What a Load Range Chart Tells You
A load range chart matches the letter rating on your trailer tire to the maximum weight that tire can safely carry at a given air pressure. The letter (A through F, most commonly) is printed on the tire's sidewall. The chart shows you three things: the load range letter, the ply rating it represents, and the maximum load capacity at the recommended pressure for that tire size.
You need this chart because a tire marked "Load Range D" can carry a different weight than one marked "Load Range E," even if both are the same physical size. The chart prevents you from overloading a tire, which causes blowouts, uneven wear, and loss of control. Trailer tires fail suddenly and without warning when overloaded, so this is not a guideline—it is a hard limit.
The chart is specific to your tire size and brand. A 14-inch Load Range D tire has a different capacity than a 15-inch Load Range D tire. You will find the chart on the tire manufacturer's website, on the tire's packaging, or printed on a placard inside the tire shop. You can also request it from the tire retailer when you buy.
Key Takeaways
- Load range letters (A through F) indicate how many plies the tire sidewall can withstand and how much weight the tire can carry at its rated pressure.
- The chart shows maximum load capacity in pounds for each load range at the tire's recommended air pressure, which varies by tire size.
- You must know your trailer's actual loaded weight and the number of tires carrying that weight to find the minimum load range you need.
- Load range is not the same as tire size; two tires of the same size can have different load ranges and different weight capacities.
- Exceeding the load range capacity causes tire failure and is the leading cause of trailer accidents on the road.
How to Find Your Tire's Load Range Letter
The load range letter appears on the sidewall of every trailer tire, printed in large letters after the tire size. For example, a tire marked "ST225/75R15 D" has a load range of D. The letters run from A (lowest capacity) through F (highest capacity), though most trailer tires fall in the C, D, or E range.
If you cannot read the sidewall clearly, look at the tire's documentation or the receipt from when it was installed. If the tire is already on your trailer, you can also call the tire shop where it was purchased and give them the tire size; they can tell you the load range without you having to remove the tire.
Do not assume all tires on your trailer have the same load range. Trailers are sometimes repaired with whatever tire is in stock, so you may have a mix. Check every tire on your trailer separately. Write down the size and load range for each one, then use the lowest load range to determine your trailer's safe weight limit.
Reading the Chart: Size, Load Range, and Capacity
A load range chart is organized by tire size in the left column. Find your tire size first—for example, 225/75R15. Then scan across to the row for your load range letter. The number in that cell is the maximum load capacity in pounds at the tire's recommended air pressure.
Here is what a simplified section looks like:
| Tire Size | Load Range C (6 Ply) | Load Range D (8 Ply) | Load Range E (10 Ply) |
|---|---|---|---|
| ST225/75R15 | 2,150 lbs | 2,540 lbs | 2,830 lbs |
| ST235/80R16 | 2,270 lbs | 2,670 lbs | 2,980 lbs |
The "ply" number (6, 8, 10) in the header refers to the number of cord layers in the tire's sidewall. More plies mean a stiffer sidewall that can handle more weight and pressure. You do not need to remember the ply number; the load range letter is what matters. The chart shows it only for reference.
The capacity listed is per tire. If your trailer has four tires, multiply the single-tire capacity by four to find the total weight your trailer can safely carry. A trailer with four ST225/75R15 Load Range D tires can carry 2,540 × 4 = 10,160 pounds total.
Matching Your Trailer Weight to the Right Load Range
To know which load range you need, start with your trailer's actual weight when fully loaded. This includes the trailer frame itself, any cargo, water, fuel, or passengers. Weigh the loaded trailer at a truck stop scale if you are unsure. Do not estimate.
Divide the total weight by the number of tires on your trailer. For a single-axle trailer with two tires, divide by two. For a tandem-axle trailer with four tires, divide by four. This gives you the average weight per tire. Then find a load range on the chart where the capacity per tire exceeds this number by at least 10 percent.
