so what springs have more flex ST or Explorer?

 

I really dont think one is gonna flex more than the other. If it does its not enough to worry about. There are other limiting factors that effect your ability to flex to the max, like bump stops and shock length. So flexing shouldnt be your motive to get one or the other. Upgrading to ST or EX springs really depends on how much lift you want, what kind of ride quality your looking for and how much load you plan on running with.

 

explorer leafs 2-3 inches of lift

Sport track leafs 3-4 inches of lift


is that right?

 

If you keep your factory lift blocks in and you dont keep alot of stuff in the back of your truck, im pretty sure you could get a 4" lift from the ST springs.

 

sweet dude now the challenge of finding St leaves

 

For what it's worth, I was sitting here thinking about when I installed the longer shackles on the sport trac. I put the frame on stands, lowered the rear axle until it hung by the shocks and unbolted the factory shackles. When I installed the longer shackles I had to hand down on the spring and pry the shackles in. What I'm getting at is there would definitely be a fair amount of extra suspension droop there with longer shocks.
Sort of random but I was just thinking about it...

 

But with more travel you have to account for other things too. Brake lines, driveshaft length are just a few things that come to mind quickly. But if longer shocks are all that are "needed" then that's a cheap and easy mod to swap in ST or Explorer leaf springs with longer shocks.

 

Don't quote me on this, i've read and know that the stock driveshaft is ok up to 16" of travel, and I measure my stock travel to be about 9" possible.
As for the brake lines, I'm pretty sure you can unbolt the line from one of the clips on the axle housing or frame or something which will give some slack.
For brakes, you can install and longer rear stainless line which is pretty cheap to give you a few extra inches of travel/droop.
Other than that, the longer springs or longer shackles or both will definitely give a nice amount of travel for fairly cheap, which is what I plan on doing here very shortly. My stock rear shocks are rusting apart and have 82k miles on them, so they need replaced anyway.