<div class="htmlview paragraph">Typical solutions for automotive strength problems are complicated by such variables as driver habits and road conditions, but the inclusion of a safety factor when designing for fatigue loading modifies these intangibles to some extent. Two different loading systems are discussed in this article to demonstrate the application of formulas for measuring magnitudes of loads and for estimating frequencies of fatigue failure in road test experience, service mileage, information, and strength comparisons. The author emphasizes that such statistical calculations, used in place of former rule-of-thumb methods, produce more realistic safety factor values and also provide a faster and more economical approach toward achieving long life and reliability of parts.</div>