Guide · Vehicles and vehicle parts
How to read OTR tyre sizesand TRA codes.
An OTR tyre size such as 23.5R25 gives the section width in inches, the construction (R for radial, a dash for bias) and the rim diameter in inches. The TRA code beside it, such as E4 or L5, tells you which machine the tyre is built for and how deep its tread is. Together with the star or ply rating, these markings decide whether a tyre fits the machine, carries the load and lasts on the site.
Size formats
Six waysa size is written.
Whatever the format, the last number is the rim diameter in inches.
| Format | Example | How to read it |
|---|---|---|
| Conventional bias (narrow base) | 18.00-25 | 18.00 inch section width, bias construction (the dash), 25 inch rim; aspect ratio around 95 |
| Conventional radial | 18.00R25 | The same size in radial construction (the R) |
| Wide base | 23.5-25 or 23.5R25 | Sizes ending in .5 are wide base: 23.5 inch section width, 25 inch rim, aspect ratio around 80 |
| Metric | 505/95R25 | 505 mm section width, aspect ratio 95 (sidewall height is 95% of the width), radial, 25 inch rim; the metric name of 18.00R25 |
| Low profile, 65 series | 35/65R33 or 750/65R25 | Section width in inches or mm, aspect ratio 65, rim in inches; a wider, lower tyre, common on large loaders |
| Large mining, 80 series | 50/80R57 | 50 inch section width, aspect ratio 80, radial, 57 inch rim; used on large haul trucks |
Equivalent sizes
Inch and metric namesfor the same tyre.
Many radial sizes carry both names. These pairs appear in our OTR tyre catalogue.
| Inch size | Metric equivalent | Series |
|---|---|---|
| 14.00R24 | 385/95R24 | 95 |
| 16.00R25 | 445/95R25 | 95 |
| 18.00R25 | 505/95R25 | 95 |
| 17.5R25 | 445/80R25 | 80 |
| 20.5R25 | 525/80R25 | 80 |
TRA service codes
The letter is the machine,the number is the tread.
The Tire and Rim Association (TRA) code joins a letter for the type of service with a number for the tread type and depth. It is written with or without a hyphen: E4 and E-4 mean the same.
| Code | Service | Tread |
|---|---|---|
| E1 | Earthmover haulage: dump trucks, scrapers, articulated haulers | Rib |
| E2 | Earthmover haulage | Traction |
| E3 | Earthmover haulage | Rock, regular depth |
| E4 | Earthmover haulage | Rock, deep tread |
| E7 | Earthmover haulage | Flotation, for sand and soft ground |
| L2 | Loader and dozer | Traction |
| L3 | Loader and dozer | Rock, regular depth |
| L4 | Loader and dozer | Rock, deep tread |
| L5 | Loader and dozer | Rock, extra deep tread |
| L3S, L4S, L5S | Loader and dozer | Smooth (no pattern) in the same depth class; common underground |
| G1, G2, G3 | Grader | Rib, traction, rock |
| C1, C2 | Compactor | Smooth, grooved |
| IND | Industrial: port, terminal and industrial machines | The number after it (IND-3, IND-4, IND-5) marks the tread class |
| R, F, I | Agricultural drive, front and implement tyres | For example R-1 (drive), R-4 (industrial tractor), F-2 (front), I-1 (implement) |
Tread depth
Regular, deepand extra deep.
TRA groups tread depth into three classes. The deep and extra deep figures are typical multiples of the regular depth for the same size. Markings such as E3+ or L3+ are not TRA classes, so compare the tread depth in millimetres.
| Class | Codes | Typical depth | Where it is used |
|---|---|---|---|
| Regular | E1, E2, E3, L2, L3, G1 to G3 | The base depth for the size | General earthmoving, quarries, loaders on mixed ground |
| Deep | E4, L4 | About 1.5 times regular | Rock, cuts and abrasion, longer wear life where heat allows |
| Extra deep | L5, L5S | About 2.5 times regular | Loaders and dozers in rock and underground, at low speed |
Load strength
Stars, ply ratingand TT or TL.
