These Swift 10" and longer springs are barrel design; the design is to solve all spring Deflection (bowing) problems. With bowing springs, you can expect spring rate inconsistency, and rubbing against shock body that would lead to damage on the shock adjusting perch thread.
One approach to assess spring deflection would be to increase the number of coils on the springs. With more coils on the spring, you will experience less bowing motion. This is the easy and cheaper method to solve the issue. But the downside of this method is a decrease in spring stroke, increase in un-sprung mass, and will affect the overall movement of other suspension components.
Unlike others, Swift designed barrel springs with ease and consistency of vehicle setup in mind, our barrel springs design have a maximum of 4" outer diameter (except B5 and B3 series)(Usually located on the center coil of the spring). Because most other manufacture do not design their barrel springs with this rule, most of their barrel springs outside diameter will differ from one rate to another. This creates a hard time for racers especially with tight clearances to test and see which rates will fit and which rate does not. A heavier rate spring can interfere with the suspension A-arm or other suspension components.
These springs are designated by (Free Height)-(Inner Diameter)-(Rate)
140 = 14" Free Height
250 = 2.5" Inner Diameter
300 = Rate in Lbs/in