I would be willing to bet that the 18" will be much softer than 20s and this is the kind of solution that OP is looking for.

I suspect upsizing to 255/60 R18 on 25 - 28psi will improve things.

True. He can opt for 255 60r18 and ride on less pressure, between 25 and 29psi as earlier noted.

Well, to be honest the 3rd row in the E70 and F15 is so terrible. It's fixed so low and has near inexistent leg and foot room. But it works well for my kids age 14 and below whenever there is a need to use it. So it's one of those things you hate and love at the same time.

3rd row is what it is and they actually did a fine job but the bigger trade off is no spare tire.

It's not for adults (although my wife has many adult friends who are plenty small enough to fit: Asian women often aren't very large). You need to move the middle seat forward to get any foot room of course

Oh, I wasn't disparaging the size or commodious-ness of the 3rd row. My wife is 5'0" and was mostly comfortable back there... until we started moving. Then she was less than enthused. :bustingup:

I wasn't suggesting 20s. That was a disclaimer based on the difference between what I have and that of OP. Whether it be 18s or 20s the goal should be a higher soft sidewall tire.

I would not drop air pressure lower than the minimum inflation specs. That said, you could try measuring air pressure when the tires are hot to see if lower inflation is still within proper range when tires have heated up from normal driving.

We were saying the same thing.

I was agreeing that he will have better luck with 18" than 20" and if you did better with 20" that bodes well for his case.


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Unless you are really pushing it you could probably easily use ± 8 psi with no significant problems besides tire wear and mpg.

I would use more psi in the back than the front to counter the heavier axle.


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Yes, MPG will decrease, wear will increase. Tire temp will also increase and handling will be compromised. When considering handling I think of the compromised capability to handle emergency situations and wet or slippery roads. X5 weighs over 5,000 pounds and has a high center of gravity. I expect that OP is looking for a longterm solution. Regardless, IMO, decreasing tire pressure should not be part of it.

I wouldn't change size of wheels either. I suggest doing some tire research and checking the validity of what you find with a couple of big volume tire sellers where there is lots of history as to what is the tire that provides the most comfortable ride. Here is one source for input: https://www.tiredeets.com/best-tires-for-bmw-x5/

I think the longterm solution will be a combination of tires that are well documented as a soft riding, comfort tire and changing shocks/struts.