[Surly73]

Hi all:

Just a PSA on some things that folks may or may not know. In general I didn't pay much attention to the load rating on tires, as long as it was "enough". It may be valuable to know that the load rating alters the construction of the tires and affects how inflation pressure will change the load carrying ability AND THE CONTACT PATCH.

One of the tools at tiresize.com includes load rating tables and helps to translate inflation pressures between tire sizes and load ratings:

https://tiresize.com/pressure-calculator/

For instance 19" square 351Ms running 245/40/19, instead of the original 96Y or 98Y on the sport package cars my PS4S are technically XL (98). If I run the scenario through the calculator it changes the door sticker recommended pressures from F/R 35/39 to 36/37 to get the same contact patch and weight-bearing characteristics.

Interesting, right?

If you're running a size not on your door sticker, or you switch seasonally to different tires, you might want to play with this particular calculator to tune your ride and handling. (assuming you care at all what BMW recommended for the car).

Since I've just made significant suspension changes, I was going back to the basics while tuning handling and came across this scenario. My X-Drive only lists the 245/45/18 XL100 size on the door sticker and no others (since the X-Drive didn't have the wealth of options). It was interesting to use the calculator in combination with other references to translate.

[cdmulders]

Originally Posted by Surly73

Hi all:

Just a PSA on some things that folks may or may not know. In general I didn't pay much attention to the load rating on tires, as long as it was "enough". It may be valuable to know that the load rating alters the construction of the tires and affects how inflation pressure will change the load carrying ability AND THE CONTACT PATCH.

I did not know this, and much appreciate the info and the tool suggestion. I tried the tire pressure calculator, and by pure luck, my rear tires which I changed to a staggered setup some time ago just happen to be close to the right pressure.

[ezaircon4jc]

Originally Posted by cdmulders

I did not know this, and much appreciate the info and the tool suggestion. I tried the tire pressure calculator, and by pure luck, my rear tires which I changed to a staggered setup some time ago just happen to be close to the right pressure.

I tried it and saw only 2 load options, 96 and 98 for the front and 96 and 100 for the rears; the higher of the 2 being the stock numbers.

[Luky]

That's a good find. Thanks for sharing.