Tyre/tire pressures and dealer techs
 

Is this just a Vegas thing, or are all US dealer techs lacking in numeracy skills? My XJ came back with about 41 psi in the tyres and rode like a plank on concrete stairs. An earlier brain donor put 140 psi in the donut, I suspect because he mistook the bracket around the psi number for a 1. Even the loaner Discovery Sport and Evoque had 45 psi and the rears skated until I corrected the issue. WTH?

My Nissan SUV gets similar treatment, although I got them to admit it was a local palliative for the way that model wandered on the OEM tyres at the posted pressures. It only took a couple of heads on sticks outside the castle for them to 'fess up....;)

Guys, IT'S ON THE PLAQUE INSIDE THE DRIVER'S DOOR. HOW HARD CAN THIS BE?

The numbers inside the door of your car are for "maximum comfort", not necessarily what is best for the car or the tire itself. Plus, those numbers are really only good for the factory tires. Once you step to a different brand tire, the pressures that need to be in the tires may vary.

If you really want to know what pressures should be in your tires, you simply take some colored chalk and rub a good portion of your tires with the chalk. Do this on all 4 tires. You then lay some colored paper in front of the vehicle that will correspond to where the chalk would touch the ground. Drive over the paper and see if you have an exact impression of your tires on the paper. If you see where the tread is better "developed" on the outside edges, then you are running low on air and the tire should be inflated to a slightly higher pressure (few pounds is all it normally takes). If you see where the center is better "developed", then you need to let out a few pounds. That method gives you the maximum wear for the tires and ensures you have maximum grip for safety.

Forgive me for this, but I'd like to chime in here. The stickers have various of recommended pressures for different applications. Some are for comfort, some for full load, and others for fast driving (usually 100+ mph).
Going to different tires still requires following the vehicle manufacturer's recommendations since the tire manufacturer has no clue what vehicle or settings the tire is going to be used in.

Also, it seems to me that the OP referenced warm tire pressure vs cold ones. In my specific application, the pressure goes up by 4-5 PSI from when the tire is cold to when it's warm. Which, quite possibly, made his perception of overinflated tires even stronger.

And finally, I can totally relate to the OP's beef with the techs. While I had my Jag, every single tech was f#@ing with the tire pressure. They would put the pressure for 16 inch while it was running on the 18s. It happened at dealerships and regular tire shops. They would do it even after I specifically asked them NOT TO touch the tires at all. #facepalm

Haven't had this issue with the current and previous Merc tho.

To clear up any misunderstandings, the tire pressures in my OP were measured cold. They gave my one loaner Evoque with the rear tires 12 psi over the door jamb number. The rear contact patch looked similar to that for a girl in stilettos.

Yes, I know when you change brand you often have to adjust your pressures even if the tire specs read the same. But 9 psi??? Not buying it.

If you think tire techs screw up tire pressures, they're also clueless about the proper Jaguar lug nut torque! It's 92 ft.-lbs. And they usually use the wrong size socket to remove the lug nuts, which causes them to strip. No worry, because you won't find out that they're stripped until you have a flat and can't remove the wheel!

Worth reading: https://www.jaguarforums.com/forum/x...-bolts-145997/