How to Read Your Tire Sidewall to Set the Right TPMS Thresholds
Every number on your tire sidewall informs the alarm thresholds that determine whether your TPMS warns you in time — or too late. Here's how to read them correctly.
Most drivers who install a TPMS set alarm thresholds by guessing a number that seems reasonable — or by leaving the factory defaults in place. Factory defaults are calibrated for passenger car applications at passenger car pressures, and they are almost always wrong for RV owners and commercial truck operators running commercial tires at 70–120+ PSI. The correct alarm thresholds for your specific vehicle are derived from numbers that are already printed on the tire sidewall — they just require knowing which numbers to use, what they mean, and how to translate them into the low-pressure, high-pressure, and high-temperature values that tell your TPMS monitoring system when to alert and when to stay quiet.
This guide decodes every relevant marking on a commercial and RV tire sidewall and explains exactly how each one informs threshold configuration. By the end, you will have the specific inputs needed to configure your TPMS alarm values correctly for your actual tires and your actual load — rather than for a generic vehicle the manufacturer imagined when setting the defaults.
The Sidewall Decoder
What Every Number on Your Tire Actually Means
Reading a Commercial RV Tire Sidewall
MAX LOAD 2756 LBS @ 80 PSI MAX PRESSURE
DOT XXXXXXXX 2419
The Critical Distinction
Max Pressure Is Not the Recommended Operating Pressure
The most common threshold configuration error is using the MAX PRESSURE figure from the tire sidewall as the correct cold inflation target — and therefore centering alarm thresholds around that number. Max pressure is the maximum the tire casing can hold safely under static conditions. It is not the recommended inflation for the vehicle's actual load.
The correct cold inflation for a specific vehicle at a specific load is found in the vehicle's tire placard (door jamb sticker) or in the tire manufacturer's load-inflation table — not on the sidewall. The sidewall max pressure is the upper structural limit; the load-inflation table gives the pressure required to carry a specific load at a specific speed rating.
Load Index Reference
Translating Load Index to Maximum Load per Tire
| Load Index | Max Load (lbs) | Common Application |
|---|---|---|
| 108 | 2,205 lbs | Light commercial van — single rear |
| 112 | 2,469 lbs | Transit / ProMaster rear — light build-out |
| 116 | 2,756 lbs | Sprinter rear — standard commercial load |
| 120 | 3,086 lbs | Class C rear — heavier chassis applications |
| 122 | 3,307 lbs | Class A light motorhome — single rear axle |
| 126 | 3,748 lbs | Class A standard — dual rear consideration |
| 129 | 4,079 lbs | Heavy Class A — near commercial territory |
Setting Thresholds Correctly
The Three Alarm Values and How to Calculate Each One
Low Pressure Alarm
Set at 15–20% below the correct cold inflation for your actual loaded weight — not the max sidewall pressure. For a correct cold inflation of 75 PSI, set the low alarm at 60–64 PSI. This provides a warning window before the structural risk threshold while avoiding false alarms from normal morning temperature variation.
High Pressure Alarm
Set at 15% above the cold specification, or at the max sidewall pressure minus 5 PSI — whichever is lower. For a 75 PSI cold spec, set the high alarm at 86 PSI. For a tire with 80 PSI max pressure, set it at 75 PSI. This catches summer heat stack overinflation without alarming on normal friction heat buildup.
High Temperature Alarm
Set at 175–185°F. Most commercial tire manufacturers rate maximum continuous operating temperature at 200–220°F. Setting the alarm at 175–185°F provides a warning window before the structural limit — and on aging tires, the alarm will fire at this level before pressure deviation becomes measurable.
Dual Rear — Single vs Dual Load Rating
A tire marked 120/116 has a single-tire rating of 120 (3,086 lbs) and a dual-tire rating of 116 (2,756 lbs) when mounted with another tire on the same side. When calculating required inflation for dual rear positions, use the dual load index — not the single-tire number. This is commonly misapplied, resulting in underspecified cold inflation on dual rear positions.
The Grundig RV TPMS supports configurable alarm thresholds for all monitored positions. The Grundig S08 extends this to 218 PSI for heavy commercial applications where the load index and required inflation exceed standard RV TPMS ceiling limits.
Grundig RV TPMS
116 PSI ceiling. Configurable low, high, and temperature alarms per position. Set thresholds to your actual sidewall-derived values. $119.
$119
Shop Now →Solar TPMS 6-Wheel
Individual readings per position — inner and outer duals reported separately. Set dual-rated inflation thresholds correctly for each position. Solar powered.
$109
Shop Now →Grundig S08 TPMS
218 PSI ceiling for high-index commercial tires. Configurable thresholds for 8/12-wheel configurations where sidewall specs exceed standard RV limits. $259.
$259
Shop Now →Set the right thresholds. Get the right warnings. All systems support configurable alarms · Free shipping · From $119
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