Schwinn Men&#39;s High Timber Mountain Bicycle, 18"/Medium, Black Schwinn mountain frame with Schwinn suspension fork for controlled riding on tough trails Shimano twist shifters with 21-speed rear derailleur for quick gear changes on the trail Front and rear alloy linear pull brakes provide secure stopping power All-terrain, wide knobby mountain tires sit on light and durable alloy wheels for added stability Schwinn alloy crank offers optimal gearing and less maintenance on your end