[worldswinner]

Mine is 30 with unstaggered 20inch tire
Looks like lil lower than recommended
Should I follow this?

[Ravenous666]

Usually the recommendation is quite ok and it was always a good match.

[TurtleBoy]

You should match the door jamb label when filing the tires when cold (60F or so). After driving the pressures shown in iDrive are adjusted for the tire temperature so if you are filling them when warm use those values.

[Sportstick]

Keep in mind the door jamb label advises of the proper inflation at GVWR, which means the full passenger and cargo load for which the vehicle is certified. That weight is also on the label. For more typical daily driver usage, you may find reduced inflation from those values is more comfortable while providing the performance and safety you expect. I run 36 psi front and rear, as I am almost always alone, sometimes with my wife in a front seat position, and rarely any cargo of significant weight in the rear compartment. When you measure your inflation, the temperature, per se, is not the issue but the tires should be "cold" in the sense that they are not heated from usage, but are at the ambient temperature of your environment, such as first thing in the morning, unless you park in a climate controlled garage overnight that doesn't represent the outdoor conditions. Tire pressure will vary 1 psi for each 10 degree F change in the ambient temperature, so seasonal adjustments are also necessary in addition to routine maintenance.

[avi66]

Keep in mind that in some countries the tyre pressure label shows pressure for different vehicle loads, not just full weight.

[TurtleBoy]

The pressures are also engineered so the vehicle handles correctly and that is why you see a difference between the front and rear. If you change from recommended make sure you keep the same relative difference between the two and don't run the same pressure in both.

[Sportstick]

Originally Posted by TurtleBoy

The pressures are also engineered so the vehicle handles correctly and that is why you see a difference between the front and rear. If you change from recommended make sure you keep the same relative difference between the two and don't run the same pressure in both.

The differential at GVWR is related to tire safety under load to prevent tire overheating and possible blowout from sidewall flex. The rear pressure is higher under these conditions due to an otherwise fairly balanced vehicle weight distribution being altered with rear passengers and cargo disproportionally adding weight in the rear. It is not necessary to keep a pressure differential in an unladen vehicle for a daily driver. It won't do any harm either, but will provide a somewhat harsher/bumpier ride. If that does not bother OP, having the differential pressures will keep the vehicle ready for more passengers and cargo. Vehicle handling with 36/36, especially in Sport mode with the Dynamic Handling Package, is excellent.

[TurtleBoy]

Originally Posted by Sportstick

The differential at GVWR is related to tire safety under load to prevent tire overheating and possible blowout from sidewall flex. The rear pressure is higher under these conditions due to an otherwise fairly balanced vehicle weight distribution being altered with rear passengers and cargo disproportionally adding weight in the rear. It is not necessary to keep a pressure differential in an unladen vehicle for a daily driver. It won't do any harm either, but will provide a somewhat harsher/bumpier ride. If that does not bother OP, having the differential pressures will keep the vehicle ready for more passengers and cargo. Vehicle handling with 36/36, especially in Sport mode with the Dynamic Handling Package, is excellent.

No, the difference is for handling and inducing understeer.

[Sportstick]

Originally Posted by TurtleBoy

No, the difference is for handling and inducing understeer.

Yes, that may also be true in addition to the safety factor for carrying loads but experienced in more extreme driving that doesn't routinely happen on the streets for most drivers. However, the purpose of the door jamb label is a regulatory-driven source of information to inform drivers about maximum load and the associated tire pressure to carry that load safely to minimize the blowout risk from an overheated, flexed tire. NHTSA does not regulate the finer points of vehicle dynamics. But, those who track their vehicles certainly want to be diligent about tire pressure to optimize handling. However, from experiencing the 30i with DHP, 36/36 psi does provide excellent handling in Sport mode and the vehicle has taken some decreasing radius entrance ramps at very "spirited" speeds very neutrally. When in Comfort, the rear does not exhibit unneeded harshness. OP may decide how to apply all this information to their use case.

EDIT: I was interested to see how the online community discusses this and I found both the point you made as well as the load-carrying as the primary concerns on different websites. To varying degrees and depending on how the vehicle is driven, either or both may apply.

[Ravenous666]

Originally Posted by avi66

Keep in mind that in some countries the tyre pressure label shows pressure for different vehicle loads, not just full weight.

Not only the label, but also the tpms menu has a setting where you're able to set load conditions for tire pressure recomendation.

[TurtleBoy]

Originally Posted by Sportstick

EDIT: I was interested to see how the online community discusses this and I found both the point you made as well as the load-carrying as the primary concerns on different websites. To varying degrees and depending on how the vehicle is driven, either or both may apply.

I have been doing a little reading also while sitting here waiting for a car wash and am leaning towards my original understanding being incorrect, at least not the main reason, and max load weight being the main factor. I have not found anything definitive but it seems like the majority on forums believe it is due to handling however looking at some articles and requirements for the label as well as info from manufacturers where they provide multiple pressures it seems like it is weight.

Like you said, probably a combination of both.