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Thread: Warranty after changing to Michelin PSS4

  1. #31


    Thanks Blueraven & Kais3r for your additional feedback.

    As it seems the 245m wide tyre clearance to rear guards is not an issue, I will seriously consider going to 245/35 all round. Tyre wall height will also increase slightly with this combo, but hopefully not enough to feel noticeably softer.

    Regarding the Haldex unit & effect of varying tyre diameters, it will need to allow additional slip through it's clutch pack hence possibly increasing oil contamination & filter blockage.



  2. #32


    Thank you all.
    How does it go being under the placard if you have an accident?
    ive kept the half worn 235 MPS4S rears and put new 4S 255's on the front on the basis that the front / rear rolling circumferences are now, theoretically at least, within less than a third of one percent of each other. Intend to experiment by keeping 5psi between front and back to see how it goes. Will try and actually measure them.

  3. #33


    Not sure about the rules for other states but in Qld,

    The maximum tyre width for a car or car derivative must not be more than 1.3 times the vehicle manufacturer’s widest optional tyre.


    A passenger car, passenger car derivative or ‘soft roader’ (an all-wheel drive vehicle other than MC category), the overall diameter of any alternate tyre fitted may be up to 15mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

    As far as your tyre combo goes, new 255/30/19 front PS4S and half worn rear 235/35/19 PS4S tyres, fronts would be 0.8% smaller, with 1% height difference equating to approx 3mm in tyre wall height difference (not overall diameter) the rear tyres should be deflated to suit, but be careful not to lose too much psi to get there due to handling characteristics and accelerated outer edges tyre wear.

    A temporary solution but in future it’d be best to get matching diameter tyres within 0.3%, preferably the fronts being the fractionally larger if necessary.

    With measuring tyre wall height off the ground, it’s not an exact method either as front vs rear wheel camber can affect readings, making the front tyres look bigger than they are, measuring the inside and outside and averaging the difference could get you a close enough true reading, but the ultimate way would be to do a rolling test over a set distance, this will be much more accurate and exclude any need to compensate for other factors.

    You can do this for example by:

    Find a stretch of flat bitumen (driveway may suit if it has 10m of level concrete)
    Get someone to spot for you.
    What you want to do is create at least 8m of driving space in front of your car, then chalk your front and rear tyre down the vertical centre on the side wall as close to the tread as possible, mark the “ground” at the front wheel in line with the chalked tyre too, then measure 7m from the ground mark towards the front of the car (straight driving line).
    Drive forward so the front tyre reaches the 7m mark, you want to get the front tyre chalk mark back in its original position (middle bottom) either within a foot before the 7m mark or the next time chance you get after the 7m mark.
    Check your chalk marks on the tyres, they will be out from one another, mark a new centre on the rear tyre and measure the circumference around the tyre tread between the two marks, if it measures less than 20mm then you’re tyres are less than 0.3% out from one another which is close enough.

    Adjust tyre pressures to get within that margin and retest.

    Silverrsthree, For your particular circumstances, if your tyres are equally pressurised right now, measure the rear sidewall height now and then drop the PSI till it’s 2.5-3mm less, then do the test and it may be within the 20mm margin.

    In comparison PS4S new all round 255/30/19 front and 235/35/19 rear, all inflated the same PSI, the marks would be out by 125mm over approx 7m of travel (1.8%).

    Get it as close as you like of course but 20mm is fine.

  4. #34


    Except for leaving the tyre shop, no traction action over 100kms today.
    Thanks for the pics Javbomb. I think I like your solution best.

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