Tire pressure: door placard, sidewall max and TPMS light
Where the factory tire pressure placard is, why the sidewall number is a maximum, what turns the TPMS light on, and what to check after mounting.
The pressure that counts is on the door
The right tire pressure is the vehicle maker's recommended cold pressure, printed on the Tire and Loading Information placard, usually on the driver's door jamb. The number molded into the sidewall is a maximum, not a target.
NHTSA puts it in capital letters: the correct pressure is what the vehicle manufacturer has listed, NOT what is listed on the tire itself. Michelin says the same about the MAX PRESS marking. It tells you what the tire can withstand, not how the car should run. Filling to the sidewall number is the common mistake. The opposite one, a tire that has been slowly leaking for a month, is the one the TPMS light is there to catch, and only once it is well down.
Where the placard is, and what is on it
Federal standard 571.110 covers vehicles with a GVWR of 10,000 pounds or less. It requires the placard on the driver's side B-pillar. If there is no B-pillar and the driver's side has two doors opening in opposite directions, it goes on the forward edge of the rear side door. Failing that, the rear edge of the driver's door. Failing that, an inward-facing surface next to the driver's seat.
| Placard item (571.110 S4.3) | What it tells you |
|---|---|
| Heading | "Tire and Loading Information" on the placard, "Tire Information" on a separate pressure label |
| Vehicle capacity weight | "The combined weight of occupants and cargo should never exceed" a stated kilograms and pounds |
| Seating capacity | Total occupants, and how many front and rear |
| Cold tire pressure | Recommended for front, rear and spare, listed separately |
| Tire size | The size on the vehicle at first sale, and the spare's size |
| Optional extras | Load range, load index and speed rating to the right of the size |
| Footer | "See Owner's Manual for Additional Information" |
Two details trip people up. A full-size spare may just say "see above," and a car with no spare says "none." And the pressure may live on its own Tire Information label, permanently fixed next to the placard rather than on it.
Front and rear can differ. NHTSA's own five steps end with checking that all tires match, except where the front and rear are supposed to run different pressures. Read both lines before you reach for the air chuck.
Cold means three hours
NHTSA defines a cold tire as one that hasn't been driven for at least three hours, and tells owners to check every tire monthly, spare included. The placard number assumes cold. A car that just drove across town to your bay is warm, and its gauge reading is high.
NHTSA's guidance for that case is practical. If a warm tire reads below the placard number, add air up to the placard number. It may sit slightly under once it cools, and NHTSA says slightly under is safer than significantly under. Never let air out of a warm tire to reach the placard number. NHTSA's rule is to measure cold "or compensate for the extra pressure in warm tires," and bleeding a warm tire down to a cold number leaves it short once it cools. Recheck when you can get a cold reading. Tell the customer to look again tomorrow morning.
What turns the TPMS light on
Standard 571.138 applies to passenger cars, multipurpose passenger vehicles, trucks and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less, except those with dual wheels on an axle. All vehicles manufactured on or after September 1, 2007 have to comply, and NHTSA's consumer page puts it as every passenger car, light truck and van from model year 2008 on.
The trigger is in S4.2(a). The low-pressure light has to come on within 20 minutes once one or more tires is at or below the pressure 25 percent below the maker's recommended cold pressure, or the minimum in the standard's Table 1, whichever is higher.
| Tire type (571.138 Table 1) | Max or rated pressure (psi) | Minimum activation pressure (psi) |
|---|---|---|
| P-metric, standard load | 35, 44 or 51 | 20 |
| P-metric, extra load | 41 or 49 | 23 |
| Load range C | 51 | 29 |
| Load range D | 65 | 35 |
| Load range E | 80 | 35 |
A worked example. Standard 571.110 gives a sample truck label with P265/70R16 tires at 248 kPa (36 psi) cold. Twenty-five percent below that is 36 × 0.75 = 27 psi. Table 1's floor for a P-metric standard-load tire is 20 psi. The higher number wins, so that truck's light is required by 27 psi. Nine pounds low before the dash says a word.
