OTR Tyres Classification Codes for Earthmovers, Loaders, and Graders

Introduction

Buying OTR tyres without understanding classification codes is like ordering spare parts blindfolded. You might get lucky, but more often you end up with a tyre that overheats, wears unevenly, or fails before its time. The OTR tyres classification codes for earthmovers, loaders, and graders determine load capacity, speed rating, and application fit — get them wrong and you are looking at downtime that costs far more than the tyre itself.

This guide breaks down the alphanumeric system used across the industry, explains how to match codes to specific machines, and shows you how to avoid the costly mismatches that plague many mining and construction operations. Whether you run a fleet of 20-tonne haul trucks or a single motor grader, understanding these codes will help you spec the right rubber the first time.

Key Takeaways

OTR tyre codes combine width, aspect ratio, construction, rim diameter, load index, and speed symbol into one string
Load index numbers translate directly to kilograms per tyre at a defined inflation pressure
Speed symbols for OTR applications rarely exceed 50 km/h, but they still matter for heat generation
Matching codes to machine type prevents sidewall damage, tread separation, and premature failure
Always cross-reference the tyre code with the equipment manufacturer's recommended inflation pressure

What You Need Before Starting

Before you decode any OTR tyre marking, gather three things: the machine's operator manual, the current tyre sidewall information, and the load chart for your specific application. The operator manual lists the original equipment tyre size and load index. The sidewall shows what is actually mounted. The load chart tells you what each axle carries under real working conditions.

You also need to understand the basic anatomy of a tyre code. A typical OTR size reads like this: 29.5R25. The first number is the nominal section width in inches, the letter indicates radial construction, and the final number is the rim diameter in inches. Bias-ply tyres use a dash instead of the R, such as 29.5-25.

For earthmover tyres, you will also encounter codes like 40.00R57 or 27.00R49. These larger sizes follow the same logic but require heavier-duty rims and higher inflation pressures. If you are running a loader or grader, your sizes will typically fall between 17.5R25 and 35/65R33. Before you start, make sure you have access to the Tire Education resources on your tyre supplier's website — they often publish load and inflation tables that are not printed on the sidewall.

Step 1 — Decode the Size and Construction Designation

What to Do

Read the full size marking from the sidewall, for example 23.5R25 or 17.5-25
Identify the construction type: R for radial, dash for bias-ply
Note the rim diameter in inches — this must match your machine's rim exactly
Record the full code including load index and speed symbol, which appear after the rim diameter

Why This Matters

The size designation determines whether the tyre physically fits your machine. A 23.5R25 tyre has a nominal width of 23.5 inches and fits a 25-inch rim. The radial construction means the ply cords run perpendicular to the direction of travel, which generates less heat at higher speeds and provides better traction on hard surfaces. Bias-ply tyres have cords running diagonally, offering a stiffer sidewall that resists cuts better in rocky conditions but runs hotter at speed.

For earthmovers, loaders, and graders, the construction choice affects more than ride comfort. Radial tyres typically deliver 10-15% longer tread life in haul-road applications, according to industry testing data. Bias tyres still dominate in severe rock applications where sidewall cut resistance is the priority. Your application determines which construction suits you.

Common Mistakes to Avoid

Assuming the rim size from the machine model: Always verify the rim diameter stamped on the wheel itself. A 25-inch rim will not accept a 24-inch tyre even if the bolt pattern matches.
Ignoring the load index: The size alone does not tell you how much weight the tyre can carry. Two tyres with identical dimensions can have different load indices and therefore different maximum loads.
Mixing radial and bias on the same axle: This causes uneven wear, handling instability, and can overheat the bias tyre. Never mix constructions on the same machine.

Step 2 — Interpret the Load Index and Speed Symbol

What to Do

Locate the load index number, which appears after the rim diameter, such as the "184" in 23.5R25 184A2
Convert the load index to kilograms using the standard load index table published by the Tire and Rim Association
Check the speed symbol — for OTR tyres this is typically A2 (10 km/h), A4 (40 km/h), or B (50 km/h)
Multiply the per-tyre load by the number of tyres on the axle and compare with your actual axle load

Why This Matters

The load index is a two- or three-digit number that corresponds to a specific load capacity. For example, load index 184 equals 8,000 kg per tyre at the reference inflation pressure. Load index 200 equals 14,000 kg. The speed symbol tells you the maximum speed at which that load can be carried continuously. An A2 rating means 10 km/h; an A4 means 40 km/h. Exceeding either rating accelerates heat buildup and can cause tread separation.

