The Mouse and the Motorcycle, by Beverly Cleary, 1965.

Keith is a guest at the Mountainview Hotel, and Ralph is a permanent occupant, but their love of motorcycles (and the magic of sound effects) forges a friendship between the two adventure-loving boys, even if Keith is a human and Ralph is a mouse. Loyalty, bravery, generosity, and high adventure all are possible three inches above the floor. Suitable for elementary ages. Recommended.