That's real low for on-road driving IMHO, I don't care what tires you are driving on. Chances are you will experience a floaty ride with vague steering response, that will easily get unsettled in high speed turns. I barely approach those numbers off road, and that's for the gnarlier trails, let alone on pavement. Plus, you'd have to put up with the annoying TPMS warnings if you go that low.
I agree with the first part of their suggestion, though. I've always had luck with the LR recommended pressure front and rear (36/42 PSI for the LR4), and if it's good enough for a variety of OEM sizes and diameters, surely the ideal setting for a moderately oversized tire, whether A/T or not, can't be that far off that sweet spot.
Actually, the door factory psi numbers are not even close to the "ideal" pressure for larger tires, especially for any of you with heavier vehicles. In fact it becomes dangerous. No, not dangerous for all the time nothing is happening and your attention is 100%, but it is for when things "happen" and you need to do a critical avoidance maneuver.
Will a Land Rover flip over? Less likely than some vehicles but not impossible. The design is quite good for resisting roll over, even with my older Disco 1 compared to vehicles in same era. However, the lower the tire pressure, the closer the possibility.
Personally, I like those sorts of things to be as remote a possibility as possible.
The other benefits of proper inflation are realized in fuel economy and enjoyment of handling precision.
It used to be that if we put HD springs on a vehicle, the tires became the only way to not have such a harsh ride. With the air suspension now there's no excuse for low pressure any more.
The tires also last much longer with the "ideal" inflation. Too low will wear tires badly. This number will not be the same for my vehicle, yours, or the next person unless they all weigh the same and have the same size and tire type.
I only run E load range tires rated for 80psi. My LR is generally between 7000 - 8000 lbs so anything in the 40-44 range would be way too low for highway use. My pressure is set at 50-55 generally which works well.
Basically, correct PSI is determined by the weight on the axle. The door number assumes not only a very specific tire size and type but also a very specific weight range.
Tire shops will usually refer you to the door, regardless of any obvious reasons not to use those numbers, simply because of liability and/or ignorance.
