Tire pressure is the quickest and cheapest way to improve the performance of your vehicle in off-road conditions. 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. So, let’s get to this tire inflation guide for serious off-roading.
Tire Footprints Depends on Pressure
After dropping the air pressure from 30PSI to 15PSI the vehicle easily climbed where it could not before. It was a difference comparable to shifting from 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.
Primary Rules
- Increase pressure approximately 3psi for each 10mph over 20mph until normal highway pressures are reached. For instance: A 3000 lb. vehicle with 31×10.50R15 tires driving at 40mph is expected to have about 15psi in the tires (9 + 3 + 3 = 15).
- Decrease pressure by approximately ½ when in very soft snow. The only exception is a 33×9.50R15 or 33×10.5R15 tire because it generally benefits from an increase in pressure.
- Decrease pressure by approximately 1psi for every 2-inch tire diameter is increased beyond this chart, assuming the equal increase in the tire’s width.
| Tire Size/ GVW | 2000 | 3000 | 4000 | 5000 | 6000 | 7000 | 8000 |
|---|---|---|---|---|---|---|---|
| 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 |
| 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 |
| 29×8.50R15 | 10.5 | 12.5 | 14.5 | 15.5 | N/R | N/R | N/R |
| 30×9.50R15 | 8 | 10 | 12 | 14 | 16 | N/R | N/R |
| 31×10.50R15 | 8 | 9 | 10 | 12 | 14 | 16 | N/R |
| 32×11.50R15 | 7.5 | 8.5 | 8.5 | 11 | 13 | 15 | 18 |
| 33×9.50R15 | 9 | 10 | 12 | 14 | 16 | N/R | N/R |
| 33×10.50R15 | 7.5 | 8.5 | 8.5 | 11 | 13 | N/R | N/R |
| 33×12.50R15 | 7 | 8 | 9 | 10 | 12 | 14 | 16 |
| 35×12.50R15 | 6 | 7 | 8 | 9 | 10 | 12 | 14 |
| 36×14.50R15 | 5 | 6 | 7 | 8 | 9 | 10 | 12 |
| 38×15.50R15 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
*N/R = NOT RECOMMENDED
The pressures in this chart below are fit for most heavy-duty FWD: rock crawling, mud, sand, snow, etc., under 20mph. It should be added that these pressures are stated as a starting point only and, due to various other variables involved like rim width, tire construction, or weight distribution, every driver should experiment to find the ideal pressure.
16.5″ rims have no safety bead for the tire to be seated at the low pressures necessary for heavy-duty off-roading, so they are not mentioned in the chart and thus not recommended. However, they are fit for light-duty off-roading at pressures applied to the pavement.
WARNING! Be cautious when driving with partially deflated tires (any pressure other than the manufacturer’s recommended pressure) no matter on or off the pavement. If you drive too fast while turning with partially deflated tires, you can pull a tire’s seal off. So, you will lose all the air in that tire within seconds, and that will result in your vehicle rolling over or getting out of control, leading to death, severe injury, and/or property damage. The dangers of traveling with partially deflated tires are NOT LIMITED TO THE MENTIONED EXAMPLE!
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