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  #1  
Old 09-16-2021, 05:46 PM
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Identical Cars, Different Tire Pressure

When you own two identical cars you notice minor things...

One 2006 CDI, production date June 2005, has tire pressure recommendations of 28 PSI front, 30 PSI rear.

The other 2006 CDI, production date May 2006, has tire pressure recommendations of 28 PSI front, 33 PSI rear.

Not a big deal...but I guess the engineers revised their thinking over the course of a year.

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  #2  
Old 09-16-2021, 06:59 PM
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The engineers were asked to adjust the rear tire pressures to accommodate the weight of an un laden swallow in the boot. One of your sedans is specified for an African swallow and the other for the slightly heavier European swallow.

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  #3  
Old 09-16-2021, 08:37 PM
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I have always wondered why MB tended to specify lower pressure for the front tires. Most other makes that I deal with have it the other way around. Which would tend to make sense, since the front end tends to be heavier than the rear, at least on an average day.
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Old 09-17-2021, 02:02 AM
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Quote:
Originally Posted by shertex View Post
When you own two identical cars you notice minor things...

One 2006 CDI, production date June 2005, has tire pressure recommendations of 28 PSI front, 30 PSI rear.

The other 2006 CDI, production date May 2006, has tire pressure recommendations of 28 PSI front, 33 PSI rear.

Not a big deal...but I guess the engineers revised their thinking over the course of a year.
There are more important things in life than questioning about 3lbs of tire pressure. I would be more worry if it had been rocket pressure.
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  #5  
Old 09-17-2021, 11:45 PM
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Quote:
Originally Posted by tangofox007 View Post
I have always wondered why MB tended to specify lower pressure for the front tires. Most other makes that I deal with have it the other way around. Which would tend to make sense, since the front end tends to be heavier than the rear, at least on an average day.
I would guess that the higher pressure is meant to prolong the tread life on the rear tires. At the recommended pressure on my "97 E the rear tires wear on the inside at a ridiculous rate. I have had the alignment checked and new shocks installed, but the biggest help was raising the pressure to 30 PSI. I was told by a tech at an indi. that specializes in Mercedes, that you are lucky if you get more than 35K on a set of tires on a Mercedes because of the rear suspension. I went through a set in about that distance using the pressure on the gas door. I am hoping to do better now that I use 30 PSI all around. The rear wear is noticeably better.
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  #6  
Old 09-18-2021, 12:47 AM
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Quote:
Originally Posted by nelbur View Post
I would guess that the higher pressure is meant to prolong the tread life on the rear tires. At the recommended pressure on my "97 E the rear tires wear on the inside at a ridiculous rate. I have had the alignment checked and new shocks installed, but the biggest help was raising the pressure to 30 PSI. I was told by a tech at an indi. that specializes in Mercedes, that you are lucky if you get more than 35K on a set of tires on a Mercedes because of the rear suspension. I went through a set in about that distance using the pressure on the gas door. I am hoping to do better now that I use 30 PSI all around. The rear wear is noticeably better.
Interesting. Rear end sticks better, tires wear. I am OK . Rotate often is the key to tire longevity .
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  #7  
Old 09-18-2021, 02:20 AM
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Post Proper Tire Pressures

Almost all manufacturers advise softer than optimal tires pressures as this gives a slightly better ride .

Chalking or striping your tires will show you the specific best pressure for any particular vehicle regardless of tires, brands, driving habits, loading and so on .
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Old 09-19-2021, 09:03 AM
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To me it is simple. Rear with a load needs more tire pressure for load carrying capacity.
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Old 09-19-2021, 10:58 AM
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They may have come with tires of different load ratings. My Jeep asks for 35psi but switching to larger tires with a higher rating, we run around 42-44.
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  #10  
Old 09-19-2021, 01:20 PM
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Originally Posted by tbomachines View Post
My Jeep asks for 35psi but switching to larger tires with a higher rating, we run around 42-44.
And the logic behind that is....?

Where I went to school, larger tires require less pressure, not more.
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Old 09-19-2021, 01:36 PM
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Quote:
Originally Posted by t walgamuth View Post
To me it is simple. Rear with a load needs more tire pressure for load carrying capacity.
Spot on, on my cars the two pressures listed are called out as normal load, max payload, with the higher pressure at max. Given that cars are provided two weight specs, curb, and gross, the various tire pressures are related to accommodate those two weight differences
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  #12  
Old 09-19-2021, 02:41 PM
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Originally Posted by 87tdwagen View Post
Spot on, on my cars the two pressures listed are called out as normal load, max payload, with the higher pressure at max. Given that cars are provided two weight specs, curb, and gross, the various tire pressures are related to accommodate those two weight differences
If load was the determining factor, there is no reason for the front tire pressure in a passenger car to be lower than the rear in "normal" payload configurations.
As far a curb weight goes, when does a manned vehicle ever operate at that weight? (Okay, maybe it you have an near-empty fuel tank and a horse jockey for a driver.)

The majority of the passenger cars that I deal with specify higher pressure in the front tires, if there is a difference.
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  #13  
Old 09-19-2021, 04:03 PM
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Do you have front drive cars? My comments were mainly in reference to rwd cars.
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  #14  
Old 09-19-2021, 09:58 PM
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I agree with tangofox that larger tires should have lower pressure. Some folks see the max pressure value on the tire and mistakenly believe that that is a recommendation, rather than the do not exceed pressure. A few years back I had a new set of tires installed on a Bronco. When I drove home I was alarmed by how twitchy the truck was. I thought I had made a major mistake in the tires I had selected. I checked the tire pressure and found they all had 45 psi in them. I dropped them all to 30, and it drove like a new truck.
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  #15  
Old 09-19-2021, 11:18 PM
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Some time ago, I did some work on a Toyota van belonging to one of my neighbors. I noticed that all four tires were showing significant excessive wear in the center of the tread. Checked the tire pressure and found the tires to be severely overinflated. Brought the matter to the owner's attention; he explained that he was using the pressure listed on the sidewall, because his father had taught him to do it that way.

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