Tyre Pressure - Too High or Too Low?

Discussion in 'Tech/Mech General' started by Robert Clark, Nov 21, 2015.

  1. Robert Clark

    Robert Clark Funster Life Member

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    The recommended tyre pressures for my MH (according to the Manufacturer) are 5.5 bar front and rear, based on the tyre size that I have

    The max tyre pressure written on the tyre is 5.5 bar

    The dealer suggests 3.4 - 3.8 bar for the front and 4.1 to 4.5 bar for the rear, as they feel that the ride is a too 'hard' otherwise.

    I understand that low tyre pressure can affect handling and fuel consumption

    Who is right, the dealer or the manufacturer?
     
  2. MyDogsTooBig

    MyDogsTooBig

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    Manufacturer. But depends upon laden weight also. It should not deviate that much. 0.5 bar less for front is normally okay with high pressures. Tyres too low will mean extra heat and more chance of blowing out. It also stresses the side wall more, because there is more flexing, less stability because the vehicle is moving more on the tyre, more chance of damage. I am sure there will be contradictions coming though...
     
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  3. Robert Clark

    Robert Clark Funster Life Member

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    Would the lower pressure affect steering and handling too?
     
  4. Zigisla

    Zigisla Funster

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    Manufacturer. Dealer probably has the experience of running the vehicle at those px but the manufacturers have the tech knowledge for the weights etc.
     
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  5. Stealaway

    Stealaway Funster

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    I would trust any motor home dealers.
    For all the money we spend with them for 'expert service and advise' they still seem to be a bloody cottage industry.

    Its good job we can depend on expert advice from forum members that have genuine knowledge of motor homes.
     
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  6. MyDogsTooBig

    MyDogsTooBig

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    The front is more susceptible to incorrect tyre pressures. Low tyres will help it track straight, so steering is dulled down (less wander or wobble with undulations and wind), but that then makes turning more difficult, because it will want to keep straight. For the backs, the turning effect is less of an issue, but it is usually where most of the weight is. Low tyres for the backs will reduce harsh bounce and reduce wander in winds. The problem is, that because the weight is in the back, low tyres at the back will increase tyre wear and stresses and generate more heat, which is not what you want. Tyre wall maximum pressures are just that and are a guide. You should however be near the guide, not nearly half of it. I adjusted my rears depending upon weight, but only by 0.5 bar. If you are tactile, you will feel what is not good with tyre pressures and be able to adjust them. If you have a lot of sway and weight at the back, then air bags give good correction and are easily adjusted by air pressure for differing loads weights, which is what I did when carrying water when I had no choice. If your steering is twitchy and you have to correct it a lot as you drive, then a lower tyre pressure will correct this to an extent, but only go down a small amount in pressure. If the problem persists, then check toe in/out and/or think of fitting a steering damper.
     
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  7. John Laidler

    John Laidler Funster

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    What tyres have you got? The only way to really find what pressure they should be at is to ask the tyre manufacturer, not the vehicle manufacturer or the dealer.

    In order to find the right pressure you will to take the laden MH to a weighbridge and determine the axle weights.

    If you have Continental tyres there are charts you can look up. I now run my tyres at a much lower pressure than the vehicle handbook says but the pressures are spot on by Continental and the ride is much better.
     
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  8. Robert Clark

    Robert Clark Funster Life Member

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    Continental VancoCamper 225/75 16 CP

    Do you have a link to the suggested inflation pressures ?

    Thanks
     
  9. DavidG58

    DavidG58 Funster

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    No technical skill on my part, but I would not be comfortable running the tyres at the maximum recommended pressure :), always like to see some margin (y)
     
  10. funflair

    funflair Funster Life Member

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    I would go with the dealers figures, max pressure would go with max load.

    Martin
     
  11. TheCaller

    TheCaller Funster

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  12. John Laidler

    John Laidler Funster

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  13. Clarky

    Clarky Funster

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    @Robert. Get the van weighed if you haven't already and then email Continental with the tyre type and size and loaded weights for front and rear axles.

    www.continental-tyres.co.uk for more info.

    They will give you the correct pressures.

    Not sure which van you have but I've recently emailed Michelin for my pressures and have been told to keep 80psi in the rear and 51psi front.
    That's for a Carthago Chic C-Line with a max weight of 4500kg.

    Richard.
     
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  14. Southampton

    Southampton Funster Life Member

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    I have tyrepal on my tag axle and when I set the rears to 70psi (Michelin Agilis) when they get up to temperature on a run the pressure goes up to about 80psi, when in Spain last year they got up to 85 psi. It's a similar ratio with the fronts. The tyre temps are not excessive maybe 30-35 ish dregs. .......so......when the manufacturers/dealers say to set them to 80psi does this take into account the running pressures??? Or does it not matter?...

    I should say this is on a warm day for both temp and pressure.
     
  15. Robert Clark

    Robert Clark Funster Life Member

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    Hi Richard - I've got the exact same van as you.
    Will get it weighed when loaded up and contact Contental
     
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  16. Robert Clark

    Robert Clark Funster Life Member

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    Everywhere I've read, tyre pressures are given for COLD tyres, which therefore must take into account the fact that they get hotter when travelling
     
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  17. John Laidler

    John Laidler Funster

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    I think this is it. Your tyres are on pages 80 and 81. It is a bit hard to read as you need to look at both pages at the same time!
     

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  18. Robert Clark

    Robert Clark Funster Life Member

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    Thank you very much!
    Just need to find a weigh bridge now
     
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  19. Robert Clark

    Robert Clark Funster Life Member

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  20. Robert Clark

    Robert Clark Funster Life Member

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    On further investigation I've discovered that the dealer may have deflated my tyres a bit too much as they are currently below even their own 'preferred' figures by about 10psi
    I'm going to re inflate them, then to go a weighbridge, to confirm the correct pressure according to Continental
    I'm also going to get the wheel alignment checked - recommended annually, as we've been driving on some terrible roads in Italy and hit loads of pot holes.
    Hopefully we'll then be set for our next trip in December
     
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