has done it, be sure to write back and share!

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