Shimano BR-IM31 is an Inter-M brake system designed to provide reliable and efficient braking performance for bicycles. It features a unique design with a brake drum filled with grease, resulting in a slightly heavier wheel turning compared to conventional brakes, especially in cold conditions. The Inter-M brake is not suitable for mountain bikes due to potential overheating of internal parts during hard braking. It's essential to use Shimano brake cables and levers as a set to ensure optimal performance. The inner cable movement should be at least 14.