Pretty sure everyone does this.

 

My tires are 255/70R17 a little bigger than normal.
I never run the door jam pressures of 39psi front, 41psi rear. around town I run about 35psi front/back In sand I have gone as low as 15psi, off road hard pack I run ~27psi, and on the freeway at speed, I run 37psi.

 

Because "trucks" generally come with 8 and 10 ply E-rate tires. These suv's do not. Additionally, the trucks that permit lower tire pressures while not towing have their entire chassis designed around these proper low-load and high-load inflation regimens; the Touareg does not. In fact, I run higher tire pressures in my Touareg, what the Cayenne calls for. Finer handling that is more crisp, less rolling resistance, less slop when braking/accelerating etc. The tires also wear more evenly. Touareg used lower tire pressures to induce understeer when at the limit for the average skilled bloke that may end up driving these, whereas the Cayenne will tend to oversteer.

 

Because "trucks" generally come with 8 and 10 ply E-rate tires. These suv's do not.

I also think the factory pressures on the Touareg are way too low and wear the outsides of the tires too much, especially on the front. I use 10 ply E-rated tires and inflate them to way higher than the factory rated pressures- I use 46psi front / 54psi rear based on this reasoning.

IMO, most Touaregs were severely crippled in both towing and offroading ability by using oversized wheels, and flimsy passenger car-like tires. Even with proper heavy duty truck tires inflated to high pressure, dropping down from 19" to 17" wheels made my Touareg ride smoother.

High pressures also make the vehicle a lot more stable in extreme crosswinds. I encountered an incredible wind storm a few years back, that had nearly all the vehicles off the road, and lots of semis and travel trailers overturned all up and down the highway. My Touareg with 10 ply tires at high pressure was able to drive pretty much normal, even with a high windage roof tent on top, and was pretty much the only vehicle on the road able to do so.

 

I run 38/42 F/R as the sticker says for the 255/55/R18 size.

 

I run 40PSI cold all round even with just me in the car

But I also have ****ty Winrun tyres on ATM which have soft sidewalls

 

255/60 18s. Cooper HTS. 38/42 when towing. Probably could be a little higher but seems ok after many many klms. I drop back to placard settings for low load/around town.

I use this principle to get them 'right'.

The inflation pressure of a hot tyre is usually the inflation pressure of a hot tyre is usually about 4 PSI higher than when cold. If you check your tyre pressures when hot and it is more than 4 PSI higher, then the cold inflation pressure was too low. If the hot inflation pressure is less than 4 PSI difference than the cold pressure, then the cold pressure was too high.

Good way to figure out what's needed for your rig, as tyres vary by size and brand and tread pattern and...

 

Tire life may also be impacted by road construction materials. Here in New Zealand our roads are generally rubbish, but the only comparison I have is Australian roads - I've never driven in the US or Europe but don't the US use a lot more concrete? FWIW I run 38/38 on 255/55R18 Cooper ATTs.