Tire Pressure
Tire pressure is another source of tire related arguments. Too little pressure and the tire pops off the bead, too much and it becomes easy cut the sidewall destroying the tire. Right in the middle the tire will stay on the wheel and conform to every pebble in the trail. Too much pressure and you may gain some ground clearance, i run my 36x12.5s on 15x10s at 25 psi on the street and 5-12 on the trail.
Tuning pressure for street use:
Tuning pressure for street use is not too difficult of a task. Learning to adjust your tire pressures for the different terrains you wheel on is a great tool to have. The correct pressure on the street is required as it ensures long tread life, decent ride quality, and predicable handling. Pressure at either extremes on the street will cause issues. Pressure too high and youll wear the center of the tread off the tires very quickly and this will also produce a jarring ride. Pressure too low and the tires will build up heat, this will kill the tire quickly and cause adverse and unpredicable handling. Many people look at the rated pressure on the side of the tire and assume tha is the running pressure, ITS NOT. The pressure listed on the sidewall is usually maximum pressure. Do not exceed the max pressure but that is also not where it needs to be for most short wheelbase Jeeps. The max pressure is directly connected to the maximum load if your tires are rated for 2,000 lbs each. So for an example you have a set of tires that read max pres 35 psi and max load 2000 lbs. If your Jeep weights 8000 lbs loaded you may well need to put 35 psi in the tires, but hopefully that does not appy to you (if it does you need to evaluate what you are bringing with you). Inside the door jam of most Jeeps you will find a label that has a recomended tire pressure, thats great with the stock wheels and tires but once they have been modified those numbers are useless. Here is a comon procedure for finding the correct street pressure for your tires.
Find and empty parking lot.
Inflate your tires to the max pressure listed on the sidewall.
Mark the tires accross the tread with a piece of chalk or crayon whatever really.
Drive straight forward several feet, be sure not to turn at all.
Look at the mark across the tread and see which part of mark has worn off.
If the mark has worn off at the center but not at the edges you have too much pressure (duh i already told you max pressure would be too much). Drop the pressure and repeat steps 2-5 until the desired pattern is achived. Be careful too low of a pressure will rub the mark so allways start with too much and work your way down. Loading will play a large roll in your quest for the perfect tire pressure. Normally the front will be slightly more loaded than the rear as a result of the positioning of the engine, likewise a fullled loaded Jeep ready for 2 weeks in the woods may balance that out and require more pressure in the rear then normal. Atmospheric pressure and temperature play roles too. Changes between the seasons can effect optimum tire pressure. A 10 degree drop in temp will drop your cold tire pressure by 1 psi. Most tires will lose about 1 psi per month due to porosity of the rubber compond in the tires and slight leaks at the bead. Also alititude makes a difference pressure will increase slightly with a gain of altitude due to the reduced atmospheric pressure. Final determination of proper tire pressure is seat of the pants, go test drive it and play around for a while.
** If this method will not achieve the correct pattern you have selected the incorrect tire width/ wheel width combination.**
Tuning Pressure for Trail:
Tuning pressure for trail use is a little more difficult of a task. Almost every experienced Jeeper knows to reduce tire pressure as soon as thy reach the trail. Airing down will create traction on many surfaces by increasing contact patch (the amount of the tires tread in contact with the ground) also by allowing the tire to conform to irregularities, usually the trail isnt perfectly flat. Also consider that while you air down you decrease the ground pressure (pounds force per square inch across the contact patch) and your ground clearance, so dont over do it. From my experience what i have seen on the trails is a pressure between 5-15 psi depending on the tire/wheel combination and the Jeeps weight. Tuning for the trail is more experience than anything else there are just too many variables at play to give a dinfinative number, have fun experimenting though!
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