Yes, they should or shouldn't be, for the reasons I stated, which I guess wasn't clear.

Stock is called stock for a reason. They are all the same, more or less, and all D1's weigh the same, within a few pounds, given the same specs.
There is a plethora of aftermarket tires of all sizes, load ranges, makes and styles. There's no way that Land Rover could provide data for every possible combination of tire and vehicle spec.

You have several options for determining correct accurate inflation pressure.

1. Keep your vehicle stock and use OEM tires and inflate per the manual.
2. Ask someone who is using the same part number tire on the same spec vehicle outfitted the same as yours.
3. Use the tread pattern chalk/paint test.
4. Use an IR thermometer to measure tread temperature.
5. Call the tire mfg and tell them the PN of the tire you're using, the axle weight of your Disco and ask them what their data shows for the correct pressure.

Anything else is guesswork.

 

I was looking for more scientific reasoning which the last 3 of your suggestions seem to be. Thanks.

 

When I had my 2001 Montero, it stated for speeds under 100mph and no load to run 26psi on all four tires.
For speeds over 100mph and no load to run 40psi.
Then it said if loaded and under 100mph to run 35psi.
If loaded and over 100mph to run 45psi.
I had never and have yet to see another car with tire psi recommendations for speeds in excess of 100mph.

Now back to your question, the harder (more psi) you run a tire the cooler it will run and the better your mpg will be because you will have less contact with the road.
If you over inflate your tires to much the center of the tread will contact the road and not the edges, add weight and the tire will flatten out and make full contact.
I run my work van at 75psi for the rears (80 is the max on the tires) and 65 on the fronts.
I think 35-40 psi is a good all around for the average person with a unladen Disco, assuming your tires can handle the 35-40 psi, the fewer the ply the lower the max psi.
Running to soft of a tire will reduce mpg and increase tire wear and increase your odds of a blow out (Ford vs Firestone, remember that? Ford said to run the tires at 26psi, they over heated, blew out at highway speeds and people died)
The softer the tire the smoother the ride, the harder the tire the rougher the ride.

 

my old(er) mercedes has this as well, as i believe the rolls does also... though not in the gas flap but rather in the owners manual in the case of the rolls.

i think its a fairly common thing for european cars

 

On the Montero it was on the drivers door jamb.
I had to re-read it several times to understand because I had never seen that before LOL!!!

 

I had read that the primary factors as far as the tires go are the load rating and the number of plys. I have had mine at 36 all around. I have not rotated the tires yet, but noticed the fronts are wearing the outside slighttly more. Rears still look excellent. Bridgestone (with the T blacked out to spell BRIDGES ONE, my last name) Duelers Load Range D.

Mine does have a two inch lift and is basically empty most of the time. I do carry heavy loads occasionally but it does fine.

I had a MB420SEL that also had elevated psi for cruising speeds over 100. Continental tires on it.

 

For clarification, you use it to measure several spots across the tread. If they are close then the inflation should be good.