All trampolines springs have what is called a "Resting Stretch" and an "Active Stretch." The Resting Stretch is defined as the amount of stretch on the spring when it is attached to the trampoline frame and bed and nobody is jumping on it -- it is "at rest." The Active Stretch is defined as the length to which the spring could stretch when an average size person is "actively" jumping. See the chart below:
- 9 Inch Spring -- Resting Stretch of 11 - 12 in. -- Active Stretch of 14 - 15 in.
- 10 Inch Aussie "Jumbo" Spring -- Resting Stretch of 14 - 15 in. -- Active Stretch of 18 - 20 in.
- 10 1/4 Inch Aussie High Performance Spring -- Resting Stretch of 15 - 16 in. -- Active Stretch of 19 - 21 in.
As you can see, there is quite a difference. You will also note that depending on what spring size you choose has an impact on the actual size of the trampoline bed needed to correctly fit your trampoline frame. HAPPY JUMPING!!