It is the air pressure inside the tyre that supports the load and therefore inflation pressures are dictated by the load upon the tyre. You will find the recommended tyre pressure for your motorhome in the owner’s manual. You should always adhere to the pressures given in your handbook.
Always check pressures when the tyre is cold as the pressure will rise rapidly after only a few miles due to the heat generated. Under-inflated tyres are a major concern, as they can overheat in operation and in the worst case scenario fail. Over inflation can cause a poor or unstable ride and uneven wear characteristics. Over inflated tyres are also more prone to impact damage as they are less able to absorb road shocks.
Generally, tyre pressures for caravans and trailers are higher than when the same tyre is used on a car, which reflects the higher load placed upon them. Motorhomes may have different axle loads from front to back and therefore the tyre pressure will need to be adjusted to suit, the chassis handbook should offer guidelines.Trailer wheels are normally smaller than those found on caravans and cars and often require higher pressures to enable them to support the weight on the axle.
If the required tyre pressure exceeds 60psi then a higher specification valve will be needed (most commonly one with a metal stem and high pressure valve cap). It is important to tell the supplier of a new tyre the operating pressure so the correct valve is fitted.
Car manufacturers often advise raising tyre pressures when carrying a full load, particularly on the rear axle. Large SUV-type vehicles may not need a significant tyre pressure change when towing but more conventional cars may well need an increase as the load on the hitch can be quite significant. This information should be on the car somewhere (see below).
If you are unsure what pressures your car tyres should be, contact the tyre or vehicle manufacturer. In the absence of any specific tyre pressure recommendations for towing, inflate the rear axle tyres to between four to seven psi above the maximum specified in the vehicle handbook, however do not exceed the tyre’s maximum inflation limit, identified on the sidewall of the tyre.
If you intend towing at the higher speed limits permitted abroad then you may need to adjust the tyre pressures on your unit and reduce the tyre loading (see Load and speed section, page 2). If in doubt, check with your trailer manufacturer or tyre specialist.