Motorcycles with engine displacement under ______ cc have a specific speed limit in Japan.

In Japan, motorcycles with an engine displacement of under 125 cc have specific speed limits that apply to them. This classification helps establish regulations based on the capabilities and power of the motorcycle. For smaller motorcycles, which generally fall into the category of light vehicles, these speed limits are designed to enhance safety for both the riders and other road users.

Motorcycles under this engine size are subject to lower speed limits compared to larger motorcycles, which reflects their performance limitations. Regulations like this are common in various countries to promote safer riding practices, especially for less powerful vehicles that may not handle high speeds as effectively.

The other displacement options of 100, 150, and 200 cc, while they do pertain to motorcycle categorization, do not correspond to the specific speed limit regulations outlined in Japanese traffic laws for the smallest motorcycle class. Therefore, the correct displacement marking for this particular speed limit regulation is indeed 125 cc.