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Cla 45 2022. I went to look up what the tire pressure should be and the chart goes by speed rating for the tire. The tire is rated for 186 mph and on the chart on the gas cap door; it only has two ratings one 155 and 168 mph I called the stealership and they said that chart is for driving in Germany So he just said put 38 in the front and 37 in the rear .I asked where did you get those numbers, he said they just go by the tire . I decided I heard enough BS and moved on . So what pressure do you guys use front and rear .
It's not per speed rating of the tire. That chart is showing you an air pressure for most use and then what you need to bump it up to if you are driving really high speed. But what your dealer is saying is... you're not going to be driving over 250km/h so you don't need to use the higher tire pressure levels.
this is a picture I made with paint, is the official used system to calculate pressure for a certain load.
Its what you have to highen up the reference-pressure for higher speed, before putting it in the official formula. Standard load 36 or 35 psi, XL / reinforced/extraload, 42 or 41 psi. , most ZR tires are XL//.
I got hold of this formula end 2007, and went running with it, now call myself " pigheaded Dutch selfdeclared tyrepressure-specialist "
I determined in time my own formula, and simpler system for speed.
That last is , for every 10kmph / 6 2mph different/ 1 loadindex step different, higher speed/ lower loadindex, lower speed/ higher loadindex.
referencespeed I keep for all speedcodes ( also W and Y ) at 160kmph /99mph.
for the reference -speed and-pressure, the maxload is calculated by the tiremaker, and is given on sidewall.
For your 155mph= 250 kmph so 250-160=9li steps lower then given on tire.
then you only have to determine the weight on axles, the most tricky part in it all.
carmakers use GAWR's for it, or determined axleloads for 3 persons and a little load.
For speed carmaker uses max technical carspeed, or sometimes also given for 160kmph/99mph.
But If you know , you never go, not even for a minute, above 80mph, you could use that speed for determining best pressure. More comfort , but also more fuelconsumption.
I determined that for 160kmph/99mph determined pressure, and 10% added to determined axleload, gives maximum reserve, with still acceptable comfort and gripp.
Then calculating lineair is not even that bad, gives slightly to high pressure.
For who it interests the oficially used formula in Europe for all kind of tires , and in US for P-tires since 2006.
A=( B/C)^1.25 x D
In wich.
A is needed pressure
B is real load on tire
C is maximum load of tire
D is reference-pressure of tire( is cold and not the maximum cold pressure as given on P-tires)
^ 1.25 is power, like power 2 is squaire, and power 0.5 is root, on sciencetific calculators is a button X^y for that.
I When I checked my tires they were all at 40psi . Why is it so hard for Mercedes to give us the right pressure for the tires on your car for ever day use .That is why I asked the CLA 45 owners what pressure they use. I guess I will go with the lower pressure 36 35 .
this is a picture I made with paint, is the official used system to calculate pressure for a certain load.
Its what you have to highen up the reference-pressure for higher speed, before putting it in the official formula. Standard load 36 or 35 psi, XL / reinforced/extraload, 42 or 41 psi. , most ZR tires are XL//.
I got hold of this formula end 2007, and went running with it, now call myself " pigheaded Dutch selfdeclared tyrepressure-specialist "
I determined in time my own formula, and simpler system for speed.
That last is , for every 10kmph / 6 2mph different/ 1 loadindex step different, higher speed/ lower loadindex, lower speed/ higher loadindex.
referencespeed I keep for all speedcodes ( also W and Y ) at 160kmph /99mph.
for the reference -speed and-pressure, the maxload is calculated by the tiremaker, and is given on sidewall.
For your 155mph= 250 kmph so 250-160=9li steps lower then given on tire.
then you only have to determine the weight on axles, the most tricky part in it all.
carmakers use GAWR's for it, or determined axleloads for 3 persons and a little load.
For speed carmaker uses max technical carspeed, or sometimes also given for 160kmph/99mph.
