Can't believe Sams Club did me this.

[Dftodd]

I was thinking I heard around a 10% below registered normal. My 2011 Ram 1500 will set them off around 36-37# when 40 is the registered normal. I have had several cases where I they would be normal but would have a big temp drop over a couple of days Like 60 to like 27 over a period of a few days. Jump in the truck and start moving and set off 2 or 3 before getting out of the driveway.

May be the difference between dodge and GM.

I know when I've switched to the screen in my wife's car, the other tires were 2 to 3 pounds of each other. Tire pressure is set to 30 psi on her car last time I checked and topped them at the house.

My trucks been 4 pounds low on one of them and it hadn't tripped. Truck tires are set at 36 psi.

 

[tomplum]

That Firestone recall came out at the right time for me. Tires were OK, but got into something out on some forest service roads and had 2 go flat. 1 dead. I was able to make it urban enough with a little compressor I had. Dealer said go get new ones, 4 or 5 I don't remember now. Brought him the old tires and the bill.

Last summer had a dead TMPS sensor , thought I'd grab a sensor put it in and get a set when the new tires go on. Well that sensor died, they gave me a new one. Still works, but if I get on the highway right after leaving home - it triggers the light and loses connectivity. Exactly at the same exit every time. Weird.

 

[RustyA]

Typical threshold is 10% or so. 4500 chassis RV is exempt due to gvwr. Shouldn't be though, some rvers are a little distracted, many install their own tpms including the towed vehicle they pull. Class A motorhomes don't even have a spare and lug nuts are 450 ft/lbs torque.

 

[Grumpycat]

I was thinking I heard around a 10% below registered normal.

NHTSA/DOT spec is an unbelievable 75% of nominal tire pressure. So if spec is 40 PSI then the warning light illuminates at 30 PSI.

 

[Grumpycat]

Last summer had a dead TMPS sensor , thought I'd grab a sensor put it in and get a set when the new tires go on. Well that sensor died, they gave me a new one. Still works, but if I get on the highway right after leaving home - it triggers the light and loses connectivity. Exactly at the same exit every time. Weird.

That intersection doesn't fail the TPMS sensor, the vehicle ECU fails to see it a period of time or given distance then it fails. Is not an "Missed the previous 30 second update!" So that intersection is the same time/distance from home or work.

You somehow know it is the new sensor failing? You have individual tire PSI display? And you know it indicates the correct corners of the vehicle, not goofed by a tire rotation?

When one sensor in a batch fails the others are not far behind. They rarely fail hard, usually takes 6 months from the first intermittent to final hard failure. Fails hard faster when it is cold. If goofy in spring they might go to winter before failing hard.

 

[Grumpycat]

The last time I was in Sam's was the tire department. Waited in line 35 minutes to talk to the one person at the counter. Watched the shop floor for lack of anything else to do. 5 employees walking around aimlessly doing nothing the whole time. No air wrenches hammering, nothing. 3 cars on lifts. During the 35 minutes one guy walked out and balanced a tire, rolled another tire back to the car. Then disappeared. Another guy kept coming out of a back room, to filing cabinet, put a sheet or two of paper in, took a sheet or two of paper out, and returned every 10 minutes or so to do the same thing.

When I finally got to the front of the line was told, "Sorry, we are all booked up. Come tomorrow." How about an appointment? "We don't do that." I heard my explicative echo from the far corners of the store. My membership was due for renewal in 2 days. Didn't.

Conversely Discount Tire is a top notch class act. Equal or better prices than Sam's. Or Costco.

 

[RustyA]

Again cold affects weak sensor batteries. Sometimes a reprogram will buy you some time, if one sensor is slow to or won't program that's your troublemaker.

 

[RandyT]

NHTSA/DOT spec is an unbelievable 75% of nominal tire pressure. So if spec is 40 PSI then the warning light illuminates at 30 PSI.

My nominal is 40 psi but normally set off the warning around 36-37 psi. But normally run then close to 50 due to the 10 ply rated tires that have a max inflation of 80 psi and the manufacturer recommends minimum pressure at 60# of max.

 

[Grumpycat]

NHTSA/DOT spec is an unbelievable 75% of nominal tire pressure. So if spec is 40 PSI then the warning light illuminates at 30 PSI.

Replying to myself:

49 CFR § 571.138 - Standard No. 138; Tire pressure monitoring systems. says about a screen down from the top (bold and italics added):

S4.2 TPMS detection requirements. The tire pressure monitoring system must:

(a) Illuminate a low tire pressure warning telltale not more than 20 minutes after the inflation pressure in one or more of the vehicle's tires, up to a total of four tires, is equal to or less than either the pressure 25 percent below the vehicle manufacturer's recommended cold inflation pressure, or the pressure specified in the 3rd column of Table 1 of this standard for the corresponding type of tire, whichever is higher;

Reading like a DoD engineer the above says an indication must occur when the above conditions are met, but doesn't say the indication can not occur earlier.

On Mercedes-Benz and Toyota TPMS systems from 2009 and 2007 with very very badly named "RESET" buttons the indicator signaled at 75% of the pressure present the previous time the RESET button was depressed.

See how badly the button is named? TPMS light? Push the reset button and your problem goes away! Only what you really did is memorize the current pressures as "correct" so the next time the light illuminates you will have 75% of the previously low 75%.

The neat thing about the RESET button is how a smart driver can manipulate the warning pressure. Nominal 36 PSI and you think 32 is a reasonable warning? Put 32/0.75 = 42.6 PSI in the tires, drive around the block, then RESET, and let the pressure back down to 36. Heck of a lot easier than fooling with Forscan or other tuners.

 

[two_bit_score]

I've been using Discount Tire since the late 80's.

We have never had a problem with Discount Tire. And, they have locations all over Texas. I had a tire losing air out in Midland once and pulled into a DS store. They plugged it and I was back on the road in no time. Always great service.