Automotive Certification Practice Exam 2026 – Complete Prep Guide

The correct response highlights how changes in tire dimensions can directly affect speedometer accuracy. When taller tires are installed on a vehicle, they change the overall circumference and the distance the vehicle covers per tire revolution. The speedometer is calibrated based on the original tire specifications. Therefore, if taller tires are used, the speedometer will reflect a greater speed than the actual speed because it is measuring based on the incorrect circumference associated with the original tire size.

This discrepancy can cause fluctuations or inaccuracies in the speed reading as the vehicle moves. Taller tires lead to the vehicle traveling a further distance for each rotation, which can confuse the speedometer and result in erratic readings.

Understanding this relationship allows vehicle owners and technicians to recognize that modifications to tire size can lead to speedometer issues, ensuring proper adjustments or recalibrations are made to maintain accuracy and reliability in readings.