Tyres: I have noticed an increase in correspondence in the various caravan forum recently that I follow that set me thinking about my approach to tyre maintenance. I tow a single axial caravan which, because of the corresponding high wheel loading is fitted with high pressure tyres that are noticeably stiffer than those fitted to our car.
Because of the lightweight construction of caravans and the complete lack of tactile feedback from a towed caravan the state of your caravan’s tyres need greater attention than those on your car. For those without TMPS the first warning of a problem with one’s caravan tyres is often a plume of black smoke visible in the rearview mirror, and that is rather too far past the point of no return for my liking.
Tyre Pressures: The recommended tyre pressures for your car and caravan will be found in their respective manual and on a sticker plate somewhere on the vehicle. That on the car will show a range of pressures depending on the load being carried. Calculating that load is where the difficulty starts for many of us.
I calculate the load for our car as follows:
Two people and one small dog = 180Kg
Caravan load on the tow-bar, I assume the maximum load for the car, in my case = 90Kg
Luggage ( I carry as much as possible in our car when towing) as weighed, say = 150Kg
So fully loaded we are under the maximum vehicle towing load of 2100Kg and close to being the same weight as four people in the car. In our case our fully ladened recommended tyre pressure is 37psi, and as we are a bit under that I inflate to 36psi.
I am fortunate insomuch that our car’s manufacturer recommends the same pressure for all four wheels and also the use of the higher pressure as a means of reducing fuel consumption when driving solo. This means that I don’t have to adjust pressures when unhitched and unloaded, lucky me!
Lunar recommend a tyre pressure for our caravan of 65psi. I have shown elsewhere that the loading on our caravan’s tyres is asymmetrical to a startling degree because all the heavy domestic fittings are installed on the off-side of our caravan. I have wondered if I should calculate the pressures for each side but so far have resisted the temptation and adopted Lunar’s recommended pressure for both wheels. The only indication I get of this uneven loading when towing is that the off-side tyre heats up more than the lighter loaded near-side tyre with a corresponding additional increase in pressure of several psi.
What about maintenance I hear you ask! It should not need saying that tyres should be regularly inspected for condition and pressure as part of your maintenance regime, but I will. Because of our TPMS tyre pressures on our rig are quickly displayed.
Tyre Age: Contrary to popular opinion there is no age limit on the use of tyres, their condition being the overriding factor when considering replacement. Car tyres normally wear their tread out well before any other problems become apparent, but that doesn’t usually apply to caravan tyres. The normal precursor for caravan tyre renewal is the appearance of small cracks in the side walls known as crazing. ROSPA publish a useful factsheet on this subject.
Hitch Weight: Conventional opinion with regard to your caravan’s hitch weight, is to load close to but not to exceed the vehicles maximum tow-bar weight whilst being careful also not to exceed the caravan maximum hitch load. The consensus being that heavier is better. There is also the oft repeated recommendation that the weight on the tow-bar should be between 5 to 7% of the caravan’s weight. In my case the tow-bar maximum is 90Kg while the caravans maximum hitch weight is 100Kg, so I load to around 80Kg, which just happens to be about 5% of the caravan’s maximum weight; how fortuitous.
Tyre Pressure Monitoring System: I’ve covered my choice of tyre pressure monitoring elsewhere. My chosen system gives me a real-time sequential read out of each tyre’s temperature and pressure as well as audible warning of any sudden changes in either of those parameters. It also illustrates the pressure changes that take place because of changes in ambient air temperature and that caused by operational loads. All of which I find both interesting and reassuring.
Tyre pressures are set for ambient air temperature, so will need adjusting when there is a significant change; I regard significant in this regard as about 5ºC. It is important to check tyre pressures “cold” in other words at ambient temperature before the vehicle is driven.
Tyre pressure changes with a change in temperature, a good estimate to use when comparing tyre pressure to air temperature is for every 5ºC temperature change, the tyre pressure will change by about 1 psi; so be prepared to adjust them to compensate.
A useful comparison table of temperatures and pressures may be found on Wikipedia.
May all your touring be puncture free.