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Customs What’s a good highway rear gear

Discussion in 'The Hokey Ass Message Board' started by ahshoe, Nov 24, 2025 at 5:03 PM.

  1. ahshoe
    Joined: Sep 12, 2012
    Posts: 1,052

    ahshoe
    Member

    Looking for a recommendation on a good cruising 65-70 mph highway rear gear for a 51 coupes I am working on. Has a mild Ford 302 with an AOD .What would be s good highway gear with that combination?
     
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  2. squirrel
    Joined: Sep 23, 2004
    Posts: 59,893

    squirrel
    Member

  3. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 15,920

    Bandit Billy
    ALLIANCE MEMBER

    3:70? I see Squirrel beat me to it.
     
  4. chevyfordman
    Joined: Oct 4, 2008
    Posts: 1,509

    chevyfordman
    Member

    definitely not the 3:55 with an AOD, I changed mine to a 3:70.
     
  5. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 15,920

    Bandit Billy
    ALLIANCE MEMBER

    I have a 3:55 behind a T-400 in my Olds, nice fit for around town and light highway use (<70).
    I have a 3:70 in the 41 PU behind a RE46 OD trans and it is a pleasure both in town and freeway speeds.
     
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  6. jimmy six
    Joined: Mar 21, 2006
    Posts: 17,047

    jimmy six
    ALLIANCE MEMBER

    If it’s in your avatar…I installed a 2.74 rear gear in our 56 and it’s perfect for hyway and street with no OD trans. I don’t know what the ratio is for your AOD or what rear you have and what’s available. Mine is an 8.8 from a Ford Explorer with F-150 drum brakes. IMG_2009.jpeg
     
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  7. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,258

    Mimilan
    Member

    Depends on Tyre rolling diameter.
    A good ratio for highway use would be between 3.2 and 3.4 depending on tyre size

    If it has 26" diameter tyres a 3.27:1 would cruise at 1981 rpm at 70mph in O/D
    pull it out of O/D for p***ing ,and the revs jump to 2958 rpm

    A 1951 Ford coupe weighs 3170 lbs [probably less with a SBF]
    And a Fox Body GT Auto Mustang weighs 3320 lbs
    This is a car of similar weight and a 302 [5.0] with AOD

    The GT Auto Mustang had a standard rear end ratio of 2.73 and a 3.27 ratio optional with auto trans
     
  8. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 15,920

    Bandit Billy
    ALLIANCE MEMBER

    All of the US (muscle cars, if you can call them that) had legs like that under them because they needed fuel economy, not for power or fun. Most of the late 70's Trans Ams I owned all had those gears, dogs on the street! Embarr***ingly so. Couldn't get out of their own way. They are cheap though, every wrecking yard has a host of 2 series carriers in them. I guess it depends on what the OP wants out of his ride. To each their own. Not every car needs to be quick. I get lousy gas mileage, but I make it from station to station in a hurry.
     
  9. krylon32
    Joined: Jan 29, 2006
    Posts: 10,874

    krylon32
    ALLIANCE MEMBER
    from Nebraska

    Another vote for 3.70's That's the ratio I sold most of when I built a customer ch***is with an OD trans.
     
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  10. Tow Truck Tom
    Joined: Jul 3, 2018
    Posts: 3,421

    Tow Truck Tom
    ALLIANCE MEMBER
    from Clayton DE

    @chevyfordman Seems to me that highway speed, these days, starts at seventy.
    jes sayin'
     
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  11. Dos Cincos
    Joined: May 13, 2011
    Posts: 935

    Dos Cincos
    Member

    I run a 3.50 gear with my mild 302 and AOD and it cruises just fine down the interstate
     
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  12. Tim
    Joined: Mar 2, 2001
    Posts: 20,195

    Tim
    Member
    from KCMO

    Tire diameter is going to be a big factor but given the general range of tire that would be common on a shoebox 3:70 sounds about right.

    There are plenty of free calculators online if you have a certain rpm at x speed you are wanting to aim for.
     
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  13. snoc653
    Joined: Dec 25, 2023
    Posts: 1,005

    snoc653
    Member
    from Iowa

    The answers given work for the people giving the advice. But you need more info to make a proper decision. Tire size, power and torque curve of the engine and all 4 gear ratios for the trans. And most importantly how you plan to drive it. There are numerous rpm calculators online. Once you have the above, figure out where you want it to cruise at the speed you desire. Also figure out what it looks like in each of the gears. If you accelerate you want to be somewhere in the power band and you want it to shift before you are out the top of that band. But you don’t want it to fall through the bottom when you hit the next gear. OD is usually a lock up gear so what does it take to lock it up?. Is 3rd a lock up also? Small blocks usually cruise at more rpm than a big block but with rpm comes exhaust noise. What is comfortable is also a consideration.
     
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  14. 38Chevy454
    Joined: Oct 19, 2001
    Posts: 6,782

    38Chevy454
    ALLIANCE MEMBER

    What type rearend are you running or have? That may help the gear ratio choice some. Also good point on tire diameter. I think around 3.55 will be good starting point for evaluation.
     
