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Thread: Confused about tyre pressures now.....

  1. #1
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    Confused about tyre pressures now.....

    I didn't realise quite how much they changed when hot. My new TPMS has got me quite confused about what to set my preferences to now. I used to think between 28-32 PSI was good for me on corrugations & gravel tracks but having seen how 32 goes to 38 /39PSI when hot i'm not so sure I am getting things right anymore.

    Conversely when set cold at manufacturer's suggested settings I'm guessing they increase well above that.

    So, what are others doing in this regard?

    cheers

  2. #2
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    Reccomended pressures are ALWAYS cold inflation,this allows for the increase in pressure with heat.
    Andrew
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  3. #3
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    Smile

    Ozzy119


    From my understanding when you get the pressures right there should be around 4 psi difference from hot to cold
    I could be wrong tho


    Regards

  4. #4
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    I just installed a TPMS too. Only highway driving to date, but I've been starting as 36 psi cold. After an hour or so it's been getting to 39/40 which is in line with the 4 psi rule so I'm comfortable with that.

    On gravel and corrugations I'd be dropping the pressure, but also driving slower. That way the tyres don't heat up as much, and the pressure doesn't increase too much, and the 4 psi rule can still be met.

  5. #5
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    Quote Originally Posted by mechanic2you View Post
    Ozzy119 From my understanding when you get the pressures right there should be around 4 psi difference from hot to cold I could be wrong tho Regards
    I think you are right....but gee it's hard to get the difference to be only 4 psi as temps vary during the day, loads, speed, road conditions, etc.

    For me to get close to a 4 psi difference I need to keep increasing pressures and found at close to 50 psi achieves this, but ride is not flash.

    Brett.....

  6. #6
    Tombie Guest
    Kimberley Campers has a tyre guide and quote a "6 psi rule"

    Other rules - published by BSTG - never go over 40psi (cold)

  7. #7
    Tombie Guest
    For the record 5?c = ~1psi

  8. #8
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    It will also depend on how much weight you are carrying, the heavier the car, the more you put in, like mech2you.
    I use 36 to 38psi cold for the front, and depending on whether I'm loaded and towing the camper or just loaded without the camper, the range for the back is 40psi loaded without the camper, and 44/46psi with the camper. the front always stays the same.
    I then check these pressures at our first stop, if the increase is 4 to 6psi approx, then all good, if not, then I'll adjust my speed until I can reset the pressures accordingly, but so far these pressures have been good for me.

    Of coarse all this can change on really hot days

    My advice would be to keep trying different pressures until you get it right, good pressures are very important for the life and wear of your tyres.

    Baz.
    Cheers Baz.

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  9. #9
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    Quote Originally Posted by Tombie View Post
    Kimberley Campers has a tyre guide and quote a "6 psi rule"

    Other rules - published by BSTG - never go over 40psi (cold)
    I would agree with both those statements. The 4psi rule doesn't work with modern low profile tyres. From my experience, 6psi seems to be about right. I don't use it as a rule though as I just go by how the tyre feels - sometimes its more, sometimes its less, but not by much.

    Cheers,
    Jon

  10. #10
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    The one key issue in having a TPMS, apart from knowing before a tyre lets go, is that you now get to see how your tyres are performing in all conditions. We started testing TPMS just on 12 years ago and long before they were even heard of in Australia. In that amount of time and over all our tours we have collected an incredible amount of tyre performance data on most 4WD and tyres.

    So my first observation is you are seeing data for the first time so don't get overly worried. Set your tyre pressures to the recommended pressures and collect data as you drive in all normal conditions including towing and off-road if that is what you do. That then gives you a few things; firstly what "normal" is for specific pressures and driving conditions, then it tells you what temperature and pressure variations you get in each of those conditions.

    From there you simply need to look at if the tyre temperatures and pressures are increasing significantly in each of those driving conditions. If beyond around 6 psi or about 20C then increase pressures but no more than 2psi at a time. That way you can see if the temperature and pressures settle down and if they do then you now have got your "normal". BUT and it's a big one as you lower pressures for off roading for example that increases footprint which means higher resistance so higher pressures but at considerably lower speeds. Whereas if towing or carrying a heavy load your rear temperature and pressures will increase as a result of the load and higher levels of friction. In that situation we normally add 2-4 psi in the rears which seems to work pretty well.

    One more BUT. We recently tested a set of Cooper STMaxx which destroyed all our data as they behaved completely differently from every other tyre we have tested. We ended up running 50 psi in the rears whilst towing to stop the temperature and pressures keeping on going up. End result was an extremely hard ride that did not do us or the car any good at all. So what that means is sometimes all your data gets thrown out the window when you change tyres

    Have fun

    Rob

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