Choosing Trailer Tires – Important Hidden Details To Know

It seems like choosing trailer tires should be easy. Yet, finding the right tires for your situation means deciphering code hidden in plain sight on the sidewall. Get it right, and you will significantly reduce the chances of being stranded along the road.

We have already covered this topic from the standpoint of tire types – “Should I use Trailer Tires, or Automotive Tires?” We also have a solid overview of sizing and selection in – “Wheels And Tires For Your Trailer“.

This article looks at some conflicting constraints in choosing trailer tires (width, height, capacity) and how tire specs impact trailer design, performance, and safety. We also look deeper at the often-missed details of Load Index and Speed Rating.

Most of all, we give you the tables as a Quick Reference Guide for tires, so you have a place to easily find them. Here are the links:

The Load Index Table for tire capacity.
Then, speed decoding with the Speed Rating Table.
And, Tire Size Recommendations (by axle capacity).

When choosing trailer tires, it helps to know the details of Trailer Tire Ratings, and how they may conflict with other trailer priorities.

Understanding Trailer Tire Ratings

Before diving into the engineering details, here are the Trailer Tire Ratings of most importance when choosing trailer tires. These specs appear on the sidewall – sometimes clearly, most times hidden as code.

These 4 apply specifically in this article. These are short definitions. We cover the full code in the article “Wheels And Tires For Your Trailer“.

Tire Size

A combination of width, aspect ratio, construction type, and rim diameter.
– Example: ST 215/75R15 means it is a Trailer tire, 215 mm wide, 75% aspect ratio, radial construction, to fit a 15″ rim.

Load Index

A code NUMBER telling the maximum load a tire can carry at full pressure.
– Example: Load Index 107 = 2150 lbs per tire.
We will talk more about this below. This is the most important rating in matching a tire to trailer axle capacity.

Load Range

A code LETTER indicating the tire’s pressure class. Originally based on bias ply ratings, it is now more about inflation pressure.
– Example: Load Range D = 65 PSI, Load Range E = 80 PSI.
While helpful as a guide, Load Range does not tell a full story. Always check the Load Index and Pressure specs on the tire sidewall.

Speed Rating

A code LETTER indicating the maximum sustained speed a tire can handle.
– Example: Speed Rating M = 81 MPH.
Higher speed ratings usually come with better internal tire construction and heat tolerance.

Decipher the code using the position of the Letter or Number. “Wheels And Tires For Your Trailer” has the full explanation.

Conflicting Constraints When Choosing Trailer Tires

Choosing trailer tires is more than just matching a size. When replacing a tire, the tradeoff is often between fitment (tire size), cost, and correct ratings.

When designing or building a trailer, conflicting constraints come from competing needs – like space, legal limits, and safety. The key is knowing how to balance function, convenience, and space without sacrificing safety.

In general, for trailers we want all the great advantages of wide, tall tires. At the same time, we want all the space advantages of small tires, but without the harshness of a small diameter, and rock hard super high pressure. Here are the areas of conflict as they apply to choosing trailer tires for both new builds and existing trailers.

Tire Width

Wider tires have several advantages – including a larger footprint on the road, often stiffer sidewalls, and usually a higher load capacity. The downside? They take up more horizontal space.

On smaller trailers, added width may simply mean adjusting for clearance to the frame, then using wider fenders to cover the wider tires.

When designing larger trailers where we want to maximize deck width (like a car hauler) – within the legal limit (of 8.5 feet, or 102″) – wide tires create a conflict. Wider tires can mean a narrower deck to stay legal.

For an existing trailer, using wider tires to improve ride quality and capacity, may put you over the legal limit – depending on the trailer design.

Can we just choose narrower tires? Yes, sometimes. However, to maintain capacity . . . well, that brings us to the next constraint: Outside Diameter.

Tire OD (Outside Diameter)

This is a constant battle with trailer design. On the positive side, a larger OD improves how the trailer rolls down the road. It smooths out bumps (just a little), reduces tire RPM at highway speed, increases ground clearance, and helps tires stay cooler under load. Larger diameter tires can have a larger contact patch (depending on many factors) and, when paired with a larger wheel, often carry more weight.

The down sides of a larger OD include: Taller fenders, more space needed around the tire, and a higher deck – which leads to a bunch of cascading effects. We normally want a low deck height for easier loading, better stability, and greater usability. Height affects ramp angles, center of gravity, and access – depending, of course, on the situation. The deck height effect of diameter is amplified for Deck-Over Trailers.

Like many things in trailer design, tire diameter is a tradeoff – often connected with tire width – and the cascading effects of both. But there is one more piece of the puzzle when choosing trailer tires.

Tire Load Carrying Capacity

We use the term “Load Index” as a stand-in for Carrying Capacity. It represents the maximum load a tire can carry. For trailers, this is the least negotiable constraint.

The two above, Tire Width and Tire OD, directly influence Load Index. Generally speaking, we select the tire capacity based on Axle Weight Rating, then lookup the Load Index and pick a tire size with that Index (or higher). Tire capacity being greater than half the axle capacity, since each axle has 2 tires.

