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Thread: Mixing tyre sizes on RRC / P38 ?

  1. 13th April 2014, 10:12 PM #1
    superquag
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    Mixing tyre sizes on RRC / P38 ?

    This is all about the care and feeding of the BW's Viscious Coupling, keeping it relaxed and healthy... Same Transfer case in the last of the Classics, and the P38.

    Situation is:-

    Number One Son picked up 4 tyres and rims for a fantastic price, but one is stuffed. (cracked sidewall) BF Goodrich ATR 225/75-R16

    Idea now is to replace the front balding highway tyres on the Classic with a pair of these, which are half+ worn.
    Rear tyres are better than 70% 235/70-R16 Cooper ATRs.

    According to a tyre calculator, there's only 5 revolutions per km differance between the two (427 and 432 revs/km) In theory, there should be less now.


    Question is, 'Will civilisation end by having any such a size-differance'?

    - I can't see a quick aquisition of a s/hand 225 happening, which would solve everything. Plan D would be having the cracked one repaired properly, if possible.
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  2. 14th April 2014, 12:17 AM #2
    33chinacars
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    What's the Rolling Radius / Circumference. Run a tyre tape around them. IMO. If there is only 10 mm difference . It will be fine. Any more for short distance only. Otherwise you will start to get TC wind up & generating heat build up. Well that's my take on it. Sure others might disagree.
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  3. 14th April 2014, 01:00 AM #3
    superquag
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    Wot are you doing up so late at night/early in the morning ???

    According to this site Tyre Size Calculator

    the nominal differance is 27mm.
    - 2337 for the 225/75 and 2310 for the currently fitted 234/70.

    Actually, that's the obvious next step, - I'll nip around in the morning with a tape measure and get actual (differantly worn) dircumfrences.
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  4. 14th April 2014, 07:20 AM #4
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    bee utey
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    Once again, the "rolling diameter" of a tyre does not change with wear. It is a function of the steel belt length and is invariant with wear inless the tyre is massively overinflated and runs on tippy toes as it were. Tread block deformation occurs only under high dynamic forces.



    Stick to using the tyre specifications.
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  5. 14th April 2014, 10:07 AM #5
    superquag
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    Darn ! -Another cheap idea bites the dust...

    - Stick with your Day Job, 'cos you'll never make a good newspaper journalist. ('Never let facts get in the way of a Good Story') ...

    Edit: - plan B, now to find a similar s/h BFG A/T. Luckily they're still a current pattern. :-))
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  6. 14th April 2014, 03:26 PM #6
    Dougal
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    I've run 235/70 and 225/75 with an lt230 and no issues. But that's not a bw.
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  7. 15th April 2014, 02:05 AM #7
    33chinacars
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    Quote Originally Posted by superquag View Post
    Wot are you doing up so late at night/early in the morning ??? I'm a night owl

    According to this site Tyre Size Calculator

    the nominal differance is 27mm. That's a bit too much IMO
    - 2337 for the 225/75 and 2310 for the currently fitted 234/70.

    Actually, that's the obvious next step, - I'll nip around in the morning with a tape measure and get actual (differantly worn) dircumfrences.
    Next option

    Gary
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  8. 15th April 2014, 09:09 AM #8
    Dougal
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    To further Beeuteys points. My 225/75R16 have deeper tread than my 235/70R16. This brings their rolling radius even closer.

    I would have no issues running 235/70r16 and 225/75r16 on a BW if I had to.

    If you want to compare like for like, the BFG AT in 235/70r16 is 715 revs per mile: All-Terrain T/A KO | BFGoodrich Tires
    The 225/75R16 is 710 revs per mile: All-Terrain T/A KO | BFGoodrich Tires

    That's not even 1 percent difference.
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  9. 16th April 2014, 02:22 AM #9
    superquag
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    I am so tempted...

    Anyway, it's all become academic now, 'Sarah' has picked an argument with #1 son (current driver,,,,,) and is blowing a gasket or two. - Radiator is in the process of popping tanks off.

    Seeing as She's done over 180K I suppose it's to be expected.

    We may well end up with 4 rims for sale. Three-spoke 'Classic' and that greeny colour which looks a bit like the bluish 'Avalon'.
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