That is why NHTSA calls the system a warning for a tire that is already significantly underinflated, and still tells owners to check monthly with a gauge. Direct systems read sensors inside the tires. Indirect systems infer pressure from wheel speed and other vehicle sensors. On a cold morning the light can come on and then go out as the tires warm up, which NHTSA traces to pressure sitting just under the threshold overnight. It is still a tire to check.
A steady light and a flashing light mean different things
Steady means low pressure. Flashing then steady means the system has a fault.
On a vehicle with one combined telltale, the standard calls for it to flash for at least 60 and no more than 90 seconds after key-on when there's a malfunction, then stay lit, and repeat every start until the fault is corrected. Other vehicles use a separate telltale showing the word "TPMS." Either way, a system in fault may not detect low pressure at all.
The owner's manual text that 571.138 requires names a cause you will see in a tire bay: malfunctions can come from installing replacement or alternate tires or wheels that prevent the TPMS from working. The same text tells drivers to always check the malfunction telltale after replacing one or more tires or wheels.
After mounting, before the keys go back
- Set each tire to the placard's cold pressure, front and rear from their own lines.
- Check the spare against its line on the placard, or the "see above" note.
- If the tires aren't the size on the placard, the placard pressure was not written for them. That includes an LT tire going on where the placard lists a P-metric tire with the same numbers: at the placard pressure it may not carry the same load. Michelin's FAQ says a replacement in a different size "should be inflated to provide the same load capability of the original tire size at the manufacturer's recommended pressure." The size conversion chart explains how a size change also changes the pressure question.
- Balance new tires. NHTSA says they should always be balanced when installed.
- Turn the key to on with the engine off. The low-pressure lamp should light briefly as a bulb check.
- If the owner's manual describes a reset or relearn step, do it the way the manual says.
- Watch the dash for a flash-then-steady pattern before the customer drives off.
Write the pressure you set on the receipt, next to the size. The receipt guide covers what else belongs there. On LT tires, also confirm the load range matches what the placard calls for; the LT load range chart and the load index chart cover the letters and the numbers. A pressure that is right for the wrong tire is still wrong.
Common questions
Where is the tire pressure placard on a car?
On most vehicles it is on the driver's side B-pillar, the door jamb post. Federal standard 571.110 allows the forward edge of the rear side door, the rear edge of the driver's door, or a surface next to the driver's seat, but only when the vehicle has no B-pillar or the placard can't go there.
Should I inflate to the max psi on the tire sidewall?
No. The sidewall MAX PRESS figure is the most the tire is built to hold, not the pressure the vehicle needs. NHTSA says the correct pressure is the one the vehicle manufacturer lists, not what is listed on the tire itself.
What pressure turns on the TPMS light?
Under 49 CFR 571.138 the light must come on within 20 minutes once a tire is 25 percent below the vehicle maker's recommended cold pressure, or at the minimum activation pressure in the standard's Table 1, whichever is higher. On P-metric tires with a 36 psi placard that is 27 psi; on load range D or E tires the Table 1 floor of 35 psi is higher.
Why does the TPMS light flash and then stay on?
That pattern means the system itself has a fault. On a combined telltale the standard calls for 60 to 90 seconds of flashing at key-on, then a steady light, repeated every start until the fault is fixed. Replacement tires or wheels that don't work with the TPMS can cause it.
Which vehicles are required to have TPMS?
Standard 571.138 covers passenger cars, multipurpose passenger vehicles, trucks and buses with a GVWR of 10,000 pounds or less, except vehicles with dual wheels on an axle. NHTSA says all passenger cars, light trucks and vans from model year 2008 on are required to have it.
When is a tire cold enough to check?
NHTSA defines cold as not driven for at least three hours. A tire that just rolled in reads higher than it will cold. If a warm tire reads below the placard number, add air up to the placard number. Never let air out of a warm tire to reach it. Recheck the pressure once the tire is cold.