Choosing trailer tires becomes a matter of balancing tire size preferences with the required capacity. Heavier trailers need higher Load Index ratings, which usually means larger tires, higher pressures, or both. Unfortunately, we can’t control the specs, so we must choose from available tires.

I hear from customers with frustration in not finding a small tire to support the weight they wish to carry. One example is the desire for small tires under a tiny house to keep the trailer low. They look at the trailer and think, “There is so much room under it, I would rather have that space inside the house!” Yes, smaller tires help height, but we cannot make new specs, or defy physics.

Summary For Choosing Trailer Tires

Choosing trailer tires usually means searching through available options to find the right combination of Trailer Tire Ratings to meet both load and layout goals. This is the conflict.

Yes, choosing trailer tires is a balance of which advantages you value most. What load will you carry? How much space do you need? What tires are available to meet these desires? – Then, what trade-offs are required?

Finding tires of the right “Size” is easy, but finding the “Right” tires to meet the needs is often a quandary. Since carrying capacity is a key factor for trailers, we will take a closer look at Load Index next.

Load Index And Tire Capacity Table

This is a partial table showing the Load Index and what that means for tire load carrying capacity. This is the critical rating when Choosing Trailer Tires.

For our purposes the table below focuses on values most useful for typical trailers. It is trimmed at both ends for clarity. To see a complete list of load index values, please visit the Discount Tire Website.

Recommendations: Load Index Table & Tire Load Capacity

Load Index	Tire Capacity (lbs)	Example Tires	Recommended For This Axle Capacity
80	992	x
81	1019	x
82	1047	x
83	1074	x
84	1102	x
85	1135	x
86	1168	x	2000 Lb.
87	1201	x	2000 Lb.
88	1235	x	2000 Lb.
89	1279	x	2000 Lb.
90	1323	x	2000 Lb.
91	1356	175/80 R13 C	2000 Lb.
92	1389	x	2000 Lb.
93	1433	x	2500 Lb.
94	1477	x	2500 Lb.
95	1521	x	2500 Lb.
96	1565	x	2500 Lb.
97	1609	x	2500 Lb.
98	1653	x	2500 Lb.
99	1709	x	2500 Lb.
100	1764	x	3000 Lb.
101	1819	x	3000 Lb.
102	1874	x	3000 Lb.
103	1929	x	3000 Lb.
104	1984	x	3000 Lb.
105	2039	205/75 R14 D	3500 Lb.
106	2094	215/75 R15 D	3500 Lb.
107	2149	x	3500 Lb.
108	2205	x	3500 Lb.
109	2271	x	3500 Lb.
110	2337	x	4000 Lb.
111	2403	x	4000 Lb.
112	2469	x	4000 Lb.
113	2535	x	4000 Lb.
114	2601	x	4000 Lb.
115	2679	x
116	2756	x
117	2833	x
118	2910	x
119	2998	x	5200 Lb.
120	3086	225/75 R15 F1	5200 Lb.
121	3197	x	5200 Lb.
122	3307	x	5200 Lb.
123	3417	235/80 R16 E1	5200 Lb.
124	3527	225/90 D16 E1 235/80 R16 E1	5200 Lb. 6000 Lb.
125	3638	x	6000 Lb.
126	3748	x	6000 Lb.
127	3858	x	6000 Lb.
128	3968	x	6000 Lb.
129	4079	235/85 R16 G 235/80 R16 G 225/90 R16 G	6000 Lb. 7000 Lb.
130	4189	x	7000 Lb.
131	4289	x	7000 Lb.
132	4409	x	7000 Lb.
133	4541	x	7000 Lb.
134	4674	x
135	4806	215/75 R17.5 H	8000 Lb.
143	6008	235/75 R17.5 H	8000 Lb. 10,000 Lb.

The 3rd column shows some example tires that are useful with trailers.
The 4th column shows common Axle Capacities for which we recommend that Load Index.
Actual tires do not exist for some of these Load Index values. If needed, move to the next higher capacity.

You can think of this as a Quick Reference Guide for matching tire specs to the weight and design needs of your trailer. Please remember – the Load Index only holds if the tire is inflated to its rated pressure.

This chart is a good tool for Choosing Trailer Tires with the right combination of strength, size, and fit. Bookmark this page to refer back when you need tires. Recommendations are discussed below.

Where Do Load Index Numbers Come From?

The Load Index is a standardized number used worldwide to define how much weight a tire can carry. Yet, the values may look a little odd in the USA – because the index is based on metric units.

Each Load Index value corresponds to a specific kilogram (kg) rating, set by international standards. For example:

Load Index 100 = 800 kg = 1764 lbs.

Load Index 120 = 1400 kg = 3086 lbs.

That is why the capacities in pounds seem strange – they are kg values converted to pounds (lbs). While the index numbers make sense in metric, they come out looking arbitrary in pounds.

Why Do You Recommend Tires of More Capacity Than My Axle?

When Choosing Trailer Tires for a given axle, of course, we start with the axle capacity. Each axle has two tires, so logic says each tire will carry half the load. However, that logic misses reality.

