BlackBeauty

Does anyone know what weight Porsche considers “partly loaded” for purposes of the reduced tire pressure guidiance? Fully loaded appears to be 1,400 lbs.

Also the manual is somewhat confusing as it lists “partly loaded” “comfort” and “standard” pressure recommendations that are the same, but comfort appears to be limited to a max speed of 168mph and standard has no limit.

Thanks in advance for the help- I know there are lots of threads on tire pressures but none seem to address the above.

jadatis

As " pigheaded Dutch selfdeclared tyrepressure-specialist" I can help you with this.
pressure advice is to give the tire a deflection that wont overheat any part of the tire, riding the speed the deflection is determined for.
higher speed》more cicles a second , so more heatproduction. This then has to be compensated bij lesser deflection, to give lesser heatproduction a cicle.
Its all about a temperature wich the rubber may not get above. This tmp is reached bij the balance between heating up and cooling down.
Cooling down is not speedrelated, but depends on temperature-differences between rubber and in and outside tire air.
If you understand this system, you can fill in yourselfes why the speed of 160km/h is used.
Your 168m/h is probably a miswriting, because maxload of tires is given for 160km/99m/h . For higher speed , a system is used for highening up the reference pressure. Can be that your tires are Y speedrated and for those the system gives 220km/137m/h for wich the reference pressure is used in the formula to calculate pressure for a sertain load on tire. 168 m/h is 270km/h and is speed for Y speedrated , above wich maximum load has to be lowered before putting in the formula.
So can be that they used that and you read it right.
You yourselfes know your used maximum speed wich you wont go over for even a minute.
If this is only 99m/160km/h, you can savely use the comfort setting.
But then be honnest , and it is the speed you sertainly wont go over for even a minute.
I dont agree with using the reference pressure in the formula for Y speedrated up to that 220km/137m/h , best is for Y also to use 99m/160km/h as maximum speed for that reference-pressure.
Reference pressure is the pressure for wich the maximum load of a tire is calculated for up to reference speed ( best keep it at 160km/99m for all speedcodes) and is not the maximum allowed cold pressure , they give on P-tires in Standard load and XL/reinforced/Extraload.
This reference pressure is for Standard load P tires always 35 psi/2,4 bar in USA system and 2,5 bar /36 psi in EUR system but then exeptions allowed.
For XL// referencepressure is USA 41 psi/2.8bar always and EUR 2.9bar/42 psi with exeptions.

I myself determined a better system for higher speed and rule of tumb in that is for every 10km/6,5m/h other speed , 1 Loadindexstep different, lower speed > higher loadindex, higher speed> lower Loadindex.
Only to calculate with.
This system use the tiremakers themselfes for LT tires and trucktires. Within a sertain range this rule of tumb goes.
This would mean for your 168m/270km/h you have to lower the Loadindex given on sidewall of your tires , with (270-160)/10= 11 steps , so for instance LI 97 becomes 86 before putting it in the formula .

In Europe before 2000 a normal advice was given for cars for axle loads determined by carmaker for 3 persons and a little load in car.
This gave for motor in front front higher advice pressure then back.
After 2000, to my opinion not coincidentially after the Ford/Firestone- affaire, Europe dont give this advice anymore, and normal advice is for 4 persons and load, and for that the GAWR's are filled in the formula, wich before 2000 was fully loaded advice.
Laws of nature though havent chanched , and you can still calculate the pressure for a sertain load and speed, and dont overheat the tires .

jadatis

And now about the load.
the 1400 lbs is probably the difference between empty weight and Gross Vehicle weight rating( GVWR) so maximum allowed total weight .
Can be that instead of empty weight its the driving ready weight , for wich they add a driver and some fuel to the empty weight.

So give empty weight and the way you load it normally ( persons and load) and try to determine weightdivision rear and front.
I can estimate it for you , if you give if motor in front or back( back probably for a Porche).
And then the hounestly given maximum speed you use and wont go over for even a minute.

Then from tires I need 3 things.
1 Maximum load or loadindex
2 Kind of tire to determine the reference pressure , so standard load or XL//.
3 speedcode of tires ( probably Y or even (Y) for over 300km/190m?/h )
Also give the sises so I can determine if I have to lower the maxload because of low Hight/Width division ( fi 255/30ZR19 97(Y)).
your avatar gives an older model so probably H/W div of 65 .
Sometimes for Porche special codes are put on tire.

If you then ride in other loads or speeds, for that ocasion you need other pressure.
For instance when you rob a bank of 10 gold bars and put them in the front( abouut 400kg/880 lbs, and want to run away from police at maximum speed, then you need a pressure sky high.

Penn4S

I think the OP will need therapy after that explanation.

BlackBeauty

Thanks guys. I'm just going to tough it out and go with the placard and when the P Zeros are done replace them with Michelin's.


The Avatar is actually Porsche's first LeMans car. I saw it at Pebble and met the owner (he's holding the key in the photo) and Rod Emery who restored it. Since then it's been at a ton of Porsche events including Amelia Island (I was lucky enough to be there).

LexVan

Try 36/40. Adjust 1 PSI, up or down, depending on how you drive.

Penn4S

Easy rule (JustMyOpinion) full load= frunk full, 2 passengers of size, and rear seats with stuff, follow placard. Comfort setting, normal driver and passenger, normal stuff to carry and speeds less than track speeds, I run 31 fronts on my 245x35x20 4S and 36 rear 305x30x20 and the car drives beautifully and handles like it is on rails. Did the same with the Pzero's.

4pipes

Jon D

I'm set up with +1 all the way around to account for passenger etc.

jadatis

Can also be that OP , when reading it 3 times, now understands what is important for the pressure, and he can now fill in himselfes why comfort parly loaded is lower then standard.
Because of the lower speed, but who drives faster then 168m/h .
lower pressure for the same weight means more deflection so more comfort and gripp.
But savety comes before everything.

chuck911

Yeah not only that but the tires actually have more total traction than at higher pressures. Oh the irony, of being instructed to inflate to the point you actually LOSE traction. This whole thread is one big non sequitur. In other words, just because everything above is true does not mean it has anything to do with what you should run.

worf928

chuck911

Right. And we can't even know how valid it is to use those carrying capacity numbers in the real world. That is because, at least so far as I know, those numbers are based on tests conducted by running the tires on a drum. So the tire flexes over an arc, not a flat surface like a road. The whole thing a stationary rig, not flying down the road with cooling wind rushing by the whole time. Then there is the test protocol, which involves so many minutes at speed x, followed by so many minutes at speed x+10, etc, which again bears no resemblance to anything anyone can do out there in the real world. I mean, nobody can drive 10 min at 180, let alone 10 min at 110, followed by 10 min at 120, followed by... so that by the time you even get to 180 you've already been doing over 100 for over an hour. Steady. Where on Earth anyone gonna do that? Yet we pore over these numbers and study them as if they have anything to do with anything we do.

BlackBeauty

Thanks everyone. According to the placard on the door, full load is 600lbs and recommended pressure is 35f and 45r. The manual says 34f and 44r for full load and 31f 39r for partial load, but all of those pressures are recommended for an ambient temp of 68 degrees. You lose 1lbs of air for roughly each 10 degrees you drop.

I asked the dealer and they fill comfort settings (I'm on the East Coast) to, ready for this...30f and 34r.

It's barely hovering around 45 degrees where I am. I think I'm going to go with 31/39 and see if that makes an appreciable difference.

I can't wait to burn through these P Zeros and get some Michelins...

worf928