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Correct tire pressure?

 
Old 11-02-2014, 09:04 PM
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2013 ML350
Correct tire pressure?

Owners manual says 35 PSI all tires, Plaque on door says 41 PSI front 48 PSI on rear. Which one is correct. ML 350 2013
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Old 11-03-2014, 03:47 AM
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The high pressure advices on car are made so you can never sew the factory for to low pressure advice, Even if you are overloading within some limits with towbar load on. Something like "dont put an animal in the microwave oven".

The drive can be verry hard though using those pressures for normal use.
The 35 psi is more setup for your comfort but also already calculated for fully loaded and driving at top speed. So most likely can even use lower pressure savely.

I can calculate that save lowest pressure for your use if you give me some data of car and tires.
Do it with even saver formula then the European tyre-makers use and wich I once got hold of and went running with. Even call myself tire-pressure-specialist nowadays, thoug its yust a hobby and I am not working in the tire-business.

From car : Empty weight and the way you load it ( persons and load).
GAWR, GVWR ( Gross Axle/Vehicle Weight Rating)
Eventual camber angle ( if wheels are placed like this on the ( imaginary) axle /-\) , Maximum technical car speed or speed you wont go over for even a minute in your use.

From tires : Maximum load or Loadindex, Kind of tire to determine the needed pressure for the maximum load ( AT-pressure, reference-pressure, so P-tire or XL/reinforced/Extraload) and the speedcode ( Q to Y )
Nice would also be the exact sises and kind of tire like off road or winter-tire.
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Old 11-03-2014, 08:39 AM
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It is my wife's car and she uses it about 7000 mi per year for commuting around the Georgia mountains rural area small towns. We use it 1 or 2X's a year on freeways at max 80 MPH


GVWR on plaque is Front 1300#, rear 1600 #, total vehicle 2800#


Tires are Continental all season M+S 255/50R19 107H


Max pressure on sidewall is 60 PSI Max load on sidewall is 2149# (975 KG)


Usually 2 people in car ( 120# and 150# ), very light loads in rear when traveling on vacation. Usually nothing in rear when commuting.


Door plaque says 41 PSI front and 48 PSI rear Max load.


book says 35 PSI all tires.


We run Nitrogen in tires.


Is 35 PSI OK?
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Old 11-03-2014, 10:51 AM
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My rule of thumb is 35lb all around under normal loads and speeds with one/two people. Another rule of thumb is more load = more air. Towing and high speed driving also should have more air put in the tires than "normal". There are other "non-normal" driving conditions such as driving in sand, off road excursions, etc. but even in high pressure situations I still would never go over 40lb., at least not on American highways that have speed limits.

The confusion with our Mercedes ML is that it is a German car (even if put together in America). As such, the car manufacturer and tire manufacturer get together to cover most situations, hence, the different tire pressures shown on the car (one recommended psi on the door jam and another, much lower psi on the fuel door). Here is a quote to explain it: "The Autobahn's unlimited speed opportunities explain why many German vehicles identify alternate tire inflation pressures to accommodate higher than North American highway speeds and heavier than typical two-passenger loads. In order to accommodate higher speeds, the tire size and inflation pressure recommendations are tuned beyond what is branded on the tire's sidewalls. These increases in recommended tire pressure are usually determined by agreement between the vehicle and tire manufacturers". If the Autobahn had speed limits for its entire length, you probably would not have these multiple inflation pressure recommendations. If you want the whole story you can go to the link below:

http://www.tirerack.com/tires/tirete....jsp?techid=72
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Old 11-03-2014, 10:52 AM
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Googled your tires and found only XL tires in Loadindex 107.
this stands for 2149 lbs AT 42 psi in European system , American 41 so kept to 42 psi, Better to high then to low pressure .
But your 50% Hight/width division are given to high maximum load by the tire-makers so I concluded . Have to substract about 10% to give it a deflection that is save for them to laws of nature. For M&S tires wich have often large profile blocks that cover a part of sidewall so less flex of that allowed then calculated with by tire maker another 10% reduction.


So we go for calculating pressure advice from nex tire data.
Maximum load 1700 lbs AT 42 psi. H speedrated so max speed 210 km ,
Speed for wich the maximum load is calculated 160km/99m/h.
Because of your maximum speed of 80m/h ( pooh thats fast, is that allowed in America?) we dont have to add to that 42 psi for speed.
Also did not add for camber angle because you did not give and mostly below 2 degrees so not needed.

For the car we use for normal use 1300 lbs front and back so total weight of 2600 lbs , I dont think it will be more. But if you give empty weight and loaddivision ( so motor in front I presume) I can estimate it more secure.
A verry light vehicle I see , if thats right you have pretty oversised tires so a verry low pressure is expected.


Then calculated with the Original official formula used in Europe and since 2005 also in America, wich is adequate for P-tires and here XL/reinforced/Extraload, will come to next

1300/(2 x 1700)^1,25=13 psi !!!!!!!!!!!!!!
That low even , are all the data right.
In America they went before 2005 not lower then 26 psi but Europe that used the pretty right formula since about 1970 they dare to go as low as 21 psi.
So I calculate it without a power so linear , wich is sertainly not to low.
Then 17 psi rounded up , so use 18 and then with all the corrections and reserves it must be enaug.
Once calculated it for a Westfield , also a verry light vehicle with GAWR's of 880 lbs front and back and also came that low and prooved to be usual in that world .

What you might notice is that off-road this low pressure gives beter handling.
And on road its high enaug to give the tires a deflection that dont give damage to them.

If you gave though some information wrong,and real loads are higher ( mayby kilo's given ) then still the pressure stays below 35 even if lineair calculated
then ( 1300 X2.2) /(2 X 1700)* 42psi=33 psi all around.
For rear fully loaded then .
(1600 x 2.2)/3400 * 42=44 psi

So because I was myself surprised by the low answer I calculed even for if it where KG. So help me out of the dream and write if they are realy LBS given.
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Old 11-03-2014, 03:35 PM
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Why not go with the values posted on the fuel door sticker?
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Old 11-03-2014, 04:13 PM
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Originally Posted by DUTCH View Post
Why not go with the values posted on the fuel door sticker?


Fuel door says cold 32# normal load, 41# heavy load + 4# for warm tires ( I'm assuming that means all 4 tires), manual says 35 without specifying any range for heavy load. The drivers door jam sticker says 42 front and 48 rear fro cold settings. I have been going with 45 all 4 tires but why the wide discrepancy on the same rig is my concern. Dealer doesn't have a clue and is more confusing than helpful.


The warning code comes on if all tires are not equal, so what's a guy to do to follow the recommendations. Like I said this wife's car but I maintain it. I'm glad I drive Ford F-150 as I don't have all this conflicting info on it.
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Old 11-03-2014, 04:37 PM
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I use the values on the fuel door sticker on all of my cars, and they've never let me down.
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Old 02-10-2015, 09:29 PM
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14 ML 350 Blue Tec, 11 E 350 Coupe
I had a 2012 ML 350 BlueTec & asked the same tire pressure question. To many different answers, so I purchased a $2 tire tread gauge, set my front at 42psi & read at 44psi. Dealers told me adverage mileage was 22-26,000 miles. I traded mine at 42,000 with 6mm still left. I now have a 2014 & set same pressure. I rotate every 5,000 miles & use tread gauge to check for even wear. Good luck.
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Old 02-11-2015, 02:46 PM
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