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Thread: Change rim size

  1. #21
    Join Date
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    Default Re: Change rim size

    Just for interest sake:
    I went from 265/75R16 to a 31"/10.5R15

    Size 1 Size 2
    Diameter
    803 787 -1.9%


    Width
    265 267 +1%


    Sidewall
    198 203 +2.6%


    Circum.
    2525 2471 -1.9%


    Revs/km
    396 405 9

    As stated above i did however have to put a 30mm spacer on to clear the brake calliper.
    05 Mitsubishi Pajero LWB 3.2 Did GLX
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  2. #22
    Join Date
    Oct 2009
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    Default Re: Change rim size

    Quote Originally Posted by jelo View Post
    No it is NOT

    31" is 31", there is no difference in the tyre diameter. Hence no difference in the rolling circumference nor the speed, the torque, the power or even the odo and speedo reading.

    A 15" rim with a 35x10.5x15 tyre will have the same speed and odo and everything else as a 35x10.5x16 tyre on a 16" rim.

    If you can't follow this, stay with a standard rim and tyre please.
    Now that we have a vague idea how tyres work, I have to throw a spanner in the works...

    A 31 is not quite a 31. Same for e.g. a 265x70R16.
    A 31x10.5R15 BFG AT WILL have a different circumference than a 31x10.5R15 BFG MT.
    The same, a 265x70R16 Cooper AT3 WILL have a different circumference than a 265x70R16 Cooper St Maxx.
    We are not even gonna try and compare 'the same size' Conti with a GoodYear!

    All the spec sheets are on the internet. Download and check for yourself.

    Now, the differences between the "same size" tyres are negligible when it comes to power and consumption, but using a mix at the same time on the same vehicle will kill your drivetrain.
    All your diffs will have issues, including your centre diff. Even worse if you have locking diffs. Lots of pics on the internet of split difff casings. Limited slip diffs will overheat severely too.
    This is also why you always replace all the tyres on a 4x4 or AWD at the same time.

    This is something tyre calculators will not tell you, because they work on perfect-world, theoretical calculations.
    Last edited by RogueFrontier; 2018/07/12 at 07:09 PM.
    -----------------------------
    Isuzu Frontier 280LX 4x4 2001

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  4. #23
    Join Date
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    Default Re: Change rim size

    Also important to rotate your spare/spares regularly to keep all 5 or 6 tyres evenly worn. On directional tyres, also include a swop from side to side. I know this is a pain to have the tyres turned around on the rims, but, particularly on an IFS vehicle it helps to keep your set evenly worn. I see too many people with "display" polished tyres on the spare wheel carrier, and the wheels on the road are at 50%. You may think you are saving some money now, but the day your wife gets a flat, and the AA guy shoves that new tyre on the rear end, and you end up with diff failure, you will wish you just worked that R3k piece of rubber into your rotation schedule.
    David/Hillbilly - 1997 SFA Nissan Sani 2,7 TD - 5" lift on 33" tires - Dual Transfer with 4.1 gears

    http://www.youtube.com/user/davidabcab



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