Tyre Pressures

Oct 28, 2016
Hello, I'm sorry if this has been asked before. I take the wheels off my caravan for the winter, I'm about to put them back on for my first trip away. Before I put them on I take them to a garage and check the pressures. However I am now thinking I should check the pressures with the wheels on the van as the pressure will increase with the weight of the van. What are peoples thoughts on this?
Nov 11, 2009
My tyre dealer inflates the tyres off of the caravan or car and then fits them.
The contact area increase under load is relatively small and makes little difference to the pressure that they were inflated too prior to being balanced and then fitted. The link below may help understand.

The maths relate to a 1000 kg car with a weight increase of 500kg. But with caravan tyres being at higher pressures and stiffer sidewalls I would not expect much change. Why not recheck your tyres when fitted to the caravan to see what change is measured. The van need not be fully loaded as 150-180kg payload will not make any significant difference to the contact area.
Mar 14, 2005
Fundamentally its about the tyres contact area with the road. Tyre manufactures will have worked out what is the best compromise between contact area and rolling resistances for each tyre they produce. From that they will recommend inflation pressures based on the load the tyre is expected to carry.

For any given tyre inflated to a pressure, when it is loaded the tyre will deform until enough area of the tread is in contact with the road that it supports the load. There are a number of factors that will affect the result to a some degree but in simple terms Contact Area x Pressure = Load.

Because of the shape of a tyre if you load it more heavily the tyre presses closer and more tread comes into contact with the ground, but the volume only changes by a much smaller amount. Consequently the internal pressure changes very little when loads increase and in practice is ignored. but extra load increases the contact area and the amount of tyre wall that is deflected. This will increase the rolling resistance, and is also likely to increase the tyres self heating effect which may be enough to damage the or weaken the tyres integrity. So to bring these things back into normal range, they will suggest raising the pressure to move back towards the preferred contact area.

When driving tyres are subjected to a very wide range of loads. These are usually transients and on average will tend to cancel out. Tyres are designed with these transients in mind so they can usually handle small shifts in static loads with no obvious problems, but over time, shifts in the average pressures either above or below the recommended pressure for a given load will affect tyre wear, and vehicle efficiency.
Nov 16, 2015
Hi Paul, I have just fitted A Tyre Pal, pressure monitor to my caravan, and was surprised at the resulting pressures, The tyre pressure recommended is 65 psi. So I set the tyres, using my pressure gauge, and on setting up the unit, this agreed to my gauge. Towing the van back to storage today, a distance of about 12 miles, the pressures increased to 73 psi, and the temperatures went from 9c upto 16 c. during the trip.


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