98 Feet Zip Line Kit for Kids and Adult Up to lb with Zipline Spring Brake and Safety Harness, Zip line Trolley with Handle and Thickened Seat,for Backyard Playground Entertainment/5(). Zip line cables vary in length from 30 feet to feet. A longer cable generally means faster rides and an increase in height, as the lines bow in the middle. Longer cables are often thicker to support their own weight. And with the added length comes added speed and the need for a reliable braking system.