True pressures

Usually vehicles have the tyre pressures clearly marked on a plate inside the drivers door, follow the manufacturers recommendation.
Also Jayco vans have a similar plate attached showing the recommended tyre pressures. On my Jayco that plate is inside the front boot.

Johno, you may start a long thread here as tyre pressures can be a bit like tyre brands themselves in regards to opinions. The tyre placard is good place to start from the vehicle manufacturer, but I usually run 40 psi on tar roads, 26-30 on dirt and 16-18 on sand. This is the start pressures for me then I adjust to the conditions to let them down or put more air in. You need to drop the pressures in your van as well as your car for offroad. Hope this helps.

Standard is known as "4psi rule".
Start with the recommended, as per plate.
Measure cold, then measure after 100km.
Should be 4psi increase.
If more, then is too low (flex causes more heat, more increase)
If less, then is too high (not enough flex).
Check front and rear, Prado will vary up to 20psi dependent on payload carried.
Regardless, drop to 20psi and drive slower on corrugations.....feels like a different vehicle.
Based on 30.000km on all road types last year. I was running 40psi front and 50psi rear for near max payload.

The best bet is to weigh your car separately and then together with the van hitched to get their true weights loaded up like your going away don't forget to add extra for water, fuel if the tanks are low, passengers and how the vehicles are loaded. Then you could ask a couple of different tyre outlets for their opinion on pressure because without knowing weights and tyre sizes it would be a pure guess.

Hi Johno,
On the bitumen I run on my Toyota 200 series fully loaded towing a Tvan 45 on the front and 55 on the rear. The Tvan will be at about 35. When on the dirt I will run 25 at the front and 30 on the rear, 20 on the Tvan. My speed is limited to 80 km/ h. The key is to check your tyre temperatures frequently. The difference in the ride you will get is quite dramatic. It is still rough but the suspension "bang" is gone. The other thing to consider is tyre choice. Not a particular brand but "type". With the LT (light truck) construction the tyre wall is considerably stronger and the flexing that occurs with all tyres is much less thus tyre heating is reduced and thus lower pressures are possible. With standard tyres the issue of sidewall damage and over heating is always an issue. You will find many people do not believe in reducing tyre pressure, however I consider that it is an essential aspect of off bitumen driving and also a mechanism of helping to preserve non bitumen roads and tracks.

I had TPMS in my 100 ser and used to pump them up so that I got a 6 lb increase from cold to hot Usually ran rears at 45lb hot and fronts about 38 Van about 45-50 but van was probably 50% heavier than yours.

Interestingly the sunnyside ones were always a couple of pound higher than the dark side.

For about $15 you can buy a digital thermometer on Fleabay. I use it at rest stops to check tyre and bearing temps.
Going over the Simpson in May at 13/16 psi cold and 13 in the trailer, temps stayed at about 50-60 degrees. Same at higher pressures on bitumen.
Keith

Johno, to work out the pressure you first have to weigh the combination with your wdh on if you use one. Get the individual weights for each axle and from this you can work out the tyre pressures for those axles.

The pressure will be a percentage of the maximum weight carrying capacity for the tyres. An example of this is, say the tyre has a maximum capacity of 1000kg at a 65 psi then if the weight on that individual tyre is 600kg then the pressure should be 39 psi. There should be tyre pressure calculators out there for this. Naturally there is a minimum pressure you shouldn't go below, except when off road at reduced speed.

We have one of the best temperature gauges on us all the time. The hand is a very good gauge to use and I have used this all my life. I run a hand over the tyres and bearing caps and you soon pickup any abnormal temps.

van tyre pressure calculator
You could try this link which gives you a way to calculate the pressures for your van tyres based on the tyre designation and the axle weight.

On a 2008 Prado 120 D4D and with the vehicle being near max weight on Toyo Off Country A/TIIs I use 35 psi (cold) around town. This gets up to close on 39-40 psi at running temperatures. On gravel using HL I run at 25 psi (cold) which climbs to about 28-30 at running temperatures. This will also be enough for some LL work as well but if consistent hard off-road LL work required I will drop pressures to 20 psi (hot) when required.

I keep the tyres on my camper at the same pressures as the Prado.