Best pressure for BFG KM2 285/75/16 on KZJ70

[olival]

Hi !

I'm wearing 285/75/16 BFGoodrich KM2 on my KZJ70. The tires are mounted on 8X16 steel weels.

I'm very surprised by the hardness of the tires.
I mean for the off road, I have the impression that the tires needs to work at very low pressure.
I've tried first at 1.4 bar and it was like a tire at 2.0 bar. I'am obliged to decrease until 1.0 bar to have a better feeling in offroad and to remove the mud stack in the tire.

Do you have a feedback on the best pressure to use with this setup? I don't have bead-lock rims, so I am affraid to decrease more the pressure.

Picture at 1.2 bar:

Thank's for the advises...

Oliv

 

[Welby]

Hi - I run the same tires, 285/75 16s on factory alloys road pressure I run between 2.75 bar and 2.06 depending on the load at the time. For extended road travel I remain at 2.75 bar. for trail work with a reasonable load ( Recovery & weekend camping gear) I remain at 2.06 bar and can reduce to 1.3 bar. At that pressure the tires have a good bulge indicating a good footprint.

My truck is a 79 series V8, which I am guessing will be heavier that yours, especially with all the gear I carry. I would not go lower than 1.3 bar with my truck. The result of reducing pressure to low will result in rolling a tire of a rim, which is more than a little inconvenient. Depending on your the choice of terrain, if you are in a lot of soft stuff, ( MUD) the size tire you have on the truck should be fine, same as sand, but if you are on hills etc and steep stuff I would chose a narrower tire, as for the hilly terrain you need a certain amount of ground pressure to get grip. A wider tire on hills is less than Ideal I have found. But again it depends on the weight of you truck.

Hope that helps

http://forumcdn.ih8mud.com/images/attach/jpg.gif

 

[Capitalguy]

On my BJ70 I run them at 18psi off road, I have 33-10.5's with no bead locks.

 

[cicak]

looking at your tire there is enough tread on the ground 5 lugs worth. WE run 20PSI normally offroad with XT tires which is 4 lugs on the dirt with TRUCK tubes.

Your tires I assume at 14psi would run the risk of a tire roll off very quickly at under 20PSI if no bead lock or rim lock.

Personally I would not run under 1.5 BAR without a beadlock or tubes.

 

[olival]

I agree with all of you, with my previous tires (retread Black-Star Caïman 235/75/16, only the frenchies know is I gess) 1.4 bar was perfect.

But the BFG seems to be less "flexible" at the same pressure. The weight of the KZJ is around 1.7 to 1.8 tons. I think that the V8 70 series are much more heavy. It try it on the road at 2.2 bar, I was useless, the rig was following his own way. At 1.8, it's better, the car go where I ask for...

 

[Welby]

I agree with all of you, with my previous tires (retread Black-Star Caïman 235/75/16, only the frenchies know is I gess) 1.4 bar was perfect.

But the BFG seems to be less "flexible" at the same pressure. The weight of the KZJ is around 1.7 to 1.8 tons. I think that the V8 70 series are much more heavy. It try it on the road at 2.2 bar, I was useless, the rig was following his own way. At 1.8, it's better, the car go where I ask for...

I agree I would not run under 1.3 - 1.4 about 20 psi there is a real risk of rolling a tire off a rim, 20 psi if really needed, preferable at 25 psi (1.7bar) for my truck.

My 79 sits about 2.7 tonne with gear for a weekend, including recovery gear & camping gear.

 

[Radd Cruisers]

Tire pressure really depends on what you are doing and how fast you want to go and how much of a load you want to carry when you're off-road.

In my location, with similar sized tires, I would think nothing of going for pressures between 8 and 10 PSI (0.55 bar - 0.7 bar) and even lower in some situations. If you need to travel a little faster or carry more load, then something in the 18 - 22 PSI (1.2 to 1.5 bar) range.

If you have good quality tires, and good quality rims, then rolling the tire of the rim is not very likely - and not really that big a deal if you do (and are prepared for it).

To test how your tires respond to airing down, just pull the valve cores and watch for when the tire noticeably starts to develop a healthy bulge - which will probably start to happen at about 0.7 to 0.8 bar. Once that bulge starts, keep going and see how it develops, right until the tire is totally flat.

Then air the tires back up, looking for when that bulge starts to straighten up the sidewall and starts looking like the tire is at full operating pressure again.

There is no exact right pressure, there are many different ones that will work in different types of terrain and and with different loads and speeds. The main purpose of airing down is to increase footprint and traction, and if you have not gone down low enough in pressure to do that, then you need to keep going.

The other reason to lower tire pressures is to make the ride more comfortable over rough terrain. In that case, footprint and traction is not the key consideration, and it also requires experimentation to find what is right for you and your vehicle.

The most important thing you must keep in mind is that as you go lower in pressure, you need to reduce your speed and pay attention to how you are handling the vehicle - at 0.3 bar, for example, you need to keep speeds very slow and pay attention to how quickly you steer into corners and climb over obstacles, at 0.6 bar you can go a little faster etc...

A rule of thumb with local off-roaders (in situations that may be more commonly referred to as crawling), if you're not burping the bead every once in a while, you are probably running too much air pressure.


~John