Example: A loaded trailer weighs 8,000 pounds and has four tires. 8,000 ÷ 4 = 2,000 pounds per tire. You need a tire with a capacity of at least 2,200 pounds (2,000 plus 10 percent). If your tire size is ST225/75R15, the chart shows Load Range D carries 2,540 pounds, which is enough. Load Range C carries 2,150 pounds, which is also enough but leaves less margin for error.
The 10 percent margin matters because weight is not always evenly distributed. Cargo shifts, and one tire may carry slightly more than the average. A margin protects against this and against the slow pressure loss that happens over time.
Air Pressure and Load Capacity
The load capacity on the chart assumes the tire is inflated to the pressure printed on the tire's sidewall or on a placard on your trailer frame. This pressure is called the "maximum rated pressure" and is usually between 65 and 80 psi for trailer tires, depending on the load range and size.
If you underinflate the tire, the capacity drops. A tire at 60 psi when it should be at 75 psi cannot carry the weight listed on the chart. Underinflated tires also overheat, wear unevenly, and fail suddenly. Check your tire pressure before every trip and whenever the temperature changes significantly.
Do not overinflate beyond the maximum rated pressure printed on the tire. Overinflation does not increase capacity; it only makes the tire ride harshly and wear in the center, shortening its life. Use a quality tire gauge and check pressure when the tires are cold, before the trailer has been driven.
When You Need a Higher Load Range
If your loaded trailer weight exceeds what your current tires can carry, you have two options: reduce the load or upgrade to a higher load range tire. Upgrading means buying new tires in the same size but with a higher letter rating—for example, moving from Load Range D to Load Range E.
Higher load range tires are stiffer and heavier, which affects how your trailer handles. They may require higher air pressure, which you will find on the new tire's sidewall. Some trailers are not designed to handle the stiffer ride of a much higher load range, so check your trailer manufacturer's recommendations before upgrading more than one load range letter.
If you cannot find a higher load range in your current tire size, you may need to go to a larger tire size. A tire shop can advise whether this is possible on your trailer without affecting clearance or speedometer accuracy. This is a bigger change and should be done by someone familiar with your trailer model.
Common Mistakes When Using the Chart
The most common mistake is confusing tire size with load range. Two tires marked ST225/75R15 are the same size, but one might be Load Range D and another Load Range E. Size alone does not tell you capacity. You must check the load range letter on the sidewall.
Another mistake is using the chart for only one tire when your trailer has multiple tires. The capacity on the chart is per tire, not total. Multiply by the number of tires you actually have. A trailer with two tires needs each tire to carry half the total weight; a trailer with four tires splits the weight four ways.
A third mistake is ignoring air pressure. A tire at the wrong pressure does not carry the weight the chart promises. Check pressure monthly and before long trips. Temperature changes affect pressure, so a tire that was correct in summer may be underinflated in winter.
Frequently Asked Questions
Can I use a car tire load range chart for my trailer tires?
No. Trailer tires are marked with "ST" (Special Trailer) and have different construction than car tires. They are stiffer and designed for the specific stresses of towing. Use only the chart for the exact tire size and brand on your trailer. A car tire chart will not match.
What happens if I exceed the load range capacity?
The tire overheats, the sidewall flexes beyond its design limit, and the cord layers separate inside the tire. This causes a blowout, usually without warning. A blowout at highway speed can cause you to lose control of the trailer. This is why load range capacity is a hard limit, not a guideline.
Do I need the same load range on all tires?
No, but you should use the lowest load range on your trailer to calculate your safe weight limit. If three tires are Load Range D and one is Load Range C, use the Load Range C capacity for all four tires in your calculation. Mixing load ranges is not ideal; replace all tires with the same load range when possible.
Where do I find the chart if the tire shop did not give me one?
Visit the tire manufacturer's website and search for your tire size. Most manufacturers publish load range charts as downloadable PDFs. You can also call the tire shop where you bought the tires and ask them to email or print the chart for your specific tire size and brand.
Does load range change as the tire wears?
No. The load range letter and capacity remain the same throughout the tire's life. However, a worn tire is weaker and more prone to failure, so do not wait until tread is nearly gone to replace a trailer tire. Replace trailer tires when tread reaches 4/32 inch, well before they are legally worn out.