Best suited for the Gboost-System are tires with a flat even running surface in the center. Typical mountain bike tires are not recommended since they generate vibrations and noise. We recommend switching to tire types as shown on the left side of the picture below.
By the way, you should be aware that mountain bike tires have a higher roll resistance than street or city tires. So you will need to put more energy into your bike to reach the same distance with a mountain bike tire than with a city tire, or in other words, your pedelec runs less far on the same batterie.