– For example, if your axle is rated for 6000 lbs, each tire must carry 3000 lbs, right? 3000 x 2 = 6000. The math is right, but the inputs are incomplete.

In practice, other factors are at play:

Trailers are not always loaded evenly, meaning one side can have more weight than the other.
Trailers are often loaded near or over the limit. Since it is hard to tell, overload is not uncommon.
When cornering, the outside tires experience higher loads due to centrifugal forces.
Bumps in the road increase load on a tire. While this is momentary, it is significant.
With multiple axles, driving on uneven ground (like into a gas station or restaurant driveway) can shift weight and overload on one or more tires.

We recommend choosing trailer tires rated at least 15% over the half the axle capacity – giving you a cushion for real-world conditions. There is no reason to flirt with disaster by running tires at the limit.

The 15% recommendation is what you see in the tables above, and below.

Avoiding Tire Troubles By Choosing Proper Trailer Tires

When it comes to trailer trouble, tires and wheel bearings top the list. Yet, most of the problems are preventable – and often caused by poor tire choices, overload, or neglect.

Avoid problems with these simple choices:

Use tires with 15% more capacity than needed.
Don’t overload the trailer, ever.
Respect the tire speed rating (see below).
Inspect tires regularly to assure proper pressure. (Adjust pressure when appropriate, either for load or for trailer bouncing.)
Replace tires when needed. (Often trailer tires will age-out before they wear-out.)
Service bearings on schedule.

For a few extra dollars, you can avoid hours of frustration and potentially thousands in damage.

Speed Rating – The Silent Safety Spec

Speed Rating is an often-overlooked spec – likely because it hides behind a code letter. I think it is better to state clearly because it matters – a lot – but that is not mine to choose.

The tire salesman is interested in selling his tires in stock, but you get to live with the limits – even if you don’t know what they are! That is scary, so ask.

The Speed Rating is a letter code for the maximum speed a tire is designed to handle under load and at proper pressure. This does not mean the tire will instantly explode if you exceed the speed, but it does significantly increase risk. Hitting a small bump at overspeed can be fatal for the tire.

Here are some Speed Rating codes deciphered (applicable for trailer tires):

G = 56 MPH max.
J = 62 MPH max.
K = 68 MPH max.
L = 75 MPH max.
M = 81 MPH max.
N = 87 MPH max.
P = 93 MPH max.
Q = 100 MPH max.

See the full table at the Discount Tire Website. Gray Values are for reference, Please avoid them.

We recommend Speed Rating N or higher when possible. Never go below L. Plan a margin for safety – especially for a full trailer running on hot pavement. N is sometimes hard to find on ST tires, but it is more common on LT tires, which often have stronger construction and better heat tolerance.

This does not mean you should drive 87 MPH while towing. However, it does mean the tire is built to handle that level of sustained speed, and it is made to a better construction standard.

Tires that exceed their speed rating generate excess heat, which breaks down the internal structure. Unfortunately, it is nearly impossible to see internal damage, so it becomes a time-bomb. Like the load rating, it is best to stay below the speed rating.

A Secondary Effect

Higher speeds increase the risk of trailer sway and other speed related issues. Just because a tire can go 80+ MPH, does not mean your trailer can. For a deeper look see this article about stability and Trailer Sway.

We are not here to scare you about driving at highway speed, but we do want you to be safe. Speed and trailer safety is a bigger discussion, but Choosing Trailer Tires with the proper Speed Rating is part of it. Make sure tires fit your driving habits – not just what is printed on the speed limit sign.

What Tires Do I Recommend For Your Trailer?

Here is a table of tires we recommend – listed by axle capacity. These are just a few I often use. Hopefully they are also available to you, but check your local tire store to be sure. ( As noted in our previous article, both ST and LT variations are fine. )

While all of the above tire sizes are excellent for the listed axle capacity, I did list them in order. For various reasons, which are not the same for every case, the tires for each axle capacity are in order of preferred on top.

Armed with an appropriate range of Load Index values from the table above, then you can choose your trailer tires by width, wheel size, and outside diameter. Again, these are just a few that meet our recommendations. Others are also available.

Conclusion – Important Hidden Details In Choosing Trailer Tires

Choosing trailer tires is not as simple as picking a size and a brand. Every tire has ratings – for load, speed, pressure, and construction – and, the details matter.

While the ratings are usually hidden in code, you now have the tables above to decipher the tire limits. Use the tables – and our recommendations – to know the code, and to help find your next right tires.

Trailer Tire Ratings are perhaps lesser known, but critically important specs for trailer design, performance, and safety. Load Index, Speed Rating, Tire OD, and Width are not just technical details, because they drive real-world results.

If this information helps you make better decisions when Choosing Trailer Tires, then it has done its job. It should certainly relieve some of the trailer towing fears.

You may also want to read or revisit some of these related articles:

If you found this article helpful, bookmark or save the page so you have access to the tire charts when you need them. And if you know someone who pulls a trailer, share this article – it just might save them time, frustration, or worse.

Good luck in choosing your next trailer tires.

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Choosing Trailer Tires – Important Hidden Details