How To Read Your Tires
The main reason that dual tire load limits are set at a lower rating than single tires is that tires paired up as duals do not always contact the road surface equally. Examples of this would be ruts in the road surface, climbing over curbs, mismatches in inflation pressure and/or remaining tread depth, to name a few.
This unequal road surface contact results in one of the dual tires ending up carrying more than its fair share of the load. In order to provide a “safety cushion” for when this happens, the maximum weight allowed is set lower than for a single application.
How to Look up Your Tire Pressure
- Most major tire manufacturers publish a “Load Ratings Schedule” on their website in pdf format.
- Find your tire size and the load rating (LR) as shown on your weigh report.
- Let’s suppose that the weights for your front axle are 5400 lbs. on one side and 5175 lbs. on the other. Each side of your rear axle weighs 9000 lbs. and 9200 lbs. Respectively.
- Use the heaviest end of your front axle of 5400 lbs. and follow the SINGLE load rating across to the first reading above your weight which is 5510 lbs. The corresponding required PSI is 95. In other words 95 psi will support up to 5510 lbs.
- Both front tires would use this pressure.
- For a dual application take the weight on the heaviest end of that axle of 9200 lbs. And look up the required pressure on the DUAL chart. You can see that 85 psi will support up to 9380 lbs.
- All four tires on this axle would use this pressure.
When to Check Tire Pressure
- Check your tire pressure in the morning or before you have driven a mile. The tires must be cold!
- At a minimum check your tires once a month.
- If you are on the road check your tires every morning before you leave.
- Never let air out of a hot tire.
- For every 10 degrees F (5.5 degrees C) rise or fall in outside air temperature, your inflation pressure will go up/down by 2%.
- Inflation pressure increases 0.48 psi for every 1,000 ft. (305 m) in elevation.
Neglect can make Matters Worse
- A perfectly good tire, properly mounted and correctly inflated can lose between 1 and 2 psi per month.
- In just 6 months’ inflation pressure could be down by as much as 12 psi.
- According to the National Highway Traffic Safety Administration underinflated tires are the leading cause of failure, which accounts for 660 fatalities and 3,300 injuries each year.