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  15. squirrel
    Joined: Sep 23, 2004
    Posts: 59,893

    squirrel
    Member

    keep in mind that the AOD might like to "hunt" between 3rd and 4th if you don't give it enough gear
     
  16. Nice Drivelines driveshaft. Wades white stripe.
     
  17. mixerman
    Joined: Jun 23, 2021
    Posts: 235

    mixerman
    Member

    I've got a 327 engine rpm 2900/ TH350/3:55 rear/28.9 dia. tire = 70.26 mph
    I wish I had around a 2.73 rear

    A good site to figure out what you have or what you need to get better results.

    Transmission Ratio RPM Calculator | ****er Parts
     
    Last edited: Nov 24, 2025 at 8:55 PM
  18. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 6,500

    57JoeFoMoPar
    Member

    65-70 will allow you run a little more gear. I like to gauge "left lane" speed, so I try to gauge my gear on an 80 mph cruising speed. I have a stock 3.08 rear with a 700R4 and a 27.7" tire, and it could really use a numerically higher gear. A 3.64 or 3.42 would probably be ideal, since right now 80 mph is 2000 rpm and sort of below the powerband.
     
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  19. AldeanFan
    Joined: Dec 12, 2014
    Posts: 1,170

    AldeanFan

    Something that starts with a 3.
    I have 3.45 gears in the ‘54 with a Yblock and AOD and it is a perfect cruiser with 205/65r15 tires.

    My mustang has a 302 and t5 with 373 gears and 235/60r15 tires. It’s also a great combo. It previously had 308 gears and that wasn’t enough, and 410’s temporarily but that was no good on the highway.
     
  20. ebfabman
    Joined: Mar 10, 2009
    Posts: 603

    ebfabman

    27 inch tall wheel, stockish sbc, 200-4r trans w lockup, and 3:73 rear gear. Perfect for a 1951 Merc.
     
  21. oldiron 440
    Joined: Dec 12, 2018
    Posts: 4,002

    oldiron 440
    Member

    3.73, I would think the 3.50 will having it in and out of OD on certain driving conditions.
     
  22. 49ratfink
    Joined: Feb 8, 2004
    Posts: 24,824

    49ratfink
    Member
    from California

    my OT car with OG 28" tall tires has a 3.42 gear. I do 2000 RPM's at 65 MPH. I don't see any reason to want a higher cruising RPM than that. the only time it downshifts is up a hill or when I hit the go pedal hard.
     
  23. DDDenny
    Joined: Feb 6, 2015
    Posts: 22,336

    DDDenny
    Member
    from oregon

    My 57 BelAir had a tired 283, T-10 and 4:11's, let them small blocks sing!
     
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  24. 1biggun
    Joined: Nov 13, 2019
    Posts: 930

    1biggun

    Id look at a 3.55 gear for a driver that see a lot of highway miles.
     
  25. I had an old hot-rodder (now I fit that bill) tell me years ago when I asked that question- 3.25 to 3.50 for non-OD transmissions, 3.55-3.90 for OD transmissions, and torquey engines such as Nailheads and straight 6s high 2s or low 3s
     
  26. Acres
    Joined: Dec 19, 2021
    Posts: 1,522

    Acres
    Member
    from Sweden

    My chevy with a tired sbc 267 with a 350 trans runs suprisingsly good with a 3.30 gear.
    But the most optimal choice is a high torque engine with a 2.73 gear, youll get there fast and cheap
     
  27. jimmy six
    Joined: Mar 21, 2006
    Posts: 17,047

    jimmy six
    ALLIANCE MEMBER

    They come to the house to measure and get the correct u-joints….how can you beat that!
     
  28. MARKDTN
    Joined: Feb 16, 2016
    Posts: 192

    MARKDTN

    An AOD has a .67 overdrive so take any ratio you had with non-OD and divide by .67. So if you liked 2.73s for cruising with a 1:1 transmission, with an AOD you could have a 4.1 to have the same RPM at highway speed. 3.73 is a common gear for an 8.8 or 9-inch as is 4.10. I would lean towards 3.73.
     
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  29. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 5,340

    ekimneirbo
    Member
    from Brooks Ky

    Get your tire size and use the calculator someone listed above to see what puts you at 80 mph and 2200/2300 rpms in overdrive. That is what it takes to be able to cruise with most traffic in my truck. I imagine my rear tires are probably slightly larger than what you will have. It came with 3.73 rear gears. What you don't want is to have to be at 2500 rpms+ when in the speed lane and just staying generally with the traffic. Try getting on an Xway and driving about 30 miles at 70 mph in your DD and see if you aren't constantly looking in your rear view mirror at the approaching traffic behind you........especially semis.
     
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  30. Plan on using a 3:70 in the wife’s car with an auto OD
    I have a 3:92 in the car I’m building with a 3 speed OD

    I cruise around 55 I’m my beater.
    Never an issue on the interstate
     
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