Technical unclear on recommended tire pressure

[justintune]

Hello,

I have a 2021 fiat ducato 2.3L 160ps maxi, diesel. For tire pressure, in the manual it states: 4.3 front, 5.0 back but on the vehicle itself (on the driver's side door column) it states 5.0 for front and back. I guess I should trust what's on the door column right?

Thank you

 

[the green vanper]

I'd check what's marked on the tire

But I'd trust Knauf, they made the conversion, it is possible you've got different tyres than the standard commercial van.

 

[theoneandonly]

the most accurate way is to email the tyre manufacturer with the precise tyre and axle loadings (actual by wt if possible or VIN plate values).

 

[vexorg]

the most accurate way is to email the tyre manufacturer with the precise tyre and axle loadings (actual by wt if possible or VIN plate values).

I've tried that before, and they say it's up to the vehicle manufacturer to specify the pressure. Same tyre can be different pressures on different vehicles.

 

[theoneandonly]

I've tried that before, and they say it's up to the vehicle manufacturer to specify the pressure. Same tyre can be different pressures on different vehicles.

Thats intreaging Continental and Toyo were helpfull. Who shouldnt we bother.

 

[CheeseMonster]

I've tried that before, and they say it's up to the vehicle manufacturer to specify the pressure. Same tyre can be different pressures on different vehicles.

Michelin gave me front and rear pressures after sending them axle weights which I got at local weigh bridge. I run at our van at:
Front 4.48 bar
Rear 4.8 bar (this is lower than Michelin recommended and still harder than required in my opinion)

 

[vexorg]

I had dunlops, on one car they book said 37psi, on another car for identical tyre it was 32psi, similar weight on the cars. They said it was as much a function of the suspension as the tyre played a role in that.

 

[Reg 65]

Vehicle and tyre manufacturers tend to give maximum pressures because they don't know what weight you are carrying.
Michelin used to automatically recommend 80psi for all motorhome rear tyres, irrespective of weight, because they didn't trust you not to overload it.
So if you weigh the van you can do better than their recommendation with a pressure chart like this;

https://www.tyresafe.org/motorhome-tyre-safety/load-and-inflation-tables/

But - matter of opinion comes into this so thats why all charts don't agree.
For minimum rolling resistance and fuel economy you want the pressures as high as possible - but if you took that to its logical conclusion we would be driving on rock hard tyres that would shake us and our vehicles to bits. You have to have some cushioning for which you have to compromise fuel economy etc.
Where you draw the line is, to some extent, a matter of opinion.
So it doesn't do to try and get too precise about it - one recommendation will be slightly different to another. and neither is right or wrong.
Also bear in mind pressures are quoted cold and will vary with ambient temperature