Tyre pressures for van conversions.

kevjan wrote:I have weight my van on a couple off occasions and always around 3400 kg which I suspect most van conversion and coach build would be on a 3500kg chassis. I used to run my tyres at 70psi all round but have dropped them to 65psi it made a big improvement to the ride and am thinking about dropping to 60psi all round to see what that is like. This is only my thoughts but each to there own. Kevin

The individual axle masses determine the front and rear tyre pressures, not the overall mass of the vehicle.  The type and size of tyre also determine the pressures.

kevjan wrote:I bet there is no one with camper/ Motorhome that’s willing to weigh there individual axial every time they use there van that’s the only way you would ever get it exactly right so you have to use an average. Kevin

Of course not.  Most of us load up the van for a trip as you did when you measured your overall mass at 3400 kg and then measure the axle masses.  You are right, they will be different every time you use the van but the aim is to measure the worst case i.e. maximum axle masses that you are likely to have.  If you feed these masses into TyreSafe's on-line calculator it will give you the ETRTO pressures for an axle mass that is 10% higher.  This additional 10% is to compensate for uneven loading across the axle and small increases in axle mass.  It's OK to be slightly overinflated but not to be under inflated.  The air in the tyre represented by its pressure is what supports the tyre's load, not the tyre itself.  If the tyre is under inflated the tyre wall will try to support the load and overheat in the process leading to a risk of a blowout.  Tyre wear and handling will also be impaired.

kevjan wrote:Yes exactly it’s not possible to work out different pressures every time you use the van so you find a decent pressure that suits you. The same with a 44 ton truck never run at same weight but tyre pressure is the same whether empty at approximately 18000 kgs or fully loaded at 44000 kgs always same tyre pressure. Kevin

Kevin - you are correct but the "decent pressure that suits you" should be the ETRTO pressure for the maximum axle mass you are likely to have plus say 10% as per the TyreSafe model.  In this way your pressure will either be spot on (unlikely) or slightly high depending on the load you are actually carrying which will vary a bit trip to trip.  What you shouldn't do is establish a high and low figure for each axle mass and then set the pressure for the mean value.  If you do that your tyres will at times be under inflated.