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Weird difference in air pressure between 2006 and 2007 cars?

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Weird difference in air pressure between 2006 and 2007 cars?

 
Old 02-04-2019, 10:00 AM
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Weird difference in air pressure between 2006 and 2007 cars?

I have a 2006 E350 with sport package and just acquired a 2007 E350 with sport package and just noticed that the tire air pressure numbers are substantially different even though they're essentially the same car (3.5l, 7sp, 18"):

2006: 32 (35) front; 38 (42) rear
2007: 28 (29) front; 33 (35) rear

That's a 4psi difference in the front and a 5psi difference in the rear.

Any thoughts on why?
I'm running identical Michelin Pilot Sport AS 3+ on both and was wondering if I should err up or down or go exactly with the factory numbers?


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Old 02-04-2019, 10:46 AM
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Notice the sticker is for staggered tire size... are your tires from older car the same size front and rear?
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Old 02-04-2019, 10:52 AM
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They're both sport packages with 245/40/18 front and 265/35/18 rear.
The upper picture is the 2006 car fuel filler door placard, and the lower picture is the 2007 car fuel filler door placard with the substantially lower pressures.
I recall the 2007 models had something like 2,000 new parts, but that's a pretty dramatic drop in tire pressure.

Last edited by irondad; 02-04-2019 at 10:57 AM.
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Old 02-04-2019, 12:11 PM
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lower sticker does not list tire size.... so who knows.....as it is supposed to...

air pressure is calculated by axle load at the tire with normal driver and half tank of fuel.
tire on sidwall has load rating based on max pressure.

so you take actual load divide by tire load rating and mulitply by tire pressure at this max load. and round up up.

So maybe the staggered tires require bit more air then smaller ones for rear axle loads.

hence why you see an increase for more car loads.

also you see different for speed runs due to heat input to tires increase pressure which they are accounting for.
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Old 02-04-2019, 12:33 PM
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There might be cars weight difference, but tire pressure is a choice between comfort, tire wear and resistance (fuel consumption).
In times when mpg is top priority- manufacturers advise higher tire pressure.
I have a friend who drives his light Honda with 40 psi.
The 4-cylinder old car averages 35 mpg.
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Old 02-04-2019, 04:27 PM
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Same car, same size wheels, same size tires, same rated tires, same weight (based on my research)... yet 4-5psi difference between 2006 and 2007.
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Old 02-04-2019, 09:43 PM
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Originally Posted by irondad View Post
Same car, same size wheels, same size tires, same rated tires, same weight (based on my research)... yet 4-5psi difference between 2006 and 2007.
Look at your first picture.
The answer is there

That car came optioned from the factory with high load MO tires
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Old 02-08-2019, 09:29 PM
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2007 came with XL (extra load) tires as well.
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Old 02-10-2019, 11:05 PM
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My guess is that with the super low profile tires (which are almost always EXTRA LOAD), MB went with the high pressures in 2006 as did most manufacturers. I'm guessing that they saw higher center wear and did a rethink on how high they should be.

Backing off off on pressures would have improved tire wear and improved ride comfort. But I'll bet there was much discussion about this before it was changed this way.

Do you get high center wear on your tires? I'd bet you do at the rear but that's thrust related.

Just my two cents,
Peter
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