But If you know , you never go, not even for a minute, above 80mph, you could use that speed for determining best pressure. More comfort , but also more fuelconsumption.
I determined that for 160kmph/99mph determined pressure, and 10% added to determined axleload, gives maximum reserve, with still acceptable comfort and gripp.
Then calculating lineair is not even that bad, gives slightly to high pressure.
For who it interests the oficially used formula in Europe for all kind of tires , and in US for P-tires since 2006.
A=( B/C)^1.25 x D
In wich.
A is needed pressure
B is real load on tire
C is maximum load of tire
D is reference-pressure of tire( is cold and not the maximum cold pressure as given on P-tires)
^ 1.25 is power, like power 2 is squaire, and power 0.5 is root, on sciencetific calculators is a button X^y for that.
Thanks for that INFO. But I need a tire pressure chart for dummies. I should not have to find my slide rule to determine what pressure I need in my tires just to go to the store with two people lol
Its all a mater of responcibity, if carmaker gives that lower advice for normal day use, and only a few used that for heavy loaded and/ or high speed, only once , and tires overheat, and create little cracks, that dont disapear, and crack further in time, until mayby only after 3 years, that far that tire blows, or treath seperation, they sew the carmaker.
the couwardly high advice will never give overheating, only discomfort , and sooner punctures.
But if you give me 3 things of tires, I can make a pressure loadcapacity list for that tire per tire or per axle, whatever you like, and with reserve added, so you dont have to do that yourselfes.
then I make using 90% of the loadcapacyty belonging to the pressure.
These 3 things are, and can be read from sidewall
1. Maximum load or load index
2. Kind of tire to determine the reference-pressure
3. Speedcode( less important, have my own system
Oh, and give max speed you want the list for.
Then determining the wheelweights or axleweight stays your responcibility, and again, thats the most tricky part in it all.
I When I checked my tires they were all at 40psi . Why is it so hard for Mercedes to give us the right pressure for the tires on your car for ever day use .That is why I asked the CLA 45 owners what pressure they use. I guess I will go with the lower pressure 36 35 .
It's not that hard. lol Unless you have a specific use case... according to that chart you use 36 front... 35 rear.
I see some other posts here with Ph.D level engineering calculations being shown... don't worry about all that. Mercedes says 36 front and 35 rear.
To explain further... that chart is saying... if you are driving upto a maximum speed of 155 mph, have 19 inch wheels and are NOT carrying 5 people and a trunk full of heavy cargo... you use 36 front and 35 rear.
Thanks for responding to my email regarding case 02950991. This will allow my team to quickly pull up your case details if any further questions arise.
I was able to look up the 2022 Mercedes Benz CLA 45 AMG 4 Matic. Looks like the original equipment for that vehicle is size 255/35ZR19XL (96Y). If you are currently running that size your PSI should be 39 in the front and 38 in the rear.
It also has an alternate original equipment of size 245/40ZR18XL (97Y) if you are running this size your tire pressure should be at 38 in the front and 36 in the rear.
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Consumer Care Department
Certified Michelin Product Expert
Made it with selfmade spreadsheet.
But tell me more about Rube Goldberg.
Edit: googled Rube, and dont agree that I make a simple thing complicated.
Now pressure determination is a lot of gambling, wich can lead to tire failure, and acidents.
My simple list only needs acuate axleweigt and max speed determination.
Composed already a new list.
Axleload for max 99mph/ psi/axleload for max 155mph.
51 psi is max allowed cold pressure for most normal car tires, some XL max 60psi, I could not underline the maxload at 155mph.
And mind max speed is the max speed, you wont go over for even a minute.
Also for 155mph I used 90% of loadcapacity belonging to the pressure, wich might be exagerated for a normal car.
But for 99mph this 90% gives max reserve with still acceptable comfort and gripp, and so can also be used for 75mph for instance.
06-17-2022, 11:45 AM
