New tire air pressure; different recommendation

[B///MWGuy]

Hi, Ive bought two sets of tires from Tirerack and they listed the recommended tire pressure to be at 42 for XL vehicle (X5 with 255/50R19). These tires are different from OEM one, which was Bridgestone Dueller. New one is Pirelli Scorpion Verde all season runflat.

On my car's driver side door, there are two stickers regarding the tire pressure: yellow one with 100mph limit notation and a large sticker with more detailed spec.'

Yellow one states front to be at 32 psi and 38 psi on rear.
Larger sticker states 32 and 35 front and rear respectively.

Can I assume those specs are for my old tire only? Tirerack has responded to my email concerning this matter that they have tested the psi value on my vehicle and thus 42 (front/back)is the right one...

It does seem to drive better and I like it more on 42 than 32/35 psi. But from my recent visit to BmW dealership, they deflated it down to 32/35 for some reason.

Would it be okay to trust Tirerack's numbers? Im worried about overpressuring them when they get heated, as its max pressure is only 51 or 52 psi.

[mitch808]

The pressure you use is stated in your door jamb, there is no better authority. I dont care if you're named tirerack, michelin, or remotely look like the goodyear man or your middlenname is nitto. You always go with the door rating for 98% of situations

I personally use the rating assuming 5 adults, fully loaded for day to day. Thats often about 2-3psi higher. Resulting in a stiffer sidewall and slightly better mpg

If i were traveling at over 100mph for sustained periods, going a tad softer is warranted so as to minimize a blowout from over expanded tires due to heat.

[B///MWGuy]

Originally Posted by mitch808

The pressure you use is stated in your door jamb, there is no better authority. I dont care if you're named tirerack, michelin, or remotely look like the goodyear man or your middlenname is nitto. You always go with the door rating for 98% of situations

I personally use the rating assuming 5 adults, fully loaded for day to day. Thats often about 2-3psi higher. Resulting in a stiffer sidewall and slightly better mpg

If i were traveling at over 100mph for sustained periods, going a tad softer is warranted so as to minimize a blowout from over expanded tires due to heat.

Thank you for the answer. But may I ask why that is more reliable? I mean.. I'm pretty sure every tires are built differently and made of different material. How can a vehicle manufacturer set just one specification for all the different tires out there?

[mitch808]

A tire manufacturer doesn't know what car you're using, and a car manufacturer doesn't know what tire you're putting on.

What they do know are the vehicle weight, the load capabilities, and typical driving habits. Thus the door jamb sticker is based on that, and it doesn't matter if you're running 15" wheels or 24" wheels, you should follow that.

Different driving habits will then make an enthusiast want to tweak things like adding a few psi to reduce flex in the sidewall, or removing a few psi to say when in an AZ summer.

The PSI value on a tire is the MAXIMUM tire pressure when cold. It has nothing to do with the vehicle weight or load. Between an 1800lb 2 seat lotus and a 5000lb X5, assuming the same tire, should they both run 42psi? No.

Now, nothing wrong with adding a few psi here or there to get the handling characteristics you want. But do it based on YOUR testing, not some other testing done on a track in a different environment than yours.