Flame suite on - Correct Tire Pressure
 

So my wife drives a 5,000 lb SUV. It rides on 19" Continental Tires. The sidewall indicates max pressure @ 51 ps1. The sticker inside the driver's door shows fronts @ 32 and rears @ 38.

One tire must have a slow leak, as the Tire Pressure Monitoring system occasionally indicates low tire pressure. I think they are triggered at close to 30 psi. I have been running them at all @ 40 psi.

My question is - which do you follow? Our truck mechanic at work claims to have filled the tires to the max psi as shown on the tires - for his entire career. I called the local tire store and they said the same thing. I used to follow the door sticker, but it puts the fronts so close to the TPS threshold that my wife worries every time she sees the warning message. So the question of the day is, what psi recommendation do you follow?

IIRC the Ford Exploder/Firestone issue was exacerbated in part to people going by the tire v the door sticker.

Or at least that's what Ford claimed.

"Flame suite on"

WTF IS A FLAME SUITE? Is it some kind of contemporary musical composition, written by a gay composer?

Is it a flame that has more than one room? What the hell is it?

Oops, sorry. Got off the subject there, daepp. Learn how to spell, buddy, or else you'll get flamed.

Does the TPS on the vehicle directly measure tire pressure? The systems I know about actually measure wheel rolling radius using the wheel speed/revolutions output from the anti-locking brake system. If one of the wheels departs too much from the average, the system assumes tire pressure is low somewhere and triggers the warning light. When my daughter ruined a rear tire on her car and when we replaced it with a new tire (same exact tire) the difference in rolling radius between the new tire and the others with 10,000 miles on them would eventually trigger the low air pressure warning. There was never a tire pressure problem so after checking tire pressure she would just reset the system.

I would go by the OEM specifications (using an accurate gage); these were set to optimize ride, handling and fuel economy.

You should always go with the tire manufacturers recommended pressure.

I dont know what car this is but i know on our tacoma the sensors are triggerd by pressure because the spare will go low and set the light off. The sensor is built into the valve stem.

I always go by the vehicle manufacturer's recommended pressure.... for manufacturer's specified tires (NI,2, etc for Porsche). On other tires, assuming they are the correct sizes as specified by the vehicle manufacturer, set to the same pressures.
On non-stock sizes there will always be "discussions" over the correct pressure, depending on personal preferences and type of use.
The tire sidewall marking is not the specified pressure it should be set to.

Tire pressures should be checked with an accurate gauge when cold.

Take the SUV for a few hot laps around the block to get some heat in the tires. Measure the center, and the shoulders of the tires with a pyrometer. If the center reading is higher than the shoulders, then reduce the pressure, and vice versa.

;)

It's where Elton John and Liberace met to make music together and swap outfits. :)

I agree with Wayne. If the tires and wheels are stock, then the door jamb plate suggests the best pressure for the suspension that's on the car. If there are mods, then those numbers are obsolete.

As stated above, if they are stock sizes, go with the car specs, if they are not, go with the tire specs. However, keep in mind, the "max pressure of 51 psi", is just that, a max, that is not recommended inflation.

I think the problem is that the number on the sidewall is the MAX tire pressure, NOT the recommended pressure.

So, when you see (max pressure 51 psi) that doesn't mean fill it to there, it means don't fill it to 60 or 55.

tires work best in certain temperature ranges. Under inflation AND over inflation can over heat a tire.

i'm assuming they are not standard tyres so the sticker is now useless. Go with the maunfacturer's recommendation

My truck has a tire-monitoring system that directly measures the pressure of each tire. I can pull up what the pressure is on each individual tire in my dash display. The tires do not need to be rotating to take measurements. For example, if one side of the truck is sitting in the sun, I can see that that side will have higher tire pressures without moving.

Now I have my cold tire pressure at 35 psi--per the door sticker. I still have the OEM tires. When I am driving during the summer, the tires can hit 40 psi on the highway. Should I be concerned?

should be fine... the door label refers to cold pressures.

I guess I should clarify. Handling and braking are optimum at 35 psi. I noticed both suffer substantially at 40 psi. For example, I find it difficult (almost scary) to slow down and navigate most interstate off ramps when the tires have reached 40 psi. The exact same off ramps are no problem whatsoever when the tires are at 35 psi.

90% of the tire's rated max. pressure seems to work well, at least in my limited experience.

Q: So what happens when fed-mandated traction control starts being offered in all new cars?

A: Not only will it add gas-guzzling weight, but it will start throwing codes, or even dangerously affecting manual steering imput when different wheels or a spare is used.

Oh why, oh why can we not edit headings??? :)

The tires are optional oem on the car - an 07 GL450. The TPS is very sensitive, and keeping the tires at 32 in the front is very difficult without tripping the TPS.

Does anyone know if the door stickers are super conservative for some reason? There's quite a bit of discrepancy between 51 and 32. This is a heavy vehicle, the tire are enormous (275/55/19), and my entire family lives in this thing - I don;t think it should be so hard for the owner to determine the correct pressure. The dealer defaults to the door sticker, even though he admits the car comes with quite an array of oem tires.

The most important thing is the contact patch and the sidewall flex, both of which are spec'ed for the tire.

The car manufacturer, of course, doesn't want you to put on 70psi low-resistance tires on a stiff-suspension sports car. It would probably break an a-arm and they'd get sued.
There's a shock absorbtion balance between the tires and supension system, tire characteristics all over the map, and parts wear out, so it up to the consumer to tweak for best results.

You'll screw up the handling and braking if you don't keep a ratio between them.

Try adding 5 psi to fronts and rears. (37/43)

Do NOT put all tires at 51 psi.