Welcome to Gear Grinders 4 Wheel Drive Club!

Established in 1971 and located in Ridgecrest, California, we are a family oriented group of four-wheelers dedicated to promoting responsible off-road fun and protecting our natural resources.Our club takes pride in its support of Tread Lightly on Public lands. We are comprised of outgoing, fun loving, patriotic and responsible members who share the same love of off-roading and the outdoors. Guests are always welcome, so contact us if you will be in the area.  We’ll let you know where we are going and when.

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.


30 PSI 15 PSI 7 PSI

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.


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
31x10.500R15 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.


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.