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Are 4.56 gears to low for 700r4 and 33" tires?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by shum1, Dec 5, 2000.

  1. shum1

    shum1 1/2 ton status

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    Are 4.56 gears to low for 700r4 and 33\" tires?

    I'm thinking everyone is sick of this question but here it goes. Currently I have 3.73's 31" tires no lift. I do fine on level ground but when I tow my boat in the mountians I have a hard time doing the speed limit, I want to avoid dropping into 2nd on the highway. I want to go up to 33" tires. I know I will need lower gears. If I go to 4.11 and 33's I will gain 100 rpm, not alot. If I go to 4.56 I gain about 400 rpm in 3rd while towing, too much? I do need more power. The best senario may have been 4.56 and 35's, I gain 200 rpm but there is no way my rig will fit in the garage with 6" lift and 35" tires, or even just 35's and 4" lift. Bottom line: 4.11 and 33's or 4.56 and 33's and I do live at 5000 feet so that comes into play also. The gear shop guys were reluctant to take my money for just moving to one gear step lower, go figure. Thanks.
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Are 4.56 gears to low for 700r4 and 33\" tires?

    I would go with the 4.56's if your towing. I don't blame the gear shop for not wanting to swap from 3.73 to 4.11, you would'nt notice much difference.
    Sounds like your garage needs a lift kit![​IMG]

    Rene

    [​IMG]
     
  3. Wheels

    Wheels 1/2 ton status

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    Re: Are 4.56 gears to low for 700r4 and 33\" tires?

    I looked into swapping out the TH350 in my 79 to a 700r4 and according to Dr 700R4 they recommend 4.11 to 4.56 gear ratio with 33" tires. Final drive ratio with 4.11 is 2.88:1 and 4.56 final drive ratio is 3.19:1. At 70 MPH 4.11 would run 2060 RPM at 70 mph and 4.56 would turn 2290 RPM at 70 MPH. With 3.73 gears and 33" tires at 70 MPH the RPM would be 1873. On 700R4, they recommend that you tow in 3rd and only shift to OD(4) on flat ground with light loads and if your towing heavy loads, stay in 3. Just passing on food for thought.
     
  4. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    Re: Are 4.56 gears to low for 700r4 and 33\" tires?

    If you are in 3rd when you tow go with the 4.56s. If you tow in 4th or even in 3rd on a lot of mountain roads I would go with 4.88s. Now that I have regeared I wish I had done it long ago. I have 4.56s and a TH350 with 35s. My buddy has 4.88s and a TH700R4 with 35s- when he tows he uses 3rd gear and it works great. Good up hill power and down hill control.

    Jim '80 GMC
    Freedom First!
    http://www.bigjbear.coloradok5.com
     
  5. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Re: Are 4.56 gears to low for 700r4 and 33\" tires?

    I'd go with the 4.56's, especially since you are towing. Also, as somebody already said, do not use overdrive for towing (unless it's a really light trailer).
     
  6. shum1

    shum1 1/2 ton status

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    Re: Are 4.56 gears to low for 700r4 and 33\" tires?

    Once again you guys made my decision easier. Thanks.
     

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