Measuring a Trailer Tire

trailer tire size

Each trailer tire has a size branded to its sidewall. This size lists valuable information about your tire. The seven pieces of information that a tire size may contain are the following:

  1. Application Type
  2. Section Width
  3. Aspect Ratio
  4. Internal Construction
  5. Wheel Diameter
  6. Load Range
  7. Service Description
    • Includes Load Index and Speed Rating

Writing Tire Sizes

There are three conventions for writing tire sizes. Each method includes some or all of the information mentioned above.

  1. Metric: This way of writing tire sizes contains the most information about the tire; an example is ST175/80-R13 LRD.
    • Includes the application type, section width, aspect ratio, tire construction, rim diameter and load range
  2. Numeric: This is the most common way of writing small trailer tire sizes; an example is 4.80 X 12B.
    • Includes the section width, rim diameter and load range
  3. Alpha Numeric: This method is not used on any of the tires we sell; an example is B80 X 15D.
    • Includes the aspect ratio, rim diameter and load range

1. Application Type

The application type indicates what the tire is intended to be used for.

Note: When replacing trailer tires, we recommend using Special Trailer (ST) tires.

2. Section Width

section width of trailer tire

The section width refers to the distance from the widest point of a tire's outer sidewall to the widest point of its inner sidewall; this distance is measured once the tire is mounted on the wheel it is going to be used with.

3. Aspect Ratio

section height of trailer tire

Sidewall aspect ratio (or section height) is the ratio of the tire height and width that will tell you the tire's section height.

4. Internal Construction

Internal construction refers to how a tire is made. The letters below indicate the possible internal constructions a tire can have.

rim diameter

Note: For everyday use, tires with different internal construction cannot be used together.

5. Wheel Diameter

Wheel (or rim) diameter refers to the diameter of the wheel the tire is mounted on.

6. Load Range

The load range indicates the horizontal and sidewall strength of a tire. It is represented by a letter within each tire size. Each load range letter correlates to a specific number of tire plies and a load pressure in psi units. Sometimes the load range is left off the tire size and is branded on the tire elsewhere.

The information below tells you the ply rating and load pressure (in psi units) for each load range for Special Trailer (ST) and Light-Truck (LT) service tires.

Note: The weight capacity at a certain unit of psi for each tire is branded on each tire. It may be listed under the tire size or somewhere else on the tire.

7. Service Description

The service description includes the load index and speed rating. Only Passenger (P-metric) tire sizes include the service description.

Questions and Comments about this Article


I have a 5x8 foot trailer with 205/65 R 15 Can I use a 205/70 R15 as a spare tire? Thanks 98737

Reply from Jon G.

@Favid You always want to use the exact same tire all around your trailer - including your spare. You might be able to use it to hobble along for like a mile to an exit or tire shop but I would get the exact same tire because with my luck I'd need to use the spare when I'm out in the middle of nowhere. 73369

Dale M.

I have a small trailer that I fitted with new tires, 4.80-8. I kept one of the old tires to use as a spare, but don't know what to look for in a wheel. The current wheels don't have lug nuts, they're held on by a cotter pin/castle nut. What do I measure on my current rims so I can get something that fits? 98533

Reply from Jon G.

You have an older trailer as that style of spindle/wheel isn't really around anymore. I'd look for places that specialize in replacement parts for old trailers if you want that exact wheel. Otherwise you're looking at replacing the axle on your trailer so that you have a more up to date spindle. 73368

Dryhten C.

I was given a trailer and it's in serious need of tires and rims. One is bent. one of the tire walls reads. "5.30/4.5-12" What does this mean? I measured the distance from center to center of the lug nuts and that's 4". 97411

Reply from Jon G.

That means you need a 5.30-12 size tire. If your wheels have a 4-bolt pattern then I recommend part # AM30850 , otherwise you need the Taskmaster # AT53012R45SM with the 5 bolt pattern. 72810


The numbers on my trailer tyre read 5.3-12 so what size spare do I look for? 96266

Reply from Jon G.

You will want to use a 5.30-12 size spare tire. Here is a link to our selection that you can choose from. You'll want to make sure that the bolt pattern on the wheel and the load range on the tire match what you currently have. 71077

Bill P.

So, if I have a ST 205/75 R14 and I'm looking for tire covers, what size do I get (14, 15, 16, etc.)?? 84624

Reply from Chris R.

Your ST205/75R14 tires have an overall diameter of JUST barely over 26", so I highly recommend the Classic Accessories # 052963762402 . 67781

Tom M.

have old boat trailer with 6.9-9 n 84 Carlisle USA trail tire 21" in diameter . Believe the rims are 10.5 " in diameter.They are on a 5 on 4 1/2 bolt pattern for a gator Trailer . need help in finding a replacement tire and wheel . Thank you 76212

Reply from Chris R.

The modern 6.90/6.00-9 trailer tire size is the right replacement for your 6.9-9 units. This is essentially the same size - it just went through a change in how its labeled over the years. The Kenda # AM10040 will work perfectly and for the corresponding wheel we have the Americana # AM20038 . 62231

Jay T.

I’ve got a small older boat trailer and what I can read on the tires are E 4.80- 4.70. Is that correct for a tire size. 75780

Reply from Chris R.

I believe you have a 4.80/4.00 tire like the Kenda Loadstar # AM10002 . I haven't seen it printed quite like what you saw on your particular tire, though. A 4.80/4.00 tire has an overall diameter/height of around 16.1" and a width of 4.6". You could compare these dimensions to your existing tire to be sure. 61918

Bob W.

What is the difference between 5on5 and 5on4 1/2? I understand the first 5 stands for 5 lugs. Is the second # the distance apart? 72203

Reply from Chris R.

You got it. The second number has to do with the actual pattern of the bolts in terms of their separation. There are a few different methods you can use to measure the pattern on a 5 bolt wheel and the article linked below does great job of going over them. 59212



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