For a 50-tonne haul truck with four tyres, each tyre must carry roughly 12,500 kg. That requires a load index of at least 193, which corresponds to 10,000 kg, or higher depending on the safety margin your operation demands. Loaders and graders typically operate at lower speeds, so the speed symbol matters less than the load index — but it still affects heat generation during long cycles.

Common Mistakes to Avoid

Using the load index from a different tyre size: Load indices are specific to each size and construction. You cannot transfer a load rating from a 17.5R25 to a 23.5R25.
Ignoring the speed symbol for haul trucks: A tyre rated A2 can overheat if your haul road allows 30 km/h. Match the speed symbol to your actual operating speed.
Forgetting inflation pressure adjustments: The load index assumes a specific inflation pressure. Lower pressure reduces load capacity; higher pressure increases it but reduces ride comfort and traction.

Step 3 — Match Codes to Machine Type

What to Do

For rigid dump trucks, select tyres with load indices that cover the fully loaded axle weight plus a 10-15% safety margin
For articulated haulers, prioritize tyres with higher speed ratings since these machines often travel faster on public roads
For wheel loaders, choose tyres with reinforced sidewalls and deeper tread patterns to handle scooping forces
For motor graders, select tyres with a narrower profile and higher speed rating for finish work

Why This Matters

Each machine type imposes different stresses on the tyre. Earthmovers — the rigid dump trucks and articulated haulers — carry massive loads at moderate speeds over haul roads. Their tyres need high load indices and heat-resistant compounds. Loaders generate high torque at low speed, twisting the sidewall during scooping operations. Their tyres need reinforced sidewalls and cut-resistant tread compounds. Graders operate at higher speeds but lower loads, requiring tyres that run cool and provide stable steering response.

The OTR tyres classification codes for earthmovers, loaders, and graders reflect these differences. A loader tyre like a 23.5R25 with an L-5 tread designation has a deep, non-directional tread for rock service. A grader tyre like a 14.00R24 with a G-2 tread designation has a shallower, directional tread for finish grading. The tread designation letter and number tell you the application and tread depth — L for loader, G for grader, E for earthmover, and the number indicates tread depth from 1 (shallowest) to 5 (deepest).

Common Mistakes to Avoid

Using a haul truck tyre on a loader: The tread pattern and sidewall construction are wrong for scooping forces. You will see premature sidewall failure.
Using a grader tyre on a haul truck: The load index is too low, and the tread will overheat under sustained heavy loads.
Ignoring tread depth codes: An L-5 tyre has roughly twice the tread depth of an L-3. Deeper tread lasts longer in abrasive conditions but runs hotter at speed.

Step 4 — Verify Inflation Pressure and Load Compatibility

What to Do

Consult the load and inflation table for your specific tyre size and load index
Determine the cold inflation pressure that corresponds to your actual axle load
Check that the rim width matches the tyre's approved rim range
Record the pressure and check it daily with a calibrated gauge

Why This Matters

Inflation pressure is the single most important factor in OTR tyre life. Underinflation causes excessive flexing, heat buildup, and tread wear at the shoulders. Overinflation reduces the footprint, causing center wear and increasing the risk of impact breaks. The load and inflation table tells you the exact pressure needed for your load. For example, a 23.5R25 tyre with load index 184 requires approximately 525 kPa (76 psi) to carry 8,000 kg. Drop the pressure to 450 kPa and the load capacity falls to roughly 7,000 kg.

For earthmover tyres, the relationship between pressure and load is not linear. A 10% reduction in pressure can reduce load capacity by 8-12%, depending on the tyre construction. That is why daily pressure checks matter — a slow leak that drops pressure by 50 kPa can reduce your safety margin significantly.

Common Mistakes to Avoid

Setting pressure by feel or habit: Always use the load and inflation table for your specific tyre. What worked for the previous tyre brand may not apply.
Ignoring temperature effects: Cold inflation pressure should be checked before the machine starts work. Hot pressure readings run 15-20% higher and should not be used for adjustment.
Using the wrong rim width: A rim that is too narrow or too wide changes the tyre's shape and load distribution. Check the rim width against the tyre manufacturer's approved range.

Step 5 — Document and Monitor Tyre Performance

What to Do

Create a tyre register that records size, load index, speed symbol, and serial number for each tyre
Log inflation pressures weekly and tread depth measurements monthly
Track hours of service and note any unusual wear patterns
Review the data quarterly to identify recurring issues

Why This Matters

Documentation turns tyre management from guesswork into a measurable process. A tyre register helps you spot patterns — for example, if the front tyres on your loaders consistently wear 20% faster than the rears, you may have an alignment issue or an incorrect pressure setting. Tracking tread depth tells you when to rotate tyres or plan replacements before failure. The data also helps you compare tyre brands and models under identical operating conditions.

