How To Apply Tire Load Inflation Tables When Replacing Tires
When it comes to replacing tires, ensuring that the new tires are correctly inflated to handle the load they will carry is essential for safety, performance, and longevity. Tire load inflation tables are a critical resource for this, providing guidelines that help match tire inflation pressures with the load the tire will bear. Understanding how to apply these tables effectively is vital to maintain the correct tire pressure and to ensure optimal vehicle handling, fuel efficiency, and tire lifespan.
Understanding Tire Load Inflation Tables
Tire load inflation tables are charts provided by tire manufacturers and organizations like the Tire and Rim Association (TRA) or the European Tyre and Rim Technical Organisation (ETRTO). These tables specify the recommended tire pressures based on the load the tires will carry. The information is often broken down by tire size, with each size having its own table. The tables typically list the maximum load a tire can carry at various inflation pressures, providing a range of values rather than a single fixed number.
| Size Standard | Used by | Sample Tire Size |
|---|---|---|
| Metric | ETRTO | 215/60R15 |
| P-Metric | TRA | P205/50R16 |
| LT-Metric | TRA | LT265/70R17 |
| Flotation | TRA | 35x12.50R17 |
These tables are crucial because the load a tire can carry is directly related to its inflation pressure. An underinflated tire cannot support as much weight as a properly inflated one, which can lead to increased wear, reduced fuel efficiency, and even tire failure. Conversely, overinflating a tire can reduce its contact patch with the road, leading to decreased traction and uneven tire wear.
Tire size designation matters when it comes to application of tire load capacity and tire inflation. Tire size with same specifications but different tire standard designation may have different load capacity at any inflation pressure levels. For example, tire load capacity at same inflation pressure levels for 215/70R16, P215/70R16 and LT215/70R16 tire sizes are not the same. Just look their respective load capacity at 35 psi.
| Tire Size | Tire Size Type | Load Capacity @ 35 psi |
|---|---|---|
| 215/70R16/SL 99 | Metric | 1653 lbs |
| P215/70R16/SL 99 | P-Metric | 1709 lbs |
| LT215/70R16/C 100 (Single Tire) | LT-Metric | 1340 lbs |
Tire load index is associated with the maximum load a tire can carry under certain specified service conditions. But tire load index alone can not be used to determine load capacity equivalent of the replacement tire. In other words, different tire sizes with the same load index do not necessarily provide the same load capacity, and may also require substantially different inflation pressures. An equal or greater tire load index does not always correspond to equal or greater tire load capacity at all inflation pressures.
Note that metric and P-metric tires may not always be interchangeable. Replacement tire must have equal or greater load carrying capacity by inflation compared to the original equipment tire as specified on the vehicle’s tire information placard.
Some light truck tires may have two load indexes, for example LT215/70R16 100/97R. The first load index applies to single tire fitments and the second load index applies to dual tire fitments. When tires are fitted in dual assemblies (usually dual rear assembly), tire load capacity is 9% less than its single load capacity to account for the affect of road crown.
Tires with Reinforced (RF) and Extra Load (XL) built can carry additional load capacity at a higher inflation pressure compared to standard load tires.
According to the Federal Motor Vehicle Safety Standards, when a metric or P-metric tire is installed on a light truck, crossover, SUV, pickup or minivan the load capacity of the tire is reduced by about 10% of the original tire load capacity. For example, 295/40R19 tire has a maximum load capacity of 2,205 pounds. If you fit this tire on a light truck, then its actual allowable load capacity will be 1,985 pounds. So when replacing original equipment tires on your light truck or SUV with metric or P-metric tires, make sure the new tires have at least 10% more load capacity than the original tires. For example, if the light truck weighs 6,000 pounds, each tire should have load capacity of at least 1,500 pounds. If a metric or P-metric tires are fitted, each new tire should be able to carry at least 1,650 pounds.
How to read and apply tire load inflation tables
- Locate tire and loading information placard on the vehicle door jam, inside the glove box compartment, or inside of the trunk lid to confirm original equipment tire sizes and cold inflation pressures.
- Identify the tire size standard used (P-metric, LT-metric, Flotation or Metric) and refer to the appropriate tire load inflation table.
