As with anything, there can be such a thing as pedals that are too big for a mountain bike. It really depends on the size of the bike and the rider. Some people might feel more comfortable with smaller pedals while others might prefer larger ones. There isn't necessarily a right or wrong answer when it comes to pedal size, but it's something to consider when choosing pedals for your mountain bike. If you're not sure what size pedal you need, it's always best to consult with an experienced bicycle mechanic who can help you select the best option for your bike and riding style.