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Gears with 38.5" tires?

Discussion in '1982-Present GM Diesel' started by smprider112, Jun 17, 2004.

  1. smprider112

    smprider112 1/2 ton status

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    Gears with 38.5\" tires?

    I currently have 3.42 with 35x15.5x15 swampers....and my truck is a TURD!! its descent for town but if there is a hill it hates it! so Im thinking bout 4.10's BUT now I may wanna get 38's later down the road....will these gears be adaquate for this?? or should I possibly go to 4.56's? I'd hate to change out my gears then later get bigger tires and be back where i am now. Anybody running this combo with a 6.2? I need advise! /forums/images/graemlins/dunno.gif
     
  2. cegusman

    cegusman 3/4 ton status

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    Re: Gears with 38.5\" tires?

    I am running 4.88's with 39.5 boggers , wish I went with 5.13's
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Gears with 38.5\" tires?

    I run 4.56's with my 39.5" TSL's and I like it just fine. Could use overdrive for the freeway though.

    Rene
     
  4. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Re: Gears with 38.5\" tires?

    What transmission do you have?????

    I have 4.10's with 38" Swampers and in Drive it cruises pretty nice on the highway, but you cannot use O/D on the 700r4 because of the lack of power.......wish I had 5.13s
     
  5. eshorvath

    eshorvath 1/2 ton status

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    Re: Gears with 38.5\" tires?

    Are you wanting beter running than stock?
    Eddie
     
  6. mcinfantry

    mcinfantry 1/2 ton status

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    Re: Gears with 38.5\" tires?

    4.56 38.7 michelins and nv4500. im happy
     
  7. beater_k20

    beater_k20 Banned

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    Re: Gears with 38.5\" tires?

    i've got 4.56s and am going to run a 38.5-39.5 tire.

    ltalessi, what kind of Michelins do you run?
     
  8. k5 krawler 50

    k5 krawler 50 1/2 ton status

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    Re: Gears with 38.5\" tires?

    Not to hijack, but i have the 3.42 gears and plan on running 35x12.5 or 14.5 inch tires, rite now i have 33x12.5s and its turning about 2500 rpms at about 55 mphs, and i was wondering if it will be ok to run the 35s and not be sluggish up hills? It has a th350 that was built to handle 35s and about 500 hp do u think that will off set the gears in the axles a little bit so its not so sluggish? Sorry again to hijack, just wondering.
    Cory.
     
  9. k5 krawler 50

    k5 krawler 50 1/2 ton status

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    Re: Gears with 38.5\" tires?

    but i dont have the deseil motor any more either.. i have a sbc 400..
     
  10. mcinfantry

    mcinfantry 1/2 ton status

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    Re: Gears with 38.5\" tires?

    im running michelin 1100x16 xl's

    id like to add i do fine on highway with 105hp at 2300rpm and 286ftlbs torque at 1600rpm. the truck is no speed demon, but gets out of its own way. i get 22mpg in the city, 24 on the highway at 70. i SHOULD get 30mpg at a constant 55mph to 60mph.

    i just got back from LBL Ky and ran all the trails in 4wd lo 2nd gear at 650rpm. rear is locked, front was an unlocked ELECTRAC.

    3 days of wheeling burned 5 gallons diesel. the gassers burned 30-40 gallons.
     
  11. Steve_87K5

    Steve_87K5 1/2 ton status

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    Re: Gears with 38.5\" tires?

    Italessi, I've got a 4BT question...see new thread.
     
  12. mcinfantry

    mcinfantry 1/2 ton status

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    Re: Gears with 38.5\" tires?

    no counterbalance shaft. stock frito lay motor mounts.

    bowetieblazer on here went with me. hes going to put a 4bt in his after riding with me, (and i let him drive). i let tons of people drive at kentucky and converted 4 to cummins 4bt fans.

    it doesnt idle that bad and like i said works with my gears and tires just fine.
     
  13. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Gears with 38.5\" tires?

    [ QUOTE ]
    Not to hijack, but i have the 3.42 gears and plan on running 35x12.5 or 14.5 inch tires, rite now i have 33x12.5s and its turning about 2500 rpms at about 55 mphs, and i was wondering if it will be ok to run the 35s and not be sluggish up hills? It has a th350 that was built to handle 35s and about 500 hp do u think that will off set the gears in the axles a little bit so its not so sluggish? Sorry again to hijack, just wondering.
    Cory.

    [/ QUOTE ]

    If you're getting your numbers from a tach it needs to be re-calibrated. 3.42's, 33's, TH350 @55 mph you're spinning a hair under 2000 rpm. You're on the edge of roasting that tranny no matter how it's built. I'd run 4.10's at the least with the 35's.

    Rene
     
  14. k5 krawler 50

    k5 krawler 50 1/2 ton status

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    Re: Gears with 38.5\" tires?

    i already re-calibrated it once, cuz i thought it was off, but its not. So you think i am gonna blow up the tranny? I thought it might drop some rpms if i went to bigger tires?
     
  15. k5 krawler 50

    k5 krawler 50 1/2 ton status

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    Re: Gears with 38.5\" tires?

    I talked to the guy who built the tranny, and asked him about the gearing in it, and he said he put lower gears in it for the bigger tires. Do you think this is why i am turning a high rpm, with the 33s rite now? Thanks.
     
  16. kennyw

    kennyw N9PHW Premium Member

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    Re: Gears with 38.5\" tires?

    Rene, auto tranny's will always run slightly higher RPM's than the gear calculators say if they dont use a lock up converter. There is an efficiency loss in the torque converter since it can never reach a 100% power transfer with out the lockup device.
     
  17. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Gears with 38.5\" tires?

    I do know that Kenny. I don't rely on the online gear calcs out there...I do the math and input the numbers based on whether it's a manual tranny app, auto without lock-up or auto with lock up.

    55 x 3.42 x 355 / 33

    If it was a manual tranny or a lock-up auto you multiply by 336 instead of 355.

    Either you don't have 3.42's or your tach is off. The math doesn't lie. At 55 you are spinning 2023 rpm max with 33's.

    Rene
     
  18. Diesel Dan

    Diesel Dan 1/2 ton status

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    Re: Gears with 38.5\" tires?

    I ran 38.5 gumbos with 4.10s and it was a major slug. Truck was a '83 1 ton crewcab, NA 6.2 diesel with SM465/NP205. That much tire needs a turbo, IMO.
     
  19. k5 krawler 50

    k5 krawler 50 1/2 ton status

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    Re: Gears with 38.5\" tires?

    I know the tach is right because there are only 3 calibrater settings, ones for a 4 banger, one is for a 6, and the other is for an v8. So the calibration isnt off, and i am getting the rear end re built on tuesday, and i will ask the guy what gears are in it, but i am 90 percent sure that they are 3:42s, just because the card in the glove box says, and i know my uncle didnt change the gears, but i will find out on tuesday.
     
  20. kennyw

    kennyw N9PHW Premium Member

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    Re: Gears with 38.5\" tires?

    Cool, /forums/images/graemlins/thumb.gif Didnt know how you got your #'s and I didnt have the time to calculate anything myself. Sounds like you were way ahead of me then /forums/images/graemlins/doah.gif
     

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