A drive chain riding at the top of the teeth on a sprocket is caused by?

When a drive chain is riding at the top of the teeth on a sprocket, it usually indicates that the sprocket teeth are worn out. Worn teeth can lose their shape and contour, impacting how the chain engages with them. As the teeth degrade, they can no longer properly support the chain, which leads to the chain sitting higher than intended on the sprocket. This misalignment can cause increased chain wear and can also lead to premature failure of the sprocket and chain itself.

While issues like slackness or tightness could affect the performance of a chain drive system, they typically do not cause the chain to ride specifically at the top of the teeth. Similarly, using a chain with the wrong pitch for the sprocket can lead to other alignment and fitment issues but would not specifically result in the chain riding on top of the teeth as a direct indication of wear. Thus, the key reason behind the chain riding at the top of the teeth in this scenario is the wear and degradation of sprocket teeth.