The Water Sports Industry Association (WSIA) recommends using products marketed as tube ropes, as they are stronger than a standard water ski rope and can thus reliably tow multiple riders. Look for tow ropes that align with the max weight capacity of your tube, so you can handle all riding scenarios. By WSIA standards, a 60-foot rope is an ideal length. Rope tensile strength ranges from 1,500 pounds to over 4,100 pounds; use the max weight allowance of your tube to find the right rope.