All Terrain Tire Size Guide: How to Read Sizes, Load Ratings, and Fitment

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This article is part of our All-terrain Tires Guide.

Choosing all-terrain tires is not just about tread pattern or brand. The right size, load rating, and overall fitment matter just as much, especially if you want good road manners, safe towing performance, and no rubbing issues after installation.

If the sidewall numbers look confusing, you are not alone. Tire sizing uses a mix of letters and numbers that tell you the tire width, sidewall height, wheel diameter, load capacity, and speed capability. Once you know how to decode those markings, it becomes much easier to compare options and avoid buying the wrong set.

This guide breaks down the basics in plain language for DIY vehicle owners. You will learn how to read common all-terrain tire sizes, what load ratings really mean, how metric and flotation sizes compare, and how to confirm whether a tire will actually fit your truck, SUV, or crossover.

What the Numbers on an All-terrain Tire Mean

Most modern all-terrain tires use either a metric size or a flotation size. Both tell you important fitment information, but they present it differently.

Metric Size Example

A common metric size might look like 265/70R17. Here is how to read it: 265 is the tire width in millimeters, 70 is the aspect ratio or sidewall height as a percentage of the width, R means radial construction, and 17 is the wheel diameter in inches.

• 265 = section width in millimeters
• 70 = sidewall height is 70% of the tire width
• R = radial tire construction
• 17 = wheel diameter in inches

Flotation Size Example

A flotation size might look like 31×10.50R15LT. In this format, 31 is the overall tire diameter in inches, 10.50 is the tire width in inches, R still means radial construction, 15 is the wheel diameter in inches, and LT indicates a light truck tire.

• 31 = approximate overall tire height in inches
• 10.50 = approximate tire width in inches
• 15 = wheel diameter in inches
• LT = light truck service classification

Metric sizing is more common on newer vehicles, while flotation sizes are still popular on older trucks, Jeeps, and off-road builds. If you are replacing the factory tire size, start by matching the original format unless you have already confirmed an alternative size will fit.

How Width, Sidewall Height, and Diameter Affect Fitment

A tire is not just one measurement. Changing width, aspect ratio, or overall diameter can affect clearance at the fenders, suspension, inner wheel wells, and steering components. Even a size that seems close on paper can create rubbing under turns or suspension compression.

Tire Width

Wider tires can improve footprint and give a more aggressive look, but they also need enough room between the tire and the suspension, frame, and fender liner. Wheel width and wheel offset also play a major role in whether a wider all-terrain tire will fit cleanly.

Aspect Ratio

The aspect ratio affects sidewall height. A taller sidewall often improves ride comfort and off-road compliance, while a shorter sidewall usually sharpens steering feel on pavement. Changing this number also changes total tire diameter.

Overall Diameter

Larger-diameter tires increase ground clearance, but they can also reduce effective gearing, change speedometer accuracy, and make acceleration feel slightly slower. They are also more likely to rub during full steering lock or when the suspension compresses over bumps.

• A taller tire can improve obstacle clearance off-road
• A wider tire may require different wheel offset or trimming
• A larger overall diameter can affect speedometer and odometer readings
• Big size jumps may impact towing performance and braking feel

What Load Index and Load Range Really Mean

Load capacity is one of the most important parts of tire selection, especially on trucks and SUVs that carry cargo, tow, or spend time on rough surfaces. You need a tire that can safely support the vehicle’s weight under real operating conditions.

Load Index

The load index is a numerical code that tells you how much weight one tire can support at its rated pressure. For example, a tire marked 114 can carry more weight than a tire marked 110. You should never choose a tire with a lower load index than your vehicle requires.

Load Range

On many all-terrain light truck tires, you will also see a load range such as C, D, or E. This indicates the tire’s strength and maximum inflation capability. In general, higher load ranges have stronger construction and can support heavier loads, but they may also ride firmer.

• Load Range C is often used on lighter trucks and SUVs
• Load Range D offers more carrying capacity and stiffer construction
• Load Range E is common for heavier-duty pickups, towing, and hauling

Do not assume that a heavier-duty tire is always better. A very stiff load range on a lighter vehicle can reduce ride comfort and may not be necessary if you do little towing or hauling. Match the tire to how the vehicle is actually used.

How to Read Speed Rating and Service Description

After the size, you may see a service description such as 112T or 121/118S. This combines the load index and speed rating.

Speed Rating

The speed rating is a letter that indicates the maximum speed capability of the tire under specified conditions. For all-terrain tires, common ratings include S, T, and sometimes Q or R depending on the design.

For most drivers, the key point is not top speed. It is whether the tire meets the vehicle manufacturer’s requirements for safe operation. If your original tires have a certain minimum speed rating, do not drop below it unless you have verified that the replacement is appropriate for your application.

• The number in the service description is the load index
• The letter is the speed rating
• LT tires may show dual load indexes for single and dual wheel applications

P-metric, LT, and Flotation Tires: Which Type Should You Choose?

The letters before or after a tire size matter. They tell you what kind of service the tire is designed for, and that affects durability, ride quality, and carrying capacity.

P-metric Tires

A size like P265/70R17 is a passenger-rated tire. Many SUVs and crossovers use P-metric all-terrain tires because they are lighter, often quieter, and typically ride more comfortably on pavement.

LT Tires

A size like LT265/70R17 is a light truck tire. LT tires usually have stronger sidewalls and higher load capacity, making them a better fit for pickups, heavily loaded SUVs, towing, overlanding, and rougher off-road use.

Flotation Tires

Flotation sizes such as 33×12.50R17LT are common on modified trucks and Jeeps. They are easy to understand at a glance because they list overall height and width in inches, but you still need to verify exact dimensions by brand and model because actual measurements can vary.

