On Which Pulley Does Belt Slippage Occur First?
4 Answers
Belt slippage first occurs on the smaller pulley. Introduction to the Contact Arc: The contact arc can be divided into two parts: the part with relative sliding (sliding arc) and the part without relative sliding (static arc). The central angles corresponding to these two arcs are called the sliding angle and the static angle, respectively. The static arc is always located at the beginning part where the belt wraps around the driving and driven pulleys, while the sliding arc is located on the part of the contact arc where the belt leaves the driving and driven pulleys. When the belt is not transmitting load, the sliding angle is zero. Elastic Sliding: Elastic sliding only occurs on the sliding arc of the belt. As the load increases, the sliding angle gradually increases, while the static angle gradually decreases. When the sliding angle increases to the wrap angle of the pulley, the limit state is reached, and the effective tension of the belt drive reaches its maximum (critical) value. If the working load continues to increase, significant relative sliding between the belt and the pulley will occur, resulting in slippage. Since the wrap angle on the larger pulley is always greater than that on the smaller pulley, slippage always occurs first on the smaller pulley.
I remember when I had a belt drive slipping issue while driving before. The belt is that kind of strap connecting the engine to components. Slipping usually starts from the smaller pulley end, like the drive pulley on the engine side, because it's smaller and has less grip than the larger pulley. That time, my car made a squealing noise when driving and lacked power during acceleration. After checking, I found the belt was slipping first at the drive pulley, probably because the belt was loose or the pulley surface was worn. I rushed to get it fixed, and the mechanic said the wrap angle was too small, causing insufficient friction and easy slipping. He recommended checking belt tension during every maintenance to prevent severe slipping that could damage the engine. If the belt wears out completely, the entire drive system could fail, affecting the air conditioning compressor or water pump operation.
I've dealt with numerous belt slippage issues. My repair experience tells me that belt slippage always occurs first on the driving pulley, which is usually the small pulley driven by the engine. With its shorter circumference and less belt contact area, the small pulley is prone to slippage, especially when the belt is aged or the tensioner fails. The other day, a car came in with abnormal noise and insufficient power - upon inspection, it was the belt slipping on the driving pulley, accompanied by an oil leak. The solution was to check belt wear, adjust tension, and replace if necessary. Daily driving should include listening for changes in belt noise - early squeaking might be a warning sign. Keeping belts clean and free from oil contamination maintains friction and extends service life.
Belt slippage often occurs first on the smaller pulley, most commonly the engine drive pulley. This is a design characteristic: the smaller pulley has a shorter contact arc and weaker friction, causing the belt to slip under heavy load. I recommend regular maintenance, checking and adjusting belt tension as needed, and ensuring pulley surfaces are not overly smooth or contaminated with oil. Prevention is better than repair—routinely inspect belts for cracks or looseness, and address minor issues early to avoid major failures. Remember, safety comes first; severe belt slippage can lead to belt breakage or system failure, so always check before driving.
