Tire pressure?

[Tireman9]

Originally Posted by BFlinn181

Here we go again. Tireman9?

Ray is not wrong. Tire companies will say "run the tire placard inflation" as it is the RV companies responsibility to state the pressure necessary to support the GAWR. This is per federal regulation, so there is no way a tire company will contradict the RV company.


BUT IMO this is not the real question.

If you ask if it is acceptable from a tire durability standpoint, to run the inflation that is needed to carry the measured load as long as the speed is below the max rated speed on a tire. The answer will is Yes.

Both tire companies and RV companies know that a significant number of RV owners do not know the actual load on their tires. Also even if they do know the load and even if the do know there is a tire placard it is documented that many do not maintain the pressure needed to support the load.

The easiest statement they can make is "Run the inflation on the placard" as to say otherwise places them in legal jeopardy.

If you read my blog you will note I differentiate between Trailer and Motorhome recommendation. This is based on the specific Science of tire loading and durability. You will also note I tell people about minimums PLUS extra to give them reserve capacity.

IMO if someone is reading my blog and/or my posts they are demonstrating an interest in having a more fine tuned situation and hopefully having made the effort to be more educated will rise above the masses and pay attention to the steps needed.

Load & Inflation tables are published to establish minimum inflations needed for each specific size tire. So by definition it is acceptable from a tire durability standard to run those inflations.

Federal regulations do not ask what is acceptable or what the actual tire loading is. The Regulations just say the tire must have a placard inflation that results in a load capacity that is equal or greater than the GAWR.

[BFlinn181]

I wasn't really saying Ray, IN was wrong, just that I thought Tireman9 had explained on here and on his Blog that tires could safely be inflated for the actual load they carry, not a federally mandated sticker that shows tire pressures for the original tires at maximum axle capacity. Just seemed he was circling back around to post #3.

[jadatis]

Question to Tireman9.

How do tire- and car-makers react to if you keep your pressures higher then the advice of the car-maker, but lower or the same as the AT-pressure on tires-sidewall? Juridically I think they wont make a problem then.

I ask this because for the lighter motorhomes rear the adviced pressure for GAWR is often to low for the overloaded rear axle, wich could lead to tire-failure.

ofcource this does not go for if you want to use lower pressure ,because real weight on axles is substantially lower then the GAWR.

You also reacted on my post #19and #20 in your collective reaction.
The 99/81/86/76 psi and wondered why they where not rounded to 5 psi.
This is because I calculate in my spreadsheet, with an even saver formula then the official European one and sertainly saver then the official USA one for LT tires. But that is not the reason, I chose , when making the spreadsheet to round the end answer up to 1 psi/0.1 bar/10 kPa.
Can always chanche it to 5 psi , but why should I .

If you fill the tires with an analog device , you cant even read it that acurate and 99/81 will read 100/80 , so also OK .
And checked my post twice but oversaw the mistake about L speedrated.

On the lighter motorhomes used in Europe ( GVWR 3500kg/7700 lbs, because most people here have driverslicence B only for max 3500kg ) , Michelin and continental( Vanco) have CP tires.
those are mostly D-load/8PR tires with AT-pressure 4.75/4.8 bar/69/70 psi .
But they write maxcold pressure of 5.5 bar/80 psi on them.
Continental gives mostly both on sidewall AT69 psi( cold) and maximum cold pressure 80 psi. Michelin gave first max 80 psi only on those tires,but lager apart from the maximum load somewhere AT80 psi , so this states that the notations the tiremakers give are not always that consistent .

Most motorhome-makers stripe trough the advice pressures of car-maker ( often Fiat Ducato14) of about F4bar/59 psi/R4.5bar/65 psi and give new advice of 5.5 bar/80 psi all around.
That 5.5 bar Michelin wrote me to my question , it was for covering Peakloads, wich I translate as the often overloading.
So they dont support more then maximum load at higher pressure then AT, but in fact they advice that higher pressure to cover that higher load then maximum load, so a double moral.

Apart from that the motorhome-makers advice of 80 psi also for front is exagerated and people experiënce discomfort by bouncing, because driving in front seats so practically above the front axle,and also no optimal gripp for the most frontwheeldrive motorhome.
I calculated a few times for front a much lower pressure with a comfortable reserve even , sometimes even as low as 3.5bar/51 psi.
That would then give juridical problems because you go lower then the advice of vehicle maker,in this case the motorhome maker that gives higher advice then the vehicle maker ( Fiat) gives .
There is a Dutch saying wich translates as in this case , the motorhome maker heard the bell ringing but does not know where the clapper hangs(clapper translated with google).

[Tireman9]

Any and all pressure adjustments can only be made if you know the ACTUAL load on each tire position. The pressure MINIMUM would be the minimum pressure needed to support the measured load on the heavier end of an axle. This assumes you have no tire in an overload situation AND the total of both ends is not greater than the GAWR.
All tires on an axle should have the same CIP which means you set to the heavier end.