Ply rating (PR) is used on bias tyres. It is an index of casing strength, not a count of real plies: a 28 PR tyre does not necessarily have 28 plies. A higher PR lets the tyre carry more load at a higher inflation pressure.
Stars are used on radial OTR tyres, typically one, two or three stars, printed as star symbols on the sidewall. Each star rating links to a load and inflation table: more stars, more load at a higher pressure. Always read the star or PR together with the size, because the same rating carries a different load on a different size.
TT or TL marks a tube type or tubeless tyre. In our catalogue each pattern shows its construction, TRA code, stars or PR and TT or TL, and each size lists the load and speed index (for example 201A2, where A2 means 10 km/h), load in kg, pressure in bar, rim, outside diameter, section width and tread depth. For other tyres and parts, see Vehicles and vehicle parts; for how a request moves forward, see how BGI works.
Bias or radial
Two constructions,different strengths.
| Point | Bias (cross-ply) | Radial (all steel) |
|---|---|---|
| Casing | Textile plies laid at an angle, crossing each other | A steel cord ply running straight from bead to bead, under steel belts |
| Load marking | Ply rating (PR) | Stars |
| Sidewall | Thick and stiff; resists cuts and impacts | Flexible; more exposed to sidewall cuts |
| Footprint | Smaller and rounder | Wider and flatter; more traction and flotation |
| Heat build-up | Higher; suits short hauls and low speeds | Lower; higher TKPH for longer, faster hauls |
| Typical use | Short cycle loaders, rough sites, intermittent work | Haul trucks, long cycles, most modern mining and earthmoving fleets |
Heat load
TKPH and TMPH:will the tyre overheat?
Every tyre turns part of its work into heat. TKPH (tonne kilometre per hour) is the heat load capacity of a tyre; TMPH (ton mile per hour) is the same idea in tons and miles. If the working TKPH of the site is higher than the rating of the tyre, the rubber overheats and the tread can separate from the casing.
Site TKPH = mean tyre load (t) × average working speed (km/h). The mean tyre load is the average of the empty and loaded load on the tyre. The average working speed is the round trip distance times the number of trips in a shift, divided by the hours in the shift, stops included. Long hauls and hot climates need correction factors set by the tyre maker. Choose a tyre whose TKPH rating is above the corrected site value; a deeper tread usually means a lower rating.
Your checklist
What to put inyour request.
- 01Machine make and model, and the wheel position (front or rear, steer or drive)
- 02Tyre size as marked on the tyre, inch or metric
- 03TRA code and tread depth class, for example E4, L5 or L5S
- 04Construction (bias or radial), and stars or PR
- 05Load and speed index, TT or TL
- 06Site conditions: haul length, speed, rock or soft ground, climate, and the site TKPH if known
- 07Quantity, destination port and preferred Incoterm
Questions
Common questionsabout OTR tyre codes.
What does 23.5R25 mean on an OTR tyre?
23.5R25 is a wide base radial tyre with a nominal section width of 23.5 inches, made for a 25 inch rim. The same size in bias construction is written 23.5-25.
What is the difference between E3 and E4?
Both are rock treads for earthmover haulage tyres. E4 has a deep tread, typically about 1.5 times the E3 depth, which gives more wear life but runs hotter, so its TKPH rating is usually lower.
What does L5 mean on a loader tyre?
L5 is the TRA code for a loader and dozer tyre with an extra deep rock tread. L5S is the smooth version, used mainly underground and on sharp, abrasive rock, where cut resistance matters more than traction.
Is ply rating the number of plies?
No. Ply rating is a strength index for bias tyres, not a count of plies. Radial OTR tyres use stars instead.
Can a bias tyre be replaced by a radial tyre?
Often yes, in the same size and on a suitable rim, but bias and radial tyres should not be mixed on the same axle. Check the load, star rating and inflation with the machine and tyre makers before switching.
What is TKPH?
TKPH (tonne kilometre per hour) is the heat load capacity of a tyre. It is compared with the working TKPH of the site, calculated from mean tyre load and average working speed, to check that the tyre will not overheat.
Please note
Typical parameters only.
This guide explains parameters commonly used in international trade, for orientation. It is not a specification, an offer or a statement of available goods. Every deal sets its own specification in the written contract.
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