 |
|
Last Changed 5/18/2010
|
Tire Inflation
Proper tire inflation will mean you get the most from your tires in terms of ride, control, and wear. There is a maximum pressure
marked on the tire. This is the most pressure you can put in the tire while it is cold, meaning it has not been moving. As a
tire moves, the flexing of the tire body will generate heat and cause the tire pressure to rise. The maximum pressure rating has
taken this calculated into consideration.
Tire pressure should always be set when the tires are cold. You
should not adjust the tire pressure when they are hot. By
definition, "cold" means before the vehicle is moved, not a
temperature. If you check the tires when they are not cold, you
will actually be setting the pressure too low as a warm tire's air
pressure will be higher than when cold.
You do not have to fill your tires to maximum rated pressure. You need to fill them to a pressure
that at least has the value that provides the load capacity needed for the
load on the tire. This value is determined when you have your RV weighed. Once you
know the loading of your tires, then you can consult the inflation guide for your brand of tire.
Here is a sample inflation guide. You start with your tire size, for example LT235/85R16
E. This means you have a 16" rim, the tire tread width is 235
millimeters, and the height of the tread from the rim is 85% of the
235 mm, and the Load Range is E.
Then you follow the Single (S) or Dual (D) row. Tires in dual configurations have lower ratings to insure the tires do not rub on
each other.
For our LT235/85R16 example, we have a tire load of 2900 lbs. You look for the load value
that is just higher than the tire load you have.
In this example, you will find that a tire pressure of 75 psi will give you a tire capacity of 2905 lb. You will also see that you are in the Load Rate (E).
Load Range (E) tires have a maximum pressure of 80 psi and a tire capacity of 3042
lbs. for a LT235/85R16.
Note - you should always use the Inflation guide from the
manufacturer of your tire and for the model tire you have.
Note - we have seen Inflation Tables where axle loads (both wheels combined) were listed instead of individual wheel loads.
From our example you see that 75 psi will provide the tire capacity you need for your load and be under the maximum. The tire will
ride a little better than at Maximum Pressure of 80 psi.
Here are the effects of proper, over and under inflation.
|
|
|
Tire Profile |
|
 |
Proper tire inflation
With proper tire inflation, the air pressure causes the entire tread contact area to touch the road.
The air pressure matches the weight on the tire and the tire has flexibility without generating extra heat. |
 |
Over Inflation
When a tire is overinflated, the amount of air pressure
exceeds the amount necessary to hold the weight on the tire.
The extra air pressure causes the tread to bulge downward in
the center of the tread.
In this condition, the weight on the tire is being carried
by a small patch in the center of the tread. This
means there is less road traction from the tread.
Also, the extra pressure means the tire is not as flexible
as with proper inflation, resulting in a harder ride. |
 |
Under Inflation
Under inflation is the worst condition for a tire. There is not enough air pressure to hold the weight on the
tire. The result is the center of the tread buckles upward.
With the center of the tread not touching, or lightly touching the road, there is flexing in the tire sidewall because of the
tread not touching the road flat. This causes heat from the flexing which can lead to tire failure.
When the tread is not touching the road flat, the road traction is reduced. Also, in the underinflated state,
the tire will tend to squirm on the road, adding more heat. |
|
| |
