Trailer Tire Size – How Big Is It?

Do you need to replace the tires on your trailer? If so, then you should know the exact specification of your trailer’s tires. Choosing an incorrect tire can lead to devastating results, including but not limited to drops in loading capacity and exploding rubber.

Trailer tires typically come in 2 rim size groups—12 inches and under and 13 inches and above.

However, the size of a trailer tire isn’t the other thing you need to consider. In this guide, I’ll break down the various trailer tire sizes and how to decipher the tire code.

Standard Trailer Tire Size

When looking at trailer tire sizes, you will first need to determine the rim’s diameter. That way, you can limit your search to only a specific set of potentially suitable tires.

As previously stated, there are 2 main trailer tire size groups—those that are 12 inches and under and those that are 13 inches and above. The following chart will describe tire sizes, rim widths, and load ranges based on tire sizes.

12 inches and Under

Rim Diameter (in.)	Tire Size (in.)	Rim Width (in.)	Load Capacity (Ply: lbs. @ PSI)	Total Diameter (in.)
8	4.80/4.00-8	3-3/4	B: 590 @ 60 C: 760 @ 90	16.1
8	5.70-8	3-3/4	B: 715 @ 50 C: 910 @ 75 D: 1075 @ 100	18.1
8	165/68-8	5-3/8	C: 800 @ 70	16.5
8	215/60-8	7	C: 935 @ 50 D: 1165 @ 70	18.3
9	6.90/6.00-9	4-1/2	C: 1298 @ 60	21.1
10	205/50-10	6	B: 665 @ 30	18.3
10	205/65-10	6	B: 910 @ 35 C: 1100 @ 50 D: 1300 @ 70 E: 1650 @ 90	20.5
12	4.80-12	4	B: 785 @ 60 C: 990 @ 90	20.5
12	5.30-12	4	B: 840 @ 55 C: 1045 @ 80 D: 1250 @ 105	21.9
12	145/80-12	4	D: 1220 @ 65 E: 1520 @ 80	21.3

13 inches and Above

Rim Diameter (in.)	Tire Size (in.)	Rim Width (in.)	Load Capacity (Ply: lbs. @ PSI)	Total Diameter (in.)
13	175/80-13	4-1/2, 5, 5-1/2	B: 1100 @ 35 C: 1360 @ 50 D: 1610 @ 65	24.1
13	185/80-13	4-1/2, 5, 5-1/2	C: 1480 @ 50 D: 1725 @ 65	24.4
14	205/75-14	5, 5-1/2, 6, 6-1/2	B: 1430 @ 35 C: 1760 @ 50 D: 2100 @ 65	26.3
14	215/75-14	5-1/2, 6, 6-1/2, 7	C: 1870 @ 50	26.7
14.5	8-14.5MH	6	E: 2540 @ 85 G: 3070 @ 116	27.7
15	205/75-15	5, 5-1/2, 6, 6-1/2	B: 1480 @ 35 C: 1820 @ 50 D: 2150 @ 65	27.1
15	225/7515	6, 6-1/2, 7	C: 2150 @ 50 D: 2540 @ 65 E: 2961 @ 90	28.4
15	7.00-15LT	5, 5-12, 6	E: 2403 @ 70	29.4
16	235/80-16	6, 6-1/2, 7, 7-1/2	D: 3000 @ 65 E: 3500 @ 90	30.9
16	235/85-16	6, 6-1/2, 7, 7-1/2	E: 3640 @ 95 F: 3960 @ 110	31.6
16	7.50-16LT	6, 6-1/2, 7, 7-1/2	D: 2590 @ 60 E: 2926 @ 75 F: 3168 @ 85	31.8
17.5	215/75-17.5	6-3/4	H (single): 4805 @ 123 H (double): 4540 @ 123	30.2

Understanding Tire Codes

If you take a look at the writing on the side of a tire, you’ll find that they come with all sorts of hard-to-understand symbols. You’ll also notice how the tires on one vehicle can have vastly different codes or designations to tires on another.

You might find a trailer tire with “LT 215/75 R15 106Q D1 BSW” written on the side.

The symbols refer to the following:

[Service Type][Width]/[Aspect Ratio][Construction][Rim Diameter][Load Index][Speed Rating][Load Range][Extras]

Let’s take a look at each variable individually.

Service Type

This refers to what sort of vehicle the tire can hold up. While there are numerous service types, you only need to pay attention to P (passenger), LT (light truck), and T or TS (trailer).

Width

This figure describes the width of the tire in millimeters. The width is measured by recording the width of a properly inflated tire that is not mounted to a vehicle. When it holds a vehicle or trailer up, the width will expand slightly, so it will not be exactly the same as the nominal width.

Aspect Ratio

This number is used to describe the ratio between the height and width of the tire, not including the wheel. In the example above, “75” would mean the tire has a 75% aspect ratio or that the distance between the tire’s tread to the edge of the rim is 75% of the tire’s nominal width.

Construction

Construction refers to how the tire is made up on the inside. For trailer tires, all you really need to look for in the Construction Code R, which stands for Radial. Bias ply tires also exist, though they are mainly used for commercial purposes, not for consumer trailer applications.

Rim Size

This is the tire seat diameter, not the outer diameter of the rim. What you should take notice of is that nowhere in a tire’s code does it include the width of the rim, which is another important factor to consider.

Load Index

This code describes how much weight a trailer tire, when properly inflated, can carry. In the example provided above, the 106 actually refers to a weight capacity of 2094 pounds. You can check out Tires Plus’ tire load index chart for further information.

Speed Rating

This code describes the maximum speed that a tire can travel. The Q code refers to a maximum speed of 100 miles per hour. Again, check out Tires Plus for their speed rating chart.

Load Range

This is another code that requires a separate chart to understand. It basically describes the minimum and maximum load capacity of the tire. It doesn’t matter as much since the Load Index is sufficient.

Extras

The Extras section of a tire code isn’t as important as the rest since it does not affect the overall performance of a tire. In the example, BSW simply means “Black Side Wall.”