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240 RECOVERY, CHAPTER 7 ______________ |
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Load your 4X like you typically use it. Make sure it's on the flat and level and ensure your tires are inflated to your normal street pressure. Measure the height of the wheel, straight up from the ground to the very bottom of the wheel (rim). Note the front and back may differ. Take 75% of this number. Now deflate the tire until the wheel is at this 75% height off the ground. Finally, re-measure the pressure. This is your soft-going optimum pressure. It will most likely be much lower than you're comfortable with.
Overall, I'm looking for smooth, easy, cool-engine sailing when I lower my tire pressure. I want to be able to take off easily after I stop. I do not want to struggle to move. With too much tire pressure, you may notice your engine heats up a bit. Higher engine temperature in the sand is a sure sign you need to reduce tire pressure still more. Has the "Big Numbers Myth" struck? Lower tire pressure gives you a bigger footprint. Mother Nature knows big feet work or why would She give camels and polar bears such giant bottom features? It also gives you the effect of slightly lower gearing due to a decrease in rolling radius. Lastly, it reduces what I've named obstacle-rolling resistance. This is the tire's ability to mold over rather than have to climb up a minor impediment.
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So
what does the ol' Coyote really do if the 75% number is so surprisingly
low? Mine is typically 6 or 7 PSI! I usually run 9 or 10 PSI when fat
feet are needed. I know for a fact that much above 12 PSI is virtually
useless for 15-inch wheels in soft sand, snow and mud.
The
Big Numbers game is what prompts us to buy a 200-PSI tire gauge or
portable compressor. Why do you need 200 PSI other than the fact that
the glitz guys have made you think it's better? I only carry 25 PSI in
my tires. A 200-PSI pencil gauge doesn't even start to register until
the pressure hits 20 or so. How are you going to measure 10 PSI if the
gauge doesn't start to move until twice that? I actually carry two
gauges. One is a 0-60 dial gauge and the pencil tops out at 20 PSI.
Reduced
tire pressure really works. Be prepared to air up or drive very slowly
to the first available air pump when you get back to the hard black
stuff. It's down right dangerous to do otherwise! Airing up and
compressor details are covered in Repairs of both Volume I and II.