[FC] Rampside tire pressures

[James Davis]

      Load depends on the air volume a particular tire can 
hold.  Remember it is the volume of air in the tire that holds the 
vehicle up not the tire itself.  "P" series passenger tires are 
usually carry their rated load at 36 psi.  What you need to do is to 
calculate the air pressure needed for your vehicle load.
       I will assume Rampsides are loaded at 50% front and rear and 
side to side.  For a Rampside that list at 2,800 lbs wet and add 200 
for driver and 200 for passenger in the front, we come up with 1800 
on the front and 1400 on the rear; so, I will use 900 on the front 
and 700 on the rear in the example.  The tire example is a P195/75-14 
which is rated at 1400 lbs at 36 psi.  In the front tires, we need a 
minimum of 900/1400 of the rated air pressure or 23.14 psi.  Always 
round up so that is 24 for the front.  In the rear, the air pressure 
would be 700/1400 of 36 psi or 18 psi.  These air pressures will give 
the best ride, tire wear, and are consistent with tire manufacture's 
recommendations for radial tires. Since the Rampside rear tires are 
mounted on a swing axle suspension, I think it would prudent to add 
air to a 24 psi.  This will effect handling by increasing the spring 
rate of the tires and resulting in a choppier ride but more straight 
line stability.  The lower air pressure in the rear tires will allow 
more sidewall compliance giving better traction in marginal conditions.
      My Rampside weighs 880 LF,  760 RF,  700 LR, and 720 RR.  That 
is with only me aboard.  (The truck has a gasoline heater, anti-roll 
bars, and is air conditioned.)  With LT225/70-15 tires rated at 1764 
lbs at 44 psi, I run 26 psi front and 24 psi in the rear.  I pump up 
the tires to 32 psi all around when I load the truck heavily.
Jim Davis



At 07:48 PM 3/4/2006, you wrote:
>Ken,  since we're talking about ride quaity here, what air pressure 
>should I be running in the fron tire of my 61 Rampside?  I don't 
>load it down or anything like that.  Usually just me in the cab 
>(sometimes the wife too). I am running radials naturally.
>V/R  Paul C.