I have them on a 8 foot door. They stretch out to 71 inches with the door closed seem to work just fine. I do have a safety cable passing through the springs.
After calling my regular garage door co, and finding out they wanted to charge $125 for install of new part, I decided to search online. Found the exact part with ease for only $8 at Preferred Doors. Part arrived quickly and I installed it my self. Extremely satisfied!
After having a LiftMaster door opener installed in my new garage/shop, I soon realized that the HomeLink system in our '02 TrailBlazer would not synchronize with the new opener. I researched the pairing issue relating to my new door opener and discovered that I needed to install a bridge (repeater) to update to the current wireless control signal encoding. I ordered it, installed it, paired it, and it works as advertised. Fast ship, great price, and easy install -- pretty much Plug & Play!