How do OTR tyres differ from truck tyres?
The core differences are the rubber compound and the tread depth. OTR tyres use a cut- and tear-resistant compound, a markedly deeper tread to withstand mechanical abrasion from crushed rock, and a thicker casing to resist punctures. In return, operating speed is limited and the tyre is considerably heavier than a truck tyre of the same diameter.
Short answer: OTR tyres are selected by machine type and wheel load, not by kilometres. Mining dump trucks and wheel loaders generally use radial; rollers and port container handlers generally use bias.
Radial or bias for each machine type?
| Machine type | Suitable construction | Reason |
|---|---|---|
| Rigid dump truck | Radial | Covers long distances in the mine; requires low heat generation and low rolling resistance |
| Wheel loader | Radial | Continuous dig-and-reverse cycles; requires a wide contact patch and cut resistance |
| Mobile crane | Radial | Heavy loads; stability during lifting is required |
| Pneumatic-tyred roller / compactor | Bias | Smooth tread, resistant to asphalt heat, low speed |
| Port container handler | Bias | Withstands momentary overload and repeated impact |
| Motor grader | Radial or bias | Depends on load and haul route |
What do the star markings on OTR tyres mean?
OTR tyres do not use a ply rating (PR) but star markings to denote load class: one star, two stars and three stars correspond to progressively higher load levels. In this range the load class is given separately in the load class field and is not merged into the tyre size.
- One star (*): basic load class, for small machines or short hauls.
- Two stars (**): medium load class, common on dump trucks and mid-size wheel loaders.
- Three stars (***): highest load class, for large mining dump trucks and mobile cranes.
Selecting tyres by machine type: the steps
- Establish the machine type and wheel load: divide the axle load by the number of wheels; do not use the machine's nominal payload.
- Establish the operating conditions: sharp rock quarry, mud, sand or port concrete — each condition calls for a different compound and tread.
- Choose the construction: radial for long hauls and heavy loads, bias for impact and low speed.
- Check the load class: the star rating or ply rating must be sufficient for the actual wheel load.
- Check the outside diameter: it affects ground clearance and the machine's drive ratio.
OTR tyre sizes in the range
The current range covers 34 radial OTR sizes and 43 bias OTR sizes, from 15-inch to 49-inch rim sizes. The table below summarises them for quick reference.
| Rim | Sizes in the catalogue | Typical vehicles |
|---|---|---|
| Rims 15–16 inch | 6.50R16, 7.00R15, 7.00R16, 7.50R16, 8.25R16 | Light trucks and small coaches |
| Rims 17.5–19.5 inch | 9.5R17.5, 215/75R17.5, 245/70R17.5, 245/70R19.5, 265/70R19.5, 285/70R19.5 | Medium trucks and buses |
| Rims 20–21 inch | 8.25R20, 9.00R20, 10.00R20, 11.00R20, 12.00R20, 14.00R20, 16.00R20, 365/80R20, 365/85R20, 425/85R21 | Heavy trucks and long-distance coaches |
| Rims 22.5–24 inch | 9R22.5, 10R22.5, 11R22.5, 12.00R24, 12R22.5, 255/70R22.5, 275/70R22.5, 275/80R22.5, 295/60R22.5, 295/75R22.5, 295/80R22.5, 315/80R22.5, 325/95R24, 385/65R22.5, 425/65R22.5, 445/65R22.5 | Tractor units, heavy trucks and trailers |
Construction tyre maintenance
- Check pressure every shift — OTR tyres run under-inflated fail very quickly and cannot be restored.
- Inspect sidewall cuts and punctures after every shift at the quarry.
- Clean dirt and rock off the rim to prevent corrosion and air leakage.
- Record operating hours to plan replacement instead of waiting for the tyre to fail.
Frequently asked questions
- Can OTR tyres be used on highway trucks?
- No. OTR tyres have a low speed limit and are not designed for continuous operation on asphalt.
- How does the star rating differ from ply rating (PR)?
- The star marks are the load rating for OTR tyres; PR is the ply rating for tyres with a ply carcass. The two systems do not convert directly into each other.
- For mining, should I choose radial or bias?
- Mining dump trucks and wheel loaders usually run radial; rollers and port container handlers usually run bias because they need impact resistance.
- How often must construction tyres be replaced?
- By operating hours and actual condition: tread below the limit, cracked sidewall, or deformed casing.
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