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  • Question re rear diff

    I am interested in swapping out my rear diff... has anyone done this before? What is the recommended raftio for occasional street and highway driving?

  • #2
    Need more information. What transmission you are running...tire size....etc.

    But in general for street/highway driving stock is a good compromise.

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    • #3
      I am stock minus my wheels I have 17 inch bbs rs

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      • #4
        I agree with Ironhead. Stock is usually best for all around street / highway driving. If you track the car, then I like a 4.27 ratio with an overdrive gearbox and 15" wheels.
        Ron ///Man

        • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
        • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
        • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
        • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
        • '89 M3 M3T / ITR Club Racer
        • '94 Spec E36 - Eh....
        • '09 M3 - Tarmac Terrorist
        • '04 330Xi Sport 6 Speed - Snowmobile
        • '07 530 Xi - Highway Star
        • http://www.imwcarparts.com/e30-m3-parts.htm


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        • #5
          What about the 4.45 would that be to short?

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          • #6
            I agree with all of the above. These cars are geared really nicely stock.
            I have a 3.91 in my Cabrio and its a little nicer cruising on the highway, but between the cabrio weight and the slightly taller gear my street M3 accelerates much harder.
            I have a shelf full of diffs (well not as many as Ron LOL) and I have never thought about changing the one in my street car.
            If the car is stock and you are just driving on the street, even "occasional" track I wouldnt change a thing.
            If you start tracking more, I'd look at a 4.27 as Ron suggested.
            Last edited by jimmy p.; 11-10-2018, 05:36 AM.
            jimmy p.
            87 E30 M3 Prodrive British Touring Car
            88 E30 M3 Zinnoberot - Street
            88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
            92 E30 M Technic Cabrio - S14 POWERED!
            98 318Ti M44, Base - Morea Green
            04 Ford F350 - V10

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            • #7
              Originally posted by Afonsom3 View Post
              What about the 4.45 would that be to short?
              I think 4.45 would be too short for highway driving but would work OK for around town and City driving. It would also work well as a short track diff with a US OD gearbox.
              Ron ///Man

              • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
              • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
              • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
              • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
              • '89 M3 M3T / ITR Club Racer
              • '94 Spec E36 - Eh....
              • '09 M3 - Tarmac Terrorist
              • '04 330Xi Sport 6 Speed - Snowmobile
              • '07 530 Xi - Highway Star
              • http://www.imwcarparts.com/e30-m3-parts.htm


              Comment


              • #8
                Alfonso, what size tires are you running? Your actual tire diameter (especially with the 17" wheels) will help determine how much shorter you might want to go on the rear final drive.

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                • #9
                  My car is mostly a track car, but I drive it to and from track events. I am running the 4.45 final drive with 235/40-17 tires and the US spec 265 OD trans. I don't remember the exact RPMs, but on the freeway at 75-80 MPH in 5th it is really buzzing along. Doesn't bother me for my purposes, but I would not want to drive it across the USA or anything.

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                  • #10
                    Soon fifth at 75 miles an hour what rpm are you app

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                    • #11
                      I have 17 inch BBSRS front wheels are 8 1/2 rears are 9.5. Tires I believe I have 225 45 in the front and 245 25 in the rear

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