Specifications

Tires
No brand or type tire recommendation is presented here. However, the first rule is that you do
not mix different types of tires on the vehicle such as radial, bias and bias-belted tires except in
emergencies. Good option is that all tires on an axle are the same brand, type of tread and same
age. A 'highway' version for the front and a 'traction' version for the back is OK. Current
recommendation is to replace any tire that is 5 to 6 years old. Unless you drive the motorhome
quite a bit, chances are they will have 70-80% of the tread still left on them after 5 or 6 years.
Check around – especially with your local tire dealers. You might find someone that puts on a
lot of miles on a light truck that will buy your old tires. They will use them up in a matter of
months, before they really get too old, and you can sometimes get up to half the price of the
new ones. Win-win for both of you.
The next rule is that the tire is of adequate capacity for the load it is required to carry and you
keep it inflated accordingly.
That previous front suspension example (4,300 lbs. front and 7,500 lbs. rear) for GAWR
indicated each front tire had to be able to carry 2,150 lbs. Each pair for the back have to be able
to carry 3750 lbs. or 1875 lbs. per tire. I added a sample chart from the P Chassis manual below
for this example. (Note the Load Range tire designation under each PSI reading.)
7.50-16 Bias Ply
PSI
30
C,D,
E
35
C,D,
E
40
C,D,
E
45
C,D,
E
50
D,E
55
D,E
60
D,E
65
E
70
E
75
E
Lbs per
tire-
Single
1620 1770 1930 2060 2190 2310 2440 2560 2670 2780
Lbs per
tire-
Duals
1430 1565 1690 1815 1930 2040 2140 2245 2345 2440
Looks like 50 PSI would be a good choice for both the front and rear tires in the chart above.
The placard for this particular motorhome said 60 PSI. This is probably because of the accepted
rule to add 5 – 10 PSI if you intend to hit 65mph or better and also to help cover a bit of loss
between air checks. A Load Range D or E tire will do the trick if you never cold inflate over 60
lbs. If you think you need 65 lbs., A Load Range E tire would be required.
http://users.sisna.com/cebula/P-Chassis-AlignmentProcess.pdf 12 Version 0.7 –Sep 14, 2005