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Difference between 4.88's and 5.13's

Discussion in 'The Garage' started by odoa3, Mar 23, 2007.

  1. odoa3

    odoa3 1/2 ton status

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    Sorry, another gearing thread. I have a '75 K5 350/th350/203 with one ton running gear, spool in the 14 bolt, and a Detroit waiting to go into the 60. I am running 35 inch Boggers, but will eventually be going to 38.5's. I currently have 4.10's. This only sees the road on the way to the trail, no highway running.

    I am trying to decide between 4.88's and 5.13's. I would really like to go with 5.13's if I can. Using this gear calculator http://www.grimmjeeper.com/gears.html I have ran both and found that I will be turning 3000 RPMs at 58 mph with 5.13's. I don't feel super comfortable doing anything over 55 anyways with this truck so no worry there. However, I am somewhat concerned about turning 3000 rpms for the run to the trail and home.

    If I go with 4.88's will I be sorry down the road when I go 38's? For the cost of the gears and time to install I only want too have to do this once.
    A trailer would be nice, but with the cost of trailers up here, that just is not in the cards.

    Sorry for the book, and I appreciate any help or recommendations you guys who have ran these gears can give me.
     
  2. thebird00

    thebird00 1/2 ton status

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    I'm running 39.5 boggers with 5.13s, but I have overdrive too. I don't have any experience with the 4.88s, but I think thats what you would want if you are gonna be seeing any highway driving with the th350. I'm running a stock 350 and feel like I have enough power. If you have a mild built 350 I think you'll be fine with the 4.88s
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    If it were me i would go 5.13's since you plan on going with a 38" tire in the future. 3000 rpm's won't hurt a thing except some gas mileage and you said you won't need the highway anyhow. Too much money to swap from 4.88's to 5.13's down the road if you don't end up happy with 4.88's and decide to change later. Just do it now and don't look back.
     
  4. 8_YOUR_H2

    8_YOUR_H2 1/2 ton status

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    I really don't think you will be able to tell that much of a difference between the two on the trail or on the road with a 3 speed automatic transmission. I had 4.88's and 38" tires on my K5 and drive it to and from the trail with no issues. If there is a huge difference between prices then go with what ever is cheaper otherwise go 5.13 so you don't have to worry about doing it again in the future if you get a bigger tire.
     
  5. sledheadak

    sledheadak 1/2 ton status GMOTM Winner

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    go with the 5.13s for the 5th or 6th time
     
  6. cegusman

    cegusman 3/4 ton status

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    I have 4.88 and wish I went with 5.13 instead.
     
  7. DaPlumber

    DaPlumber 1/2 ton status

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    5.13's Just Do It!!!!!

    IMGP0062_resize.JPG
     
  8. SkysTheLimit

    SkysTheLimit 1/2 ton status

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    Don't fear the gear! Go 5.13! I'll be going 5.86 when I swap in my 1 tons. One of the perks of running a D70HD rear instead of a 14 bolt... My target tire size is around 38-40". Granted, I do have overdrive for those long hauls on the highway but you said you don't care to do over 55 anyway.
     
  9. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Exactly 0.25 :D Couldn't resist :wink1:
     
  10. odoa3

    odoa3 1/2 ton status

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    Thanks guys. I guess 5.13's it is . Man, I wish I had a trailer. Guess I will be just a little slower getting to the trailhead, but no biggy.

    Thanks for the help.
     
  11. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Swap out your 203 box for either a STaK 5.44:1 box or an Atlas4 5.44:1 box..... and keep the 4.10s

    You will have a great crawl ratio, and your highway RPMs will still be nice and low.


    If you want the details (crawl, highway RPM calcs, etc) just post up and ask. I'm doing an Atlas4 with my K5 and I'm keeping my 4.10s and running a 39" tire.

    It's a better solution than 5.13s or 4.88s for people without an OD tranny.


    :usaflag:
     
  12. 8_YOUR_H2

    8_YOUR_H2 1/2 ton status

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    I guess if money was no option.......
     
  13. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    "object"?? :wink1:




    I was careful not to say that it was the cheapest solution, but it is a SUPERIOR solution. Let's take a look at the numbers:



    Option 1: - Re-Gear to 5.13s

    Crawl Ratio = 1st Gear (5.04 w/stall) X NP203 (2.01) X Axle Gears (5.13) = 51.96:1

    Highway Driving @ 65MPH = 2873 RPM (39" tire)
    Highway Driving @ 65MPH = 3201 RPM (35" tire)


    (or)


    Option 2: - Replace 203 Box with STaK or Atlas and keep existing 4.10s

    Crawl Ratio = 1st Gear (5.04 w/stall) X STaK (5.44) X Axle Gears (4.10) = 112.41:1

    Highway Driving @ 65MPH = 2296 RPM (39" tire)
    Highway Driving @ 65MPH = 2558 RPM (35" tire)


    Personally, spending the money to do two complete gear swaps to only achieve a 52:1 crawl ratio is a complete waste of money....Plus, you get the added penalty of a vehicle that is almost undriveable on the highway and drinks fuel like it's still 30-cents a gallon!!! :yikes:

    A deeper reduction box is simply a BETTER solution for anyone with a non-OD tranny that still wants a dual-purpose rig. 5.13's alone are not going to solve this guy's problems.....


    :usaflag:
     

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