What is the Synchronous Adhesion Coefficient?
2 Answers
The ground adhesion coefficient when both front and rear wheels lock simultaneously is referred to as the synchronous adhesion coefficient. The synchronous adhesion coefficient φ0 is calculated as (Lβ-b)/hg. Generally, an empty-load synchronous adhesion coefficient of 0.5~0.6 is considered appropriate, while a full-load synchronous adhesion coefficient of 0.8~0.9 is more suitable. Additional information: Importance of selecting the synchronous adhesion coefficient: 1. The synchronous adhesion coefficient has a significant impact on the directional stability of a vehicle during braking. 2. Once the total mass and the center of gravity position of the vehicle are determined, the I curve can be plotted. The β line is determined by the distribution of braking force between the front and rear axles. 3. During design, the β value can be adjusted to achieve an appropriate match between the β line and the I curve, ensuring a suitable synchronous adhesion coefficient. 4. The larger the β value, the smaller the slope of the β line, and consequently, the larger the synchronous adhesion coefficient φ0.
As an average car owner, I didn’t know what synchronous adhesion coefficient was until an engineer friend explained it to me. Simply put, it’s an ideal parameter for the braking system—the point where the grip between the front and rear tires and the road reaches perfect balance when you slam on the brakes. This coefficient determines whether the vehicle will fishtail or nose-dive during hard braking, with higher values indicating more stable braking performance. I specifically checked for my SUV, and most urban SUVs have coefficients between 0.7-0.9, while off-road vehicles usually have higher values. If a car isn’t properly maintained—like having severely worn tires—the actual adhesion coefficient drops, leading to noticeably longer braking distances at high speeds, something I’ve deeply experienced during rainy highway drives.
