Module 03: Tires and Brakes¶

← Module 02: Fluids and Filters | Topic Home | Next → Module 04: Battery and Electrical

Tires are your only contact with the road; brakes are your ability to stop. Learn to inspect, maintain, and understand both systems before any safety-critical situation arises.

Table of Contents¶

1. Overview
2. Prerequisites
3. Objectives
4. Theory
5. Key Concepts
6. Examples
7. Common Pitfalls
8. Cross-Links
9. Summary

Overview¶

[!NOTE] This module is a stub. The full theory, examples, exercises, test, and answer key are planned for a future expansion.

Tires are the only part of your car in contact with the road — a contact patch roughly the size of your hand on each corner. Everything the car does (accelerate, steer, stop) depends on those four patches maintaining grip. Brakes convert the car's kinetic energy into heat through friction. Understanding both systems lets you recognize problems before they cause accidents, and perform the most common service tasks yourself.

Difficulty: Beginner  |  Estimated time: 4 hours

Prerequisites¶

• [[cars-maintenance/modules/01_introduction]] — vehicle systems overview and safety procedures
• [[cars-maintenance/modules/02_fluids-and-filters]] — brake fluid knowledge (hydraulic system context)

Objectives¶

By the end of this module, you will be able to:

1. Decode a tire size specification (e.g., 205/55R16 91H) — width, aspect ratio, diameter, load index, speed rating
2. Check tread depth accurately and identify wear patterns that indicate alignment, pressure, or suspension problems
3. Rotate tires correctly for front-wheel drive, rear-wheel drive, and all-wheel drive vehicles
4. Inspect brake pads for remaining friction material thickness without removing the wheel
5. Diagnose brake symptoms: squealing, grinding, pulsation, and pulling — and know what each indicates
6. Explain the difference between brake pad replacement vs. rotor replacement criteria
7. Describe the hydraulic disc brake system: how pedal force becomes clamping force at the caliper

Theory¶

Tire Anatomy and Specifications¶

Radial tire construction: belts, plies, bead, tread compound, sidewall. Reading the tire sidewall: size code, DOT date code (manufacturing week/year), treadwear/traction/temperature ratings. When to replace based on tread depth (2/32" legal minimum, 4/32" recommended safety minimum), age (6–10 years regardless of tread), and damage criteria (sidewall bulges, cord damage, punctures near sidewall).

Tire Pressure and TPMS¶

Why correct pressure matters: fuel economy, tire wear patterns, handling, and blowout risk. How TPMS works (direct pressure sensor vs. indirect via ABS wheel speed comparison). Pressure vs. temperature relationship (1 PSI per 10°F). Why you measure cold pressure (before driving or after sitting 3+ hours).

Tire Rotation Patterns¶

Front-wheel drive: X-pattern or forward-cross. Rear-wheel drive: rearward cross or X. All-wheel drive: X-pattern. Why directional tires can only be rotated front-to-rear on the same side. Staggered fitment (different front/rear sizes) and why some vehicles cannot rotate tires.

Disc Brake System Mechanics¶

Master cylinder → brake lines → caliper → pads → rotor. How hydraulic pressure creates clamping force. Brake fade: what it is, what causes it (overheated fluid, glazed pads, warped rotors), how to avoid it. Disc vs. drum brakes: why discs dominate modern vehicles (heat dissipation, self-cleaning, consistent pedal feel).

Brake Pad Inspection and Replacement Criteria¶

Minimum pad thickness: 3 mm (⅛ inch) of friction material. Wear indicators (squealing strips) and what that sound means. How to inspect through the wheel spokes. Rotor thickness measurement and minimum specification. Rotor resurfacing vs. replacement decision.

Reading Brake Symptoms¶

Key Concepts¶

• Tread wear indicators: Raised rubber bars at 2/32" tread depth molded into tire grooves — visible when tires need replacement
• Brake fade: Temporary loss of braking effectiveness due to heat; happens during prolonged heavy braking (descending a mountain, racing)
• Rotor minimum thickness: Manufacturer-specified minimum safe rotor thickness stamped on the rotor hat; below this, rotors cannot safely absorb heat
• Brake bias: Front brakes do approximately 70–80% of stopping work (weight transfers forward during braking); front pads wear faster
• DOT date code: Four-digit code on tire sidewall (WWYY) showing week and year of manufacture; tires older than 6–10 years should be replaced regardless of tread depth

Examples¶

To be fully written in the complete module expansion:

• Reading and decoding a full tire sidewall (size, date, ratings)
• Performing a brake inspection through the wheel spokes without removing wheels
• Diagnosing tire wear patterns: center wear (overinflated), edge wear (underinflated), one-sided wear (alignment), cupping/scalloping (worn suspension)

Common Pitfalls¶

• Checking tire pressure when hot (gets a reading 4–6 PSI too high)
• Using the tire's max pressure from the sidewall instead of the vehicle's recommended pressure from the door sticker
• Ignoring a squealing brake sound until it becomes grinding — the wear indicator is designed to give you advance warning; pay attention to it
• Forgetting to check spare tire pressure — spare tires typically lose pressure faster than mounted tires
• Resurfacing (turning) rotors that are already at or below minimum thickness — this removes material and makes them thinner and more prone to warping

Cross-Links¶

• [[cars-maintenance/modules/01_introduction]] — initial tire pressure check and warning light (TPMS) introduced in Module 01
• [[cars-maintenance/modules/06_suspension-and-steering]] — tire wear patterns often indicate suspension or alignment problems covered in Module 06
• [[cars-maintenance/modules/08_diy-repairs]] — brake pad replacement step-by-step procedure covered in Module 08
• [[cars-maintenance/modules/11_road-trips-and-emergencies]] — flat tire emergency procedure covered in Module 11
• [[cars-maintenance]] — CHEATSHEET.md tire size decoder and brake inspection thresholds table

Summary¶

• Tire size codes (width/aspect ratio/diameter/load/speed), DOT date, tread wear ratings
• Tread depth inspection (minimum 2/32", recommended 4/32"), wear pattern diagnosis, rotation patterns
• Disc brake hydraulics: pedal force → hydraulic pressure → caliper clamping → friction → deceleration
• Brake inspection: pad thickness (minimum 3mm), rotor condition, symptom interpretation (squeal vs. grind vs. pulsation)
• Pressure checks must be done cold; use door-sticker spec not tire-sidewall max