The 500 Series Kit was introduced as a result of many customers requesting a kit that provides more hill climbing power for the steepest of hills and torque to move heavier loads. The 500 Series Kit is perfect for heavier riders, fat bikes, trikes, tandems, and more! Each kit is hand built in the USA customized for each order! If you need help determining what sizes and options you need please give us a call at (866)933-8716! At Leeds, we pride ourselves on our expertise and customer service.