tracks that sag

There's a couple of different ways that you can use to make tracks sag. The first and most expensive is to go buy a set of metal tracks, they sag without any extra work. The second method that I know of is to tie the tracks done. For instance on a Panther where there are no return rollers you can thread a piece of string into the track and pull it down until it looks good then tie the string between the road wheels (no one will even see the string unless they really look hard). The third and final method that I've used is on a kit that does have return rollers. For this example think Panzer IV. What I have done with these is to locate where the top of the track needs to be between each roller. Drill a small hole into the hull side at this point and insert a piece of road (a straight pin will work too). Place the track underneath the rod when placing it on the hull and voila...track sag.
Hope this helps.

I've used the pin-in-the-hull method and it works great, just paint the pin black to make it unnoticable. I've also used individual link tracks to great sucess.

Well I pretty much kissed the vinyl tracks good bye a long time ago. I only use either Model Kasten Workable individual linked tracks (plastic) or Fruil Model (white metal). The sag is very realistic, and easy to work with.