- Practice · 6 marks
Tyre construction, types and factors affecting life
Short answer
A tubeless radial tyre has plies at 90° to the bead, steel belts under the tread, and an inner liner for air retention. Bias-ply tyres use crossed plies at 30–40°, resulting in stiffer sidewalls, higher heat build‑up, and shorter tread life. Tyre life depends on inflation, load, alignment, and driving habits; under‑inflation wears shoulders, over‑inflation wears the centre.
Describe the construction of a tubeless radial tyre. Differentiate between bias-ply and radial-ply tyres. List the factors that affect tyre life and the effects of incorrect inflation pressure.
Construction of a tubeless radial tyre
Tread ----------- (grooves)
Belts (steel) -- under tread
Carcass plies (radial cords, 90 deg to bead)
Inner liner (air-tight, replaces tube)
Sidewall Bead (steel wire) seats on rim
- Tread: thick rubber with a pattern for grip and drainage; the part that wears.
- Belts: 2 steel (or fabric) layers under the tread, which stiffen it.
- Carcass (body plies): polyester or steel cords that give strength and hold the air pressure.
- Inner liner: butyl rubber, air-tight layer in a tubeless tyre.
- Sidewall: protects the carcass and displays markings.
- Bead: high-strength steel wire bundle that locks the tyre to the rim.
Bias-ply vs radial-ply
| Point | Bias-ply | Radial-ply |
|---|---|---|
| Cord angle | 30 to 40 degrees, crossed | 90 degrees to the bead, with belts |
| Sidewall | Stiff | Flexible |
| Heat build-up | High | Low |
| Tread life | Shorter | 30 to 50 % longer |
| Rolling resistance and fuel use | Higher | Lower |
| Handling and grip | Poorer | Better |
| Cost | Cheaper | Dearer |
Factors affecting tyre life
- Inflation pressure, vehicle overloading and speed.
- Wheel alignment (toe, camber) and balance, suspension condition.
- Driving habits: sharp braking, cornering, fast starts.
- Road condition and temperature; tyre rotation and storage.
Effects of incorrect inflation
- Under-inflation: wear on both shoulders, higher rolling resistance, heat and possible failure, poor steering.
- Over-inflation: wear in the centre, harsh ride, reduced grip and more risk of impact damage.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Phases of combustion in a CI engine · Automotive Technology, chapter 3
- Knock and pre-ignition in SI engines · Automotive Technology, chapter 3
- Disc brakes and drum brakes · Automotive Technology, chapter 7
- Shock effects and factors affecting damage · High Voltage Engineering, chapter 2
- Inflation, effects, inflation-free rate · Engineering Economics, chapter 8
- Cost vs value; factors affecting valuation · Construction Management, chapter 13
- Bias and offset currents: effects and reduction · Advanced Electronics, chapter 2