For fleets running multiple sites, documentation is essential for budgeting. OTR tyres for earthmovers can cost anywhere from $5,000 to $50,000 each, depending on size and specification. Knowing your average tyre life in hours lets you calculate cost per hour and make informed purchasing decisions. It also helps you justify premium tyres if they deliver longer life in your specific application.

Common Mistakes to Avoid

Skipping the data collection: Without records, you cannot identify problems until they become failures.
Comparing tyres across different applications: A tyre that lasts 4,000 hours in soft overburden may only last 2,500 hours in abrasive granite. Compare like-for-like.
Ignoring serial numbers: The serial number tracks the tyre's manufacturing date and batch. If you have a premature failure, the serial number is essential for warranty claims.

Pro Tips for Success

Run the highest load index that fits your rim: A higher load index gives you more margin for overloaded conditions and allows lower inflation pressures for better traction.
Use the speed symbol as a heat indicator: If your haul roads allow speeds above 40 km/h, select tyres rated B (50 km/h) even if your average speed is lower. The margin protects you during downhill runs.
Match tread depth to your cycle: Deep treads like L-5 last longer in abrasive loading but generate more heat. If your cycle includes long hauls, consider an L-4 instead.
Check pressures on all tyres, not just the drive axle: Steering and trailing tyres run at different loads and pressures. Set each position according to its actual load.
Consider the full lifecycle cost: A premium tyre may cost 20% more but deliver 30% longer life. Calculate cost per hour, not purchase price.

For long-haul applications that extend beyond the mine site, the same principles apply to your highway fleet. A Long Haul Tyre with the right load index and speed rating will deliver the same benefits on asphalt as an OTR tyre does on haul roads — longer life, lower fuel consumption, and fewer roadside failures.

Frequently Asked Questions

What does the "R" mean in an OTR tyre size like 23.5R25?

The "R" indicates radial construction, meaning the ply cords run at 90 degrees to the direction of travel. Radial tyres generate less heat at speed, provide better traction, and typically deliver longer tread life than bias-ply tyres. Bias-ply tyres use a dash instead, such as 23.5-25, and offer stiffer sidewalls that resist cuts better in severe rock conditions.

How do I convert a load index to actual kilograms?

Each load index number corresponds to a specific load capacity defined by the Tire and Rim Association. For example, load index 184 equals 8,000 kg, index 193 equals 10,000 kg, and index 200 equals 14,000 kg. You can find the full conversion table in the TRA Yearbook or on most tyre manufacturer websites. Always use the table specific to your tyre's construction and size.

Can I use a loader tyre on a motor grader?

Technically the size may fit, but the tread pattern and construction are wrong. Loader tyres have deep, non-directional treads for scooping and high torque. Grader tyres have shallower, directional treads for finish work and higher speed operation. Using a loader tyre on a grader will cause excessive heat buildup and rapid tread wear. Always match the tread designation to the machine type.

What is the difference between L-3, L-4, and L-5 tread codes?

These codes indicate tread depth for loader tyres. L-3 is a standard depth for general loading, L-4 has 25% deeper tread for more abrasive conditions, and L-5 has 50% deeper tread for severe rock service. Deeper treads last longer in abrasive conditions but run hotter and reduce speed capability. Choose the depth based on your cycle time and surface abrasiveness.

How often should I check inflation pressure on OTR tyres?

Check cold inflation pressure daily before the machine starts work. A drop of more than 10% from the recommended pressure indicates a leak that needs investigation. Hot pressure readings, taken after operation, run 15-20% higher and should not be used for adjustment. For tyres on standby equipment, check pressures weekly since slow leaks can develop even when the machine is parked.

Conclusion

The OTR tyres classification codes for earthmovers, loaders, and graders are not bureaucratic noise — they are the engineering specifications that keep your machines running safely and productively. By decoding the size, construction, load index, speed symbol, and tread designation, you can select tyres that match your application, set correct inflation pressures, and avoid the failures that plague mismatched operations.

Start by auditing your current fleet. Record every tyre's full sidewall marking, compare it with the machine manufacturer's recommendations, and verify that inflation pressures match the load and inflation tables. If you find mismatches, correct them before they cost you downtime. For deeper technical guidance, the LM/R/SC 326 product page and the broader product documentation on your supplier's site provide load tables and application data that go beyond what is printed on the sidewall.

The approach works because it is grounded in measurable data — load indices, inflation pressures, tread depths, and operating speeds. Apply it consistently, and you will see longer tyre life, fewer failures, and lower cost per hour across your entire fleet.