Best LSD Gear Ratio for Daily Driving

[Since88]

Well I just pick up an 1988 325ic Manual transmission w/ 165k Bone Stock rolling on stock wheels (bottle caps). The car is in good running condition except for the rear end noise I'm experiencing while driving above 30 mph. Sound does not change when in neutral and coasting down the highway. Had a mechanic took a look at it and told me it could be the pinion bearing within the diff. I tried changing the fluid and recently replaced the rear brakes (pads, rotors) and whining noise is still presence. Worst case, if I were to replace the diff I was thinking about getting lsd, (noob question) what is the best gear ratio for daily driving as I too take the highway to work. Does it affect the speedometer? I know for sure the rpm will have a slight change depending on diff ratio. If it does affect the speedometer, will I have to change something like the speed sensor?

Did a little research...3.73 seems to be best all around. What do you guys think?

[jlevie]

A 3.73, like what is in the car now is the best choice for mixed urban and rural driving.

[EatsHondas]

3.73 baby. I have one and I love it. It's a little short for an M30, but I can still hit 140 on the speedo. That's stupid fast in a tiny little e30. That being said, I'm not going to think about changing the rear end again until after a turbo install.

I had a 4.10 in the stock M20. It was noticeably "quicker" through the gears, but no amount of gearing can make up for lack of torque. 4000 rpm at 80mph was also very annoying.

[Hooffenstein HD]

3.73, or 3.91.

[jeffnhiscars]

Don't rule out the possibility that it is a wheel bearing which should be replaced in pairs...and yes to a 3.73. I have one in my cabrioand at 80mph I'm turning about 2800rpm w an auto trans

[Since88]

Shout out to all the inputs...I will get a second opinion on the rear end noise before I ruled out the wheel bearings..just curious is the 3.73 lsd only comes in the 325is coupe? (After 88+)