I recently read a question from a Class-A motorhome owner about the need for carrying your own air compressor. My thoughts and reply to the question:
run the 10% extra pressure (above the minimum required to support the
actual tire load) I and others suggest, and if you keep an eye on your
pressure every travel day with your TPMS, you should get plenty of
warning on when you will need to add air. While +/- a couple psi is
normal for temperature variation, if you see a 5% loss one day and
another couple the next, etc., then that should be a warning that you have a
leak, which indicates some problem that needs to be addressed sooner
rather than later. Once you see -5%, simply stop at the next fuel stop
and use the high pressure that is available at truck stops.
People need to remember that it is normal for tires to lose between 1% and 2% of their inflation pressure each month (adjusting for temperature and barometric pressure variation). This is the result of the molecules of air moving out between the spaces between rubber molecules. I also
note the concern about most small compressors not being able to inflate a
large tire that has lost a lot of air.
If you have lost sufficient air
to be more than 10% below what is needed to support the load, you really
do have a problem that more than likely needs professional service, not
simply a "top off" of air. If you have lost 20% or more, you should not
be driving on that tire and also should not be inflating your tire outside a service center tire safety cage, as
running a tire very low may have damaged the steel body cords to the
point that the tire might explode when being inflated and result in injury.
I also read a question about running the exact air pressure needed to support the tire load. Following this practice creates a couple problems:
1. Every time the temperature changes 10°F, your pressure will also change about 2%, which could mean you would be running your tires under-inflated. Not a real big deal, but every mile of operation in overload may consume part of the tire life with the potential of having an early failure.
2. I believe that you would soon tire of constantly adjusting your tire pressure up or down one or two psi every day. When you get tired of this constant effort, I am afraid there may be a tendency to forgo checking and adjusting the air. This could lead to a failure when you go an extended time without checking your pressure. This is why I suggest the 10% margin.
Of course this raises the question from some about increased inflation causing hard ride. Now, running higher pressure could lead to a harder ride, but while I believe that running more air than the minimum needed to support the load may
theoretically contribute to a harsher ride, I doubt that there are many
riding in Class-A RVs who can feel a 5 psi or maybe even a 10 psi
difference in a controlled blind test. This 5% or 10% translates to a 1
to 3 psi difference in a car, and I have seen many people unable to
notice changes of 5 to 15 psi (20% to 50%) in passenger car operation.
See my post about not getting your "shorts in a bunch" about air pressure.
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