365/80 R20 XZL Tire Pressure

[julius0377]

Looking for some information on what tire pressure to run on the new truck, this is the setup:

Michelin XZL 365/80 R20 all round in single fitment, about 4200 kg load on the rear axle and 3600 kg on the front.

The data I have:

Delivery pressure and recommended by dealer: 85 PSI all round.
Instruction manual states: 47 PSI for the rear, 37 PSI for the front.
Michelin website states 76 PSI for 6500 kg load, but nothing for lower loads.

I'm thinking of running a higher pressure than what the instruction manual states, as the tires seem to baloon/flex a lot over even small bumps on the low pressure, and the steering/handling gets much more heavy at higher speeds.

The delivery pressure is definitevely too high, the truck is bumpy on normal road surfaces and everything shakes and rattles about. I'm currently running 62 PSI at the front and 70 PSI at the rear, this is comfortable on roads and the carcass does not flex as much on potholes etc.

Let me know what you recommend and your experiences

 

[charlieaarons]

Tire load/pressures are pretty linear. If Michelin says 76psi for 6500 kg axle load then use 50 psi for 4200kg and 43psi for 3600kg. For offroad conditions try 75% (32/38) for under 50kph, 45% (20/23) for soft sand under 20kph, according to Mercedes' pressure advice for 365/80R20 XZL in the Unimog owners' manual. Be careful about debeading at 33% "emergency" pressures (15/17) for short distances under 10kph.
Be sure your weights are correct, be sure to weigh the truck fully loaded. You have a camper, make sure you have the water and fuel tanks are full and make a generous allowance for "stuff" like food, tools, spare parts. I'd guess another 500-1000 kg for "stuff" to be safe, about 80% in the rear. Make tire pressure adjustments accordingly.
I think 50/62 psi would be safe for any conceivable collection of stuff you choose to carry, ASSUMING your weights were with full tanks.

Charlie