The original progressive rate fork springs soak up the small road bumps, yet are firm enough to absorb the molar-rattling ones. Spring rates have been chosen to reduce front end dive during braking, yet still provide excellent ride comfort. They warranty the fork springs for life. Progressive rate fork springs have several advantages over straight rate springs. A straight rate spring only offers linear resistance to compression and is a compromise. For example, if you have a 20lb straight rate spring, it will take 20lbs of force to compress the spring one inch. It will take 20 more lbs. of force to compress it the next inch, and so on, until the end of the travel. A Progressive Rate Spring has the advantage of a rising rate resistance to compression. For example, a 15lbs. - 25lbs. progressive rate spring will take 15lbs. to compress it the first inch, 17lbs. more the next inch, and so on, until the end of the travel, taking 25lbs more to compress it the last inch. The benefit of this is that the spring can be soft enough at the start of the travel to offer a plush ride, yet be firm enough at the end of the travel to soak up the big bumps. Measures 1.48 inch OD by 14.75 inch length.