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  #11  
Old 09-05-2019, 02:06 PM
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Quote:
Originally Posted by isarkisov View Post
Just checked my tires, looks like 40 PSI is the max pressure and there is "outside" marking.





Don't you think 40 PSI in front would be too much causing very harsh ride and hard on suspension?
Are these XL tires?
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  #12  
Old 09-05-2019, 03:12 PM
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Originally Posted by pshovest View Post
Not at all. It all depends on how badly you want to avoid buying new tires.
I'm surprised your max inflation pressure is only 40 psi. What type of tires are these? My Goodyear LS2 runflats need 50psi to get the advertised load rating. My non-runflats on other Bimmers are in the mid 40's. I run fronts at 40 and rears at 36 on the X5. Outside edge wear has all but disappeared.
I was wrong, when I looked at my tires this morning it says 50 psi max. Not sure where I got 40 psi

They are Pirelli SCORPION VERDE ALL SEASON RUN FLAT 255/50R19 107H XL. I just looked them up in Tirerack and here what it says:

"XL/RF tires required if 255/50-19 is used on rear axle. This requires higher tire pressure levels of 42psi for proper load."

I inflated to 40 psi all around this morning, should I go with 42 in the rear?
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  #13  
Old 09-05-2019, 03:13 PM
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Originally Posted by josiahg52 View Post
Are these XL tires?
Yes, 255/50R19 107H XL.
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  #14  
Old 09-06-2019, 01:30 AM
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Originally Posted by pshovest View Post
My Goodyear LS2 runflats need 50psi to get the advertised load rating. .



SO there is a maximum load that is specified by BMW... and to achieve THIS load, you should inflate the tires to the max pressure ON THE DOORJAMB PLACARD.

This can be independent from the maximum load for a given tire, and the inflation pressure to achieve that load.

My recollection is that you do not need to run tires at 50, 51, whatever to hit your maximum load rating that BMW states the car can handle. (and presumably BMW has determined 'at a fully laden configuration, the rear axle sees XXX lbs and therefore needs YY psi'.) And both of these numbers are UNDER the max tire load rating and max PSI ratings

So two different things... Correct?
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  #15  
Old 09-06-2019, 03:33 AM
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There is some pretty basic math to get even tire patches. I was curious so I did the math for my car.

My car typically weighs in as 1200# front corner and 1600# back corner (2400+3200=5600).

When loaded like I drive BMW recommends 32# front 39# back.

That works out to 1600/39=41 in.² patch rear and 1200/32=37.5 in.² front. Very close. To get them equal would take 1600/37.5=42.667 psi which I'm betting BMW did their homework and figure out it's best to let the back patch be bigger.

I get perfectly even tire wear and superb car-like handling. (cheat a little bit with $300 winter tires year 'round).


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  #16  
Old 09-06-2019, 12:25 PM
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I'm betting BMW did their homework and figure out it's best to let the back patch be bigger.

But WHY is this 'better' for BMW?

To give them a car that plows like a dog with horrible understeer so soccer dads cant get into trouble?

Or to set up the X5 as a world class driving machine??


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  #17  
Old 09-06-2019, 01:03 PM
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The second. my car drives like a car even when loaded with 1000# of tools.
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  #18  
Old 09-06-2019, 02:10 PM
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Originally Posted by ard View Post
SO there is a maximum load that is specified by BMW... and to achieve THIS load, you should inflate the tires to the max pressure ON THE DOORJAMB PLACARD.

This can be independent from the maximum load for a given tire, and the inflation pressure to achieve that load.

My recollection is that you do not need to run tires at 50, 51, whatever to hit your maximum load rating that BMW states the car can handle. (and presumably BMW has determined 'at a fully laden configuration, the rear axle sees XXX lbs and therefore needs YY psi'.) And both of these numbers are UNDER the max tire load rating and max PSI ratings

So two different things... Correct?
Yes, two different things.
I'd like to think that BMW did the calcs as you describe, but my gut tells me the lawyers were also involved to prevent oversteer. My point was that tire mfr's have a recommended pressure to achieve the tire's load rating and that BMW's pressures aren't even close to that limit. Virtually all of the 13 Bimmer's I've owned need 4-6 psi higher pressure than shown on the B pillar to get uniform front tire wear.
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  #19  
Old 09-06-2019, 02:15 PM
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Originally Posted by andrewwynn View Post
........When loaded like I drive BMW recommends 32# front 39# back......I get perfectly even tire wear and superb car-like handling. ........
You must drive like an old woman.......
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  #20  
Old 09-06-2019, 02:16 PM
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Originally Posted by ard View Post
But WHY is this 'better' for BMW?

To give them a car that plows like a dog with horrible understeer so soccer dads cant get into trouble?

Or to set up the X5 as a world class driving machine??


Woof, woof...........
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