"I am a newbie. Just 5 weeks with my 2017 Newmar Bay Star 3113. I need some
help understanding just what would be the correct or appropriate tire
pressure on my coach. When loaded with my wife, dog and self, partial
food and clothing, tools, chairs, BBQ ladders, 2/3 water, full gas and
propane and misc stuff I got the following from the CAT scales: Front
axle - 7,300. Rear axle - 13,260.
Here is my dilemma: The dealer delivered the coach with about 85 lbs.
per wheel cold, but when I use the Michelin tire pressure chart for my 235/80R 22.5 XRE tires they should be just 75 lbs! I am
concerned that they will be "underinflated" and could build up excess
heat. Should I keep the 85 lbs. or lower the pressures?"
David, Welcome to RV fun.
For all things
tires (except buying) I obviously suggest you check my blog. I don't
expect folks to remember everything but if you spend a few minutes
checking it out you will learn how to use the "Label List" on the left
to find a post of the topic of interest. There is also a search box in
upper left. Now to your specific question.
1. We want to know
the heaviest load on your tires and since few RVs are perfectly balanced
side to side for weight we ideally want to know the "4 corner weight"
to learn the heavier end for each axle. Lacking knowing that number, IMO,
we can do a rough calculation by using 53% of the axle scale weight for
the RV when it was fully loaded (the expected heaviest it will ever be).
2. 53% of your front would be 3,870# and rear would be 7,030# or 3,515 on each dual.
Looking at the Michelin load tables we find for your size at 85 psi can
support 3,975 for single (front position) and 80 psi supports 7,050#
for two tires in dual position. Yes, we always round up.
4. Based on the above, your MINIMUM inflation would be 85/80. This is the number I would use for the low pressure warning numbers on your TPMS.
5. I recommend adding 10% and again, rounding up, that means 93/88 psi for your Cold Inflation Pressure or CIP.
In your case, given the close numbers for the front load, I would be
comfortable using 90 psi all around, as a single number is easier to
remember. This 10% gives you a nice cushion so you do not have to chase
your tire pressure around whenever the temperature rises or falls. You
could even get down to 85 psi before needing to "top off" the tire
6 All tires on an axle should be inflated to the same level for improved handling and response in an emergency situation.
7. I would set the TPMS High Pressure warning to 110 to 115 psi and your high temperature warning level to 160 F.
8 Remember CIP means when tires are at ambient temperature and have not
been in direct sunlight or driven on for at least two hours.
Finally, in your case, you are close to some numbers when we round so if your RV is more balanced than my suggested 47/53% you may be able to lower my suggested inflations by 5 psi, but only when you confirm your heavier end is less than 53% of the total.