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Thread: Diff Ratio Change to 5.13 from 4.625

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    Diff Ratio Change to 5.13 from 4.625

    Hi,

    I have recently changed out my standard GU/ST 2.8TD 1999 Wagon 4.625 diffs with 5.13 ratio diffs, I am very happy but am currently running 265/70 R16 Goodrich tyres that are due for replacement, I was waiting for them to wear out before i went for larger diameter tyres.

    Has anybody done this diff ratio change or can direct me to any tables that give some ratio/tyre size information or even what tyres you fitted if you,ve done the mod.

    Brgds/Ian

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    G’day Ian Mate,
    As a rough rule of thumb I believe Patrol 5% is a fair guesstimate gear swap ratio/tyre gauge:
    Differentials- 3.9 <> 4.1 (5%) / 4.1 <>4.3 (5%) 4.3 <>4.6 (5%) etc….
    In regards tyre diameters my noggin only comprehends imperial sizes:
    31” <> 33” (5%) / 33” <> 35” (5%) etc….


    Sent from my iPhone using Tapatalk

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    MudRunnerTD (26th November 2021)

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    Everything that MB said. The diff ratio that you have gone for i have not heard of before? What did they come in? going from 4.6s to 5.1s is about a 10% increase (About 2 ratios up). Common to go to 4.6s in TD42 to turn 35s and or 37s and the 4.6s out of the RD28 are well sort after.

    Your 265s are about a 30.6" so called a 31" factory tyre.

    Check this calculator for research

    https://tiresize.com/tyre-size-calculator/

    For your information to make the tyre size make sense this is how it is broken down.

    265 (Width of the tread)
    70 (Tyre Wall height as a % of the tread width - ie. 70% of 265 = 185.5mm wall height)
    16. (Rim size)

    I would expect you to turn 35s easily (315/70R16)
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    I like this one. Just got a tape and measured my tire height in inches and chucked that in as metric tires are all a little different even when the numbers are the same.
    https://www.marks4wd.com/gear-calculator

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    Dif ratio change and low range reduction are on my dream list.
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    Diff ratio Change

    Dear MB,
    I
    Sincere appologies for the late reply, I just found your email in my spam box, I had thought I hadn,t got any replies.

    Thanks for the note, I have been doing the calculations and roughly I have made a 9% diff ratio change ..... (thats 2 ratio steps from the typical options avail) I decided to go for the big change and am very happy I did, such a great driver around town now and absolutely epic in the bush so I have no regrets however if i do long road trips (with no offroading planned) the increase infuel burn becomes an issue ( I had originally planned to go bigger wheels with the ratio change to go with my 2" lift but was so happy with the truck with the ratio change I have been in no hurry.

    I have been looking at whats out there tyre wise and by current tyre size is 265/70 R16 (30.6" dia) so I roughly worked out the following now:

    285/75 (32.8" dia) a 2.2" taller overall dia being about a 7% change
    275/70 (31.2" dia) a .6" taller overall dia being about a 2% change
    265/75 (31.6" dia) a 1.0" taller overall dia being about a 3% change


    Therefore the 285/75 is approx .8" wider than I have now and 2.2" in diameter bigger (IE: 1.1" lift) so overall this size seems to be the most obvious choice for long road trips without loosing my full 9% change and more likely will be my choice if just looking to improve fuel burn on long trips however the 265/75 might be a step better in burn but keep closer to the ratio i am enjoying ....... in the end it might end up being 2 sets of wheels.

    All very interesting but once I got into the revolutions/mile of tyres my head got dizzy so like most things it might end up just being a bit of trial n error.

    Brgds/Ian


    G’day Ian Mate,
    As a rough rule of thumb I believe Patrol 5% is a fair guesstimate gear swap ratio/tyre gauge:
    Differentials- 3.9 <> 4.1 (5%) / 4.1 <>4.3 (5%) 4.3 <>4.6 (5%) etc….
    In regards tyre diameters my noggin only comprehends imperial sizes:
    31” <> 33” (5%) / 33” <> 35” (5%) etc….


    Sent from my iPhone using Tapatalk[/QUOTE]

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    Thanks MD and also sorry for slow reply to this thread , (have a read of my reply to MB above for my findings so far) and to answer question on why 2 steps on ratio change I looked at what Superior Engineering had to offer and I decided to go 2 steps as the standard ratio was just a joke and unless in 4x4 low conditions the driving anround towns was a pain in the arse...... I spoke with the engineering company in Taren point who also agreed that if I went 1 step up and I didn,t like the improvement its an expensive gamble so went 2 steps and (for me) it was the right way to go.... but as my above reply to MB .... its just long distance drives across the outback where 4x4 high is typical the the larger size tyres make more sense just for fuel burn reasons ..... however closer to home I would not change the current gearing/tyre compination.

    Brgds/Ian



    Quote Originally Posted by MudRunnerTD View Post
    Everything that MB said. The diff ratio that you have gone for i have not heard of before? What did they come in? going from 4.6s to 5.1s is about a 10% increase (About 2 ratios up). Common to go to 4.6s in TD42 to turn 35s and or 37s and the 4.6s out of the RD28 are well sort after.

    Your 265s are about a 30.6" so called a 31" factory tyre.

    Check this calculator for research

    https://tiresize.com/tyre-size-calculator/

    For your information to make the tyre size make sense this is how it is broken down.

    265 (Width of the tread)
    70 (Tyre Wall height as a % of the tread width - ie. 70% of 265 = 185.5mm wall height)
    16. (Rim size)

    I would expect you to turn 35s easily (315/70R16)

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    MudRunnerTD (10th December 2021)

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    Excellent but sadly doesn,t cover my Patrol 2.8TD

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    I used your chart and simply transposed the gearbox for a 3.0 litre 5 speed manual (closest to my 2.8TD 5 speed manual) and by the looks my choice of 285/75 would get me very close to original gearing. Thanks again.

  13. The Following User Says Thank You to Engism For This Useful Post:

    MudRunnerTD (10th December 2021)

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