---
title: "Tyre construction, types and factors affecting life"
subject: "Automotive Technology"
chapter: 8
key: "semester_5/automotive_technology:tyre-construction-bias-radial-life"
source: https://www.bctengineer.com/q/semester_5/automotive_technology/tyre-construction-bias-radial-life
site: BCT Engineering
---

# Tyre construction, types and factors affecting life

Automotive Technology · Chapter 8: Wheels and Tires

- Asked in: year not given, 6 marks
- Video: [Tyres and Tyre ply Types](https://www.youtube.com/watch?v=8HvGy07KpVQ) — parag Mangave
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/automotive_technology/tyre-construction-bias-radial-life
- Whole chapter: https://www.bctengineer.com/md/semester_5/automotive_technology/chapter-8

## Question

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.

## 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.

## Answer

#### Construction of a tubeless radial tyre

```text
 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the role of the inner liner in a tubeless tyre?
   A. It is an air-tight butyl layer that replaces the tube
   B. It locks the tyre to the rim
   C. It stiffens the tread
   D. It carries the markings
   Answer: A. In a tubeless tyre the butyl inner liner holds the air, and the bead seats on the rim. (Key point: Inner liner)

2. Which is true of radial-ply compared with bias-ply tyres?
   A. Higher heat build-up and shorter life
   B. Cords at 30 to 40 degrees, stiff sidewall
   C. Cords at 90 degrees to the bead with belts, flexible sidewall, lower heat and rolling resistance
   D. Cheaper and better grip
   Answer: C. Radials have radial cords plus belts, so lower heat, lower rolling resistance, 30 to 50 % longer life and better grip, but they cost more. (Key point: Radial vs bias)

3. What is the effect of under-inflation?
   A. No change to wear
   B. Wear on both shoulders, more rolling resistance, heat and possible failure
   C. Centre wear and a harsh ride
   D. Better fuel economy
   Answer: B. A soft tyre sags so the shoulders carry the load, giving shoulder wear and heat. (Key point: Under-inflation)

4. What is the effect of over-inflation?
   A. Heat build-up and failure
   B. Wear on both shoulders
   C. Wear in the centre of the tread, harsh ride, reduced grip and more risk of impact damage
   D. Lower rolling resistance with longer life in every case
   Answer: C. An over-hard tyre bulges so the centre contacts the road and wears faster. (Key point: Over-inflation)

## Related in Automotive Technology

- [Phases of combustion in a CI engine](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Acombustion-ci-engine-phases) — Automotive Technology, chapter 3
- [Knock and pre-ignition in SI engines](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Aknock-and-pre-ignition-si-engine) — Automotive Technology, chapter 3
- [Disc brakes and drum brakes](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Adisc-brake-vs-drum-brake) — Automotive Technology, chapter 7

## Related in other subjects

- [Shock effects and factors affecting damage](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Ashock-physiological-damage-factors) — High Voltage Engineering, chapter 2
- [Inflation, effects, inflation-free rate](https://www.bctengineer.com/question.md?key=semester_6%2Fengineering_economics%3Adefine-inflation-effects-implied-rate) — Engineering Economics, chapter 8
- [Cost vs value; factors affecting valuation](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Acost-vs-value-factors) — Construction Management, chapter 13
- [Bias and offset currents: effects and reduction](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Abias-offset-currents-effects) — Advanced Electronics, chapter 2