Please tell me when to replace rubbers.

The lifespan of a rubber depends on many factors, such as play time or intensity of training. The more you practice, the faster the rubber can wear out. When not in use for a longer period, a rubber can also lose elasticity.
We recommend replacing a rubber regularly depending on usage time.

Pimples-in rubber:
When the surface loses its grip, or when the surface is losing the sheen and becomes whitish.

Pimples-out rubber:
When pimples start to break, or when the surface is discolored, and the bounce and rotation become smaller.