The SportCrafters OverDrive Pro Rollers solve one of the biggest problems associated with rollers usually, they provide only so much resistance. But by combining the benefits of roller training with the resistance of a fluid trainer, the OverDrive Pro provides progressive resistance. This means that as the rollers spin faster, resistance increases in a non linear fashion, giving you all the benefits of balance and core strength development from traditional rollers with the added resistance found in stationary trainers. The OverDrive Pro Rollers were machined from aluminum. They feature 3. 25in drums with . 125in thick walls and are 15. 5in wide. The rollers were lathed on the axle for precision runout and balance. Also, they will not distort in the heat or sunlight because they are dynamically spin balanced. All SportCrafters rollers come with bearings that are greased and sealed, so there's no need to worry about maintenance. The OverDrive also features a steel frame that is zinc plated and powder coated to last and last. The Rollers are designed to fit wheel sizes 600 to 700c and 26 to 29in. It will accommodate wheelbases from 37. 5 to 44in, as drilled. There is no rider weight limit. The rollers' unfolded dimensions are 60 x 20 x 4. 25in, and folded it is 31. 5 x 20 x 5. 25in.