DFFT Tires and Wheels 1 — Questions and Answers
Question 1: A driver reports that the vehicle pulls to the left during braking. Which tire-related fault is most likely responsible?
- Uneven tire pressure between the front tires (Correct answer)
- Rear tires with insufficient tread depth
- Mismatched tire brands on the rear axle
- Overinflated spare tire
Correct answer: Uneven tire pressure between the front tires
Uneven tire pressure between the front tires causes one side to have more contact patch than the other, creating a pulling force during braking.
Question 2: What does a feathered or sawtooth wear pattern across the tread blocks of a tire typically indicate?
- Toe misalignment (Correct answer)
- Incorrect tire pressure
- Worn wheel bearings
- Brake caliper drag
Correct answer: Toe misalignment
Feathered or sawtooth tread wear is a classic sign of toe misalignment, where the tires are angled inward (toe-in) or outward (toe-out) excessively.
Question 3: A technician finds cupping (scalloped) wear around the circumference of a rear tire. What is the most probable cause?
- Worn or damaged shock absorbers (Correct answer)
- Excessive toe-out on the rear axle
- Overinflation of the tire
- Bent wheel rim
Correct answer: Worn or damaged shock absorbers
Cupping or scalloped wear is caused by worn shock absorbers that allow the tire to bounce and lose contact with the road, producing uneven wear patches.
Question 4: Which symptom would most likely indicate that a tire is significantly underinflated?
- Wear concentrated on both outer edges of the tread (Correct answer)
- Wear concentrated in the center of the tread
- Even wear across the full tread width
- Feathered edges on the tread blocks
Correct answer: Wear concentrated on both outer edges of the tread
Underinflated tires flex excessively, causing the outer edges of the tread to bear more load than the center, producing wear on both shoulders.
Question 5: A driver complains of severe vibration felt through the steering wheel at highway speeds. The vibration disappears at low speeds. What is the most likely tire or wheel fault?
- Wheel imbalance (Correct answer)
- Tire sidewall bulge
- Incorrect tire size
- Low tire pressure
Correct answer: Wheel imbalance
Wheel imbalance causes a speed-dependent vibration that increases with vehicle speed because the out-of-balance mass creates a centrifugal force proportional to the square of rotational speed.
Question 6: During a tire inspection, a technician notices a bulge on the sidewall of a front tire. What action should be taken?
- Replace the tire immediately as it is structurally compromised (Correct answer)
- Reduce tire pressure to relieve sidewall stress
- Monitor the bulge and re-inspect at the next service
- Rotate the tire to the rear axle to reduce load
Correct answer: Replace the tire immediately as it is structurally compromised
A sidewall bulge indicates internal structural damage to the tire's carcass, which can lead to sudden blowout and must be replaced immediately.
Question 7: What is the minimum legal tread depth for passenger car tires in the United States?
- 2/32 inch (Correct answer)
- 4/32 inch
- 1/32 inch
- 3/32 inch
Correct answer: 2/32 inch
The minimum legal tread depth for passenger car tires in the US is 2/32 of an inch, as measured in the principal grooves.
DFFT Tires and Wheels 1
A driver reports that the vehicle pulls to the left during braking.
Which tire-related fault is most likely responsible?