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Tire inflation guide for serious off-roading.

tire

Information source: www.oasisoffroad.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.

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 this chart below 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.  You will instantly lose all the air in that tire, which may result in your vehicle rolling over or going out of control, causing death, bodily injury and/or property damage.  The dangers of traveling with partially deflated tires are NOT LIMITED TO THIS EXAMPLE!

Please read "Terms of Site Use" also.

Information source:

http://www.oasisoffroad.com/index.html

www.oasisoffroad.com

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