Tire pressures and airing down for offroad

[HenryJ]

There are more benefits to airing down than the obvious increase in traction:

Increased Traction
A 25-30% decrease in tire pressure will yield up to 250% improvement in traction by increasing the depth and width of the tire on the surface.




Minimizing Environmental Disruption
An inflated tire will leave a noticeably more significant imprint on the terrain it is crossing which can be reduced by simply reducing the tire pressure. This works to protect and conserve our natural environment, meaning everyone can enjoy the off-road experience in the future.
Improved Ability to Travel on Soft Surfaces
The bigger the footprint, the softer the surface you can travel on as the weight of the vehicle is distributed over a larger surface area. When tires have very little or no traction they have a greater chance of getting bogged down or stuck in the surface or terrain that they are being driven through.
Reduced Resistance to Obstacles
Tests have shown a 40% improvement in overcoming obstacles at lower tire pressures due to the low pressure tires being able to contort over the obstacle. Therefore the drive becomes a less bumpy, much softer ride.




Improved Fuel Economy
Fuel usage increases when tires are at higher pressures because more revs and greater acceleration is required to take the vehicle over the off-road surfaces.
Safer at Higher Speeds
The increased surface area of the tires enables the vehicle to be stabilized at higher speeds on softer surfaces.

3 J's Striper Rigs

The benefit of decreased stress on the suspension components may be valuable as well.

[coffeedrnkr]

I don't even think it is a question if you should air down before offroading or not.

one thing I didn't see in the list is that there is less of a chance of a puncture or rip in your tire if you are aired down.

[gairbear]

SO exactly how much should you air down???

[coffeedrnkr]

I air down to about 12 psi with 33's on 10 inch wide wheels but I have to watch it b/c I have already put a big dent in the rim of my wheel.

if you are pretty much stock with stock tires and wheels personally I would do like 15-20psi

there isn't any exact pressure that you can do you just need to test different pressures and see what works best for the type of terrain that you will be on.

I am sure there is a chart somewhere for the different types of terrain and recommended psi

[quickbiker]

I've heard anything below 15 and you risk breaking a bead. Also if you want to go lower or a better chance at not breaking a bead, go with just a bit more narrow of a wheel than the tire recomends. I will be going with 35x12.5x15 and BFG recomends 8.5" wide wheel, but I am going with an 8" wheel. But the draw backs are it may wear a bit more in the center of the tire when aired up. Wider wheels let you run higher pressure on road for better mileage also. So, it's all a trade-off either way.

[killian96ss]

If you ever do break a bead I have seen a simple technique used before to get it reseated to put air back in. This technique only works if you have an available air source. All you need is a piece of rope and something to twist the rope with like a strong branch, crow bar, tire wrench, etc. You can also use a ratchet strap if you have one. Basically you wrap the rope around the outside diameter of the tire in the middle of the tread and begin twisting until it has compressed the tire enough to seat the bead, and then fill the tire with air. Be careful this can be dangerous if your not paying attention. If you have a ratchet strap they are much easier and safer to use. I'm sure this sounds wierd, but I have seen guys do this after popping off a tire @ low pressures. The other option which people are more familiar with is butane filling which works, but is also dangererous for obvious reasons.

Steve

[a2b]

SO exactly how much should you air down???

depends


i run 3 psi on my 38" sx's and i run 6 psi on my 37" mtr's


depends. on your tire size, compound, ply, wheel width, weight of vehicle, does the terrain really call for it, can you get by without it, etc....

[Walt]

I've only been really offroading once since I got my BFG AT's, and I was extremely impressed. The trail we went down (or up) consisted of mostly red clay and rocks ranging from pebbles to four or five feet in diameter (these were imbedded in the ground), so there was a variety of surfaces to cross. The worst parts were getting over the rocks. Most of them were at steeper sections of the trail, and it was raining a bit. I aired down to 25 psi (from 35), and slid all over the first section of rocks, which was one of the more difficult. After my second attempt, I aired down to 17 psi, and was simply amazed. I wish I had taken pictures. Those tires spread out like caterpillar tracks and would not let go I didn't have alot of trouble after that. Better tracking in the red clay too.

[HenryJ]

Found another good article: Bigredheep.com

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!

[quickbiker]

Just fill it till your knuckle bounces on it and ride it till it's bald!

[HenryJ]

Letting the Hot Air Out of Tire Talk Tire Pressures for 4-Wheeling