3:55 gears on the street

Transmission and Drivetrain Tech

  1. 496 polara

    496 polara moparts id gch

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    3.55 gear is perfect for 90% of street driven cars.My Polara ran 3.55's with 28" tires (275/60r15) for years.
    Only reason to run 3.23 or lower (numerically) is for extended higher speed cruising.
     
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    • sdh148

      sdh148 Member

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      I am surprised how tall the tires are that people are using. Maybe I was ultra conservative, but, when I looked to fit new wheels/tires on my 68 Dart, I made a tire-shaped template and checked for clearance to the fenders, control arms, brakes, steering linkage, strut rod, and "frame rail" -- at various combinations of suspension travel (up to full jounce/rebound) and various steering angles (up to full lock). The biggest I could go on an 8 inch wide rim without anything rubbing was 225/35R18. This is about a 24 inch tire, which is the same diameter that the car originally came with when I got it (175/80R13).
       
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      • toolmanmike

        toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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        I wish I had a 3.55 at least. My 255-60-15's are 27" and didn't do my 3.23 gear change much good. 70 Swinger with 15x7 with 4.25" backspace.
         
      • pishta

        pishta I know I'm right....

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        did you ever get it out of second? :eek:
         
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        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          On my B body I have 3.55’s on a 245/60/15. I find this an excellent street driver combo. It revs a little high @ Hwy. speeds. No big deal I think. I tend to keep it a little slow on the Hwy. I’ve driven it for hours in a clip, no issues.
           
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          • toolmanmike

            toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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            Yep, I maybe drive 60 on the interstate going to car shows up to 4 hours away. I'm not in a hurry.
             
          • rumblefish360

            rumblefish360 So close, yet so far away FABO Gold Member

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            Exactly! 60/65, I’m good, no rush. I’ve done 70/75 and the secondary side tends to tip in. Not good for mileage. It takes a nose dive when the secondary side starts feeding the engine! LMAO!!!

            At the time, I had a smog era ‘78-400 B engine in it. 60 mph and 18 mpg’s, yea! I’m good with that!
            Go to 75 mph, mileage tanks!
             
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            • R4Sedan

              R4Sedan Larry FABO Gold Member

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              Problem is down here if you only drive 60/65 they run you off the road.
               
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              • rumblefish360

                rumblefish360 So close, yet so far away FABO Gold Member

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                LOL! On this island, 70/75 is the norm in any lane.
                So, I truly get it. I know some states have that speed as a regular posting. On the Island, it’s 55.
                 
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                • 69_340_GTS

                  69_340_GTS Well-Known Member

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                  25.5" tires will fit just fine. At stock ride height The 225/60-15 tires fit on my '69 Dart just fine, front and rear. Rear tire can easily be up to 28", but personally I like them all the same size. Either your car is severely lowered or you have the wrong size/offset wheels, if 24"s are all you can fit on it.
                   
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                  • sdh148

                    sdh148 Member

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                    I did my tire template clearance checks w/o torsion bars installed, so I could easily achieve max suspension jounce/rebound. For the jounce condition, I slightly compressed the jounce bumper to simulate a worst case condition. During "normal" driving, you will probably never see this condition combined with full lock steering.

                    However, when simulating larger diameter tires, I actually had a clearance issue with the suspension at a more normal height and with the tire turned only slightly. The outer "corner" of the tire would get very close to or touch the bottom corner of the front fender. I think this issue is more prevalent with lower profile tires. Tires with a higher profile/sidewall often have outer tread widths that are less than that of the same nominal width tire with a lower profile. In other words, a 225/60-15 tire may have a tread width that is smaller than a 225/35-18 tire, even though they are both 225 width. The skinnier outer tread width creates a less "square" tire profile and can increase clearance to the various components. Of course, there is also variation between tire brands/designs.

                    FYI, my 18x8 wheels have the same offset as the 1975 Dart 14" steelies that were originally part of the car from which I removed the front suspension/brakes to install on my '68.
                    https://www.summitracing.com/parts/RPM-TTR16-886550

                    I spent many hours analyzing and measuring before I bought my new wheels and tires, and this seemed to be the best package I could get that was guaranteed to fit under all conditions.
                     
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                    • kursplat

                      kursplat FABO Gold Member FABO Gold Member

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                      pics of the car?
                       
                    • 69_340_GTS

                      69_340_GTS Well-Known Member

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                      O.K., but the stock tires on a '69 Dart GTS were E70-14, which according to Coker Tire are 25.7" diameter x 8" section width. D70-14 were found on a Dart Swinger and they're 25.4" dia x 7.9" section. This size or a modern equivalent will fit.
                       
                    • sdh148

                      sdh148 Member

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                      Sorry it's so messy, but this is all I can do at the moment. The rear is supported on jackstands under the body and axle, so the amount of weight on the front of the car could be a little different than normal. 20200708_212640.jpg
                       
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                      • 273

                        273 Well-Known Member

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                        My uncle use to run 4.10 and swap to 3.23 anytime we went up to the cottage and swap back when got home. That's my plan since I could go my whole life without getting on the highway.
                         
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