- Find the corresponding tire load capacity for the original equipment tire size at the recommended cold inflation pressure.
- Identify the tire size standard used for replacement tires and refer to the appropriate tire load inflation table.
- Find tire inflation pressure to which the corresponding tire load is equal to or greater than the original equipment tire.
- Inflate new tires to the appropriate inflation pressures.
Implementation Examples
P-Metric to Metric
Replace original equipment tires on Mitsubishi Lancer Evolution (P235/45ZR17 93W) with plus size 245/40ZR18 97Y RF tires. Recommended tire pressure is 32 psi for front tires and 29 psi for rear tires. Check P235/45ZR17 tire load inflation table to find load capacity at 32 psi (1354 lbs) and 29 psi (1272 lbs). Now check 245/40ZR18 97Y RF tire load inflation table to find tire inflation at load capacity of 1354 pounds or greater (1356 lbs @ 34 psi) and 1272 pounds or greater (1290 lbs @ 32 psi). Since you have to always maintain the original psi difference between front and rear tires, and the corresponding tire pressure for new rear tire is 32 psi, front tire pressure will be 35 psi instead of 34 psi. So proper tire pressure for new tire size of 245/40ZR18 97Y RF will be 35 psi for front tires and 32 psi for rear tires.
LT-Metric to LT-Metric
Replace original equipment tires on a Hummer H2 (LT315/70R17 121R) with LT325/70R17 122R tires. Both tire sizes are LT-metric so we use LT-Metric Tire Load Inflation Table to find the load carrying capacity at the recommended tire inflation of 37 psi, which in table falls between 35 psi and 40 psi. So to find load capacity at 37 psi, we do some simple math:
- First we find number of pounds per each 1 psi increase from 35 to 40 psi: (2685 - 2535) / (40 - 35) = 30
- Then we take load capacity at 35 psi (2535) and add 30 lbs x 2 psi = 60 lbs to get 2595 lbs
- Now we look for inflation value at 2595 lbs for LT325/70R17 122R tires. The closest is 2600 lbs at 35 psi. In this case we go by the rule that tire inflation in replacement tires must be same or higher than the recommended tire pressure for original equipment tires. So tire pressure for new LT325/70R17 tires should be 37 psi.
P-Metric to LT-Metric
Replace original equipment tires on a Ford F-150 XLT 4X4 Super Crew Cab (P255/70R17 110S) with LT265/70R17 121S tires. Using P255/70R17 110S tire load inflation table we find that at the recommended tire inflation of 35 psi it has load carrying capacity of 2337 lbs. As this is a P-Metric tire installed on a light truck, it has been de-rated by the vehicle manufacturer by a factor of 1.10, so the actual load carrying capacity is 2125 lbs.
Looking at LT265/70R17 121S tire load inflation table, we find that the closest load capacity that is equal to or greater than 2125 pounds is the 2255 lbs at 45 psi for a single tire assembly. So proper tire inflation for new LT265/70R17 121S tires is 45 psi for front and rear.
Importance of Regular Monitoring and Adjustment
Even after setting the correct tire pressure based on the load inflation table, regular monitoring is crucial. Tire pressure can fluctuate due to changes in temperature, altitude, and the load carried by the vehicle. Regular checks ensure that the tires remain within the optimal pressure range, preventing premature wear and enhancing safety.
It is also important to consider that tire pressure monitoring systems (TPMS), while useful, may not always provide precise readings, especially if the system is not calibrated for the specific load and tire size being used. Manual checks with a high-quality tire gauge are recommended for the most accurate results.
Applying tire load inflation tables when replacing tires is not just a routine task - it is a critical process that directly affects vehicle safety, performance, and tire durability. By carefully selecting the correct tire size, determining the appropriate load requirements, consulting the tire load inflation tables, and making necessary adjustments based on driving conditions, vehicle owners can ensure their tires are properly inflated and ready to handle the demands placed on them. Regular monitoring and adjustments are also key to maintaining the benefits of proper tire inflation, contributing to safer and more efficient driving experiences.
All listed guides, data and/or calculations are for informational purposes only. TirePressure.com does not warrant or make any representations regarding the accuracy of or the results of the use of this information.