• Choose P-metric for daily driving comfort and lighter-duty use
• Choose LT for towing, hauling, stronger sidewalls, and more abuse resistance
• Choose flotation sizes when your wheel and suspension setup is designed around inch-based sizing

How to Know if a Bigger All-terrain Tire Will Fit

Many owners want to size up for a tougher look and more ground clearance. That can work well, but fitment depends on more than just the tire size printed on the sidewall.

• Current wheel diameter and width
• Wheel offset or backspacing
• Stock suspension height versus leveled or lifted setup
• Available clearance at the fender liner, upper control arm, strut, and frame
• Whether the vehicle is 2WD or 4WD
• Brake package size and steering geometry

Even two tires with the same labeled size can measure differently from one manufacturer to another. Tread design, sidewall shape, and actual section width can all vary. That is why checking the manufacturer’s published dimensions is smarter than relying only on the nominal size.

A Safe Way to Size Up

A modest increase in overall diameter is often easier to fit than a major jump in both height and width. If you want to go larger, compare the new tire’s actual mounted diameter and section width to your current tire and review known fitment data for your exact vehicle generation, trim, and wheel setup.

Important Fitment Checks Before You Buy

Before ordering all-terrain tires, confirm the basic specs on your door jamb sticker, owner’s manual, and current tire sidewall. Then verify that the replacement matches your vehicle’s real-world needs.

1. Check the factory tire size and wheel diameter.
2. Confirm the minimum required load index and speed rating.
3. Make sure the tire matches your wheel width range.
4. Verify actual diameter and section width, not just the listed size.
5. Consider whether you tow, haul, or drive off-road often enough to justify LT construction.
6. Account for lift kits, leveling kits, spacers, aftermarket wheels, and offset changes.
7. Check for snow-service needs such as the Three-Peak Mountain Snowflake symbol if winter traction matters in your area.

If you plan to reuse your existing spare, make sure its diameter is still compatible with the new set. A major difference in size can be a problem on 4WD and AWD vehicles if you need to run the spare for any distance.

Mistakes to Avoid when Choosing All-terrain Tire Sizes

The wrong tire choice can lead to poor drivability, extra noise, rubbing, uneven wear, or reduced towing confidence. A few common mistakes cause most fitment problems.

• Choosing a size based only on appearance without checking actual dimensions
• Ignoring wheel offset and backspacing
• Dropping below the required load index or speed rating
• Assuming every tire in the same labeled size measures the same
• Buying an overly heavy E-load tire for a light daily driver with no towing demands
• Forgetting that larger tires may affect gearing, fuel economy, and braking feel
• Skipping an alignment after suspension or wheel changes

If you are between two sizes, the best option is usually the one that fits cleanly with the fewest compromises. A tire that clears properly and matches your vehicle’s load needs will perform better than a bigger tire that creates constant rubbing or handling issues.

Quick Buyer Checklist for the Right All-terrain Tire

Use this checklist to narrow down your choices before you buy.

• Match the correct wheel diameter
• Choose a size that clears at full lock and suspension travel
• Meet or exceed the factory load index requirement
• Keep the appropriate speed rating for your vehicle
• Pick P-metric or LT construction based on actual use, not just looks
• Review manufacturer spec sheets for real diameter, width, and approved wheel range
• Consider road noise, winter performance, tread life, and wet traction along with off-road grip

For most DIY owners, the best all-terrain tire is the one that balances fitment, load capacity, and daily drivability. Start with the vehicle requirements, then choose the tread and construction that fit how you actually drive.

Related Maintenance & Repair Guides

• When to Replace All Terrain Tires: Tread Depth, Age, and Wear Patterns
• How Much Do All Terrain Tires Cost to Replace? Real-World Price Ranges
• How to Choose All Terrain Tires for Your Truck or SUV
• Signs Your All Terrain Tires Need Replacement: Noise, Vibration, and Tread Damage
• Cheap All Terrain Tires: When Saving Money Is a Good Idea – And When It Isn’t

Related Buying Guides

Check out the All-terrain Tires Buying Guides

FAQ

Can I Put Larger All-terrain Tires on a Stock Truck or SUV?

Sometimes, yes, but it depends on available clearance, wheel offset, suspension height, and the actual dimensions of the tire. A small size increase may fit, while a larger jump can cause rubbing at the fenders, frame, or suspension.

What Is the Difference Between P-metric and LT All-terrain Tires?

P-metric tires are passenger-rated and usually offer a smoother, lighter ride for daily driving. LT tires are built for heavier-duty use, with stronger construction and higher load capacity for towing, hauling, and rougher off-road conditions.

Do All Tires with the Same Listed Size Measure Exactly the Same?

No. Actual diameter, section width, tread width, and sidewall shape can vary by manufacturer and tire model. Always check the published specifications before buying.

How Do I Know What Load Rating My Vehicle Needs?

Check the driver’s door jamb sticker, owner’s manual, or original-equipment tire information. The replacement tire should meet or exceed the vehicle’s required load capacity.

Will Bigger All-terrain Tires Affect Fuel Economy?

They often can. Larger and heavier tires may increase rolling resistance and rotational mass, which can reduce fuel economy and slightly change acceleration and braking feel.

What Does the LT Marking on the Sidewall Mean?

LT stands for light truck. It indicates the tire is designed for heavier-duty service than a typical passenger-rated tire, often with higher load capacity and stronger sidewalls.

Is Load Range E Always the Best Choice for All-terrain Tires?

Not always. Load range E is useful for heavier trucks and towing, but on a lighter daily driver it can produce a firmer ride and unnecessary extra weight. Choose the load range that matches your vehicle and usage.

Want the full breakdown on All-terrain Tires - from costs and replacement timing to DIY tips and how to choose the right option? Head over to the complete All-terrain Tires guide.