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Information source:
www.oasis-off-road.com on-board air systems and tire deflators.
Tire pressure is the quickest and
cheapest way to improve the performance of your vehicle off road.
Lowering the tire pressure greatly increases the amount of tread in
contact with the ground. I have seen situations when a vehicle having
full street pressure was unable to climb due to wheel spin or lack of
traction. After dropping the air pressure from 30PSI to 15PSI the
vehicle easily climbed were it could not before. It was a difference
comparable to shifting form 2WD to 4WD. Reduced pressure allows the tire
to conform to irregular surfaces such as rocks. It also spreads the
vehicle weight over a larger area, allowing the tire to float more
easily over loose or soft surfaces.
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30PSI |
15PSI |
7PSI |
|
Contact area:
20.5sq.in. |
Contact
area:30.5sq.in. |
Contact area:
43.3sq.in. |
General Rules:
1) Increase pressure approximately 3psi for each 10mph over 20mph, until
normal highway pressures are reached. For example: A 3000 lb. vehicle
with 31x10.50R15 tires traveling at 40mph should have about 15psi in the
tires (9 + 3 + 3 = 15).
2) Decrease pressure by approximately ½ for extremely soft snow. The
exception to this is a 33x9.50R15 or 33x10.5R15 tire, which usually
benefits from an increase in pressure.
3) Decrease pressure approximately 1psi for every two inches tire
diameter is increased beyond this chart, assuming a corresponding
increase in width of the tire.
N/R = NOT RECOMMENDED
|
Tire Size/ GVW |
2000 |
3000 |
4000 |
5000 |
6000 |
7000 |
8000 |
|
215/75R15 |
11 |
13 |
15 |
N/R |
N/R |
N/R |
N/R |
|
235/75R15 |
10 |
12 |
14 |
16 |
N/R |
N/R |
N/R |
|
29x8.50R15 |
10.5 |
12.5 |
14.5 |
15.5 |
N/R |
N/R |
N/R |
|
30x9.50R15 |
8 |
10 |
12 |
14 |
16 |
N/R |
N/R |
|
31x10.50R15 |
8 |
9 |
10 |
12 |
14 |
16 |
N/R |
|
32x11.50R15 |
7.5 |
8.5 |
8.5 |
11 |
13 |
15 |
18 |
|
33x9.50R15 |
9 |
10 |
12 |
14 |
16 |
N/R |
N/R |
|
33x10.50R15 |
7.5 |
8.5 |
8.5 |
11 |
13 |
N/R |
N/R |
|
33x12.50R15 |
7 |
8 |
9 |
10 |
12 |
14 |
16 |
|
35x12.50R15 |
6 |
7 |
8 |
9 |
10 |
12 |
14 |
|
36x14.50R15 |
5 |
6 |
7 |
8 |
9 |
10 |
12 |
|
38x15.50R15 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
225/75R16 |
11 |
13 |
15 |
N/R |
N/R |
N/R |
N/R |
|
245/75R16 |
10 |
12 |
14 |
16 |
N/R |
N/R |
N/R |
|
265/75R16 |
8 |
10 |
12 |
14 |
16 |
N/R |
N/R |
|
285/75R16 |
8 |
9 |
10 |
12 |
14 |
16 |
N/R |
The pressures in the chart above
are suitable for most heavy duty four wheeling: rock crawling, mud,
sand, some snow, etc., at speeds under 20mph. It should be noted
that these pressures are suggested as a starting point only and,
because of the many other variables involved like rim width, tire
construction and weight distribution, one should experiment to find
his/her ideal pressure.
Since 16.5" rims have no safety bead to keep the tire seated at the low
pressures required for heavy duty four wheeling, they are not included
in this chart and are not recommended. They are however suitable for
light duty four wheeling at pressures ordinarily used on pavement.
WARNING!!!
Use extreme caution
when driving with partially deflated tires (any pressure other than the
manufacturer's recommended pressure) whether on or off pavement. If you
are traveling too fast while turning with partially deflated tires you
may pull a tire's seal off of it's wheel turning. Traveling at
speeds above 20mph for an extended period will overheat tire side walls
causing tire damage or side wall blow out.
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