upper tracks to sag?

I had to scratch build a roller bearing to get a sag on this 1/35 RC. Works pretty well without drag. I have since altered the skirt so it's hidden some more.

I use either the thread or the pins, if the tank has a lot of open space between the upper run of track and the fenders, like a Tiger, I go with thread. If the fenders are close the the upper run of track, like a KV I, I use the pins, obviously because the fenders help hide the pins. Both methods are easy and work very well.

Whoah, A hairdryer, I' would nver have thought of that does it actually work or does your model just melt?

In addition to Rob's techinque a harder yet alternate way to do it is to but pins over the tops of the tracks and insret them in the Hull of the tank its supposed to work but
I've never tried it

Not a bad idea at all Rob for the vinyl tracks. I've heard of using hairdryers and various other methods to try and induce sag but have never attempted them myself. I've carefully stretched them in the right areas to produce a little sag but nothing quite compares with using indy links in that department I'm afraid.

nice idea Rob, will get some thread before next build

It depends. No problem using individual links but with vinyl links, I use a couple of different methods. First I try to do what you do by gluing the top down to a few road wheels. If that won't work for various reasons, I use transparent thread (used to hem trousers) to tie them down. I bought a spool of the darker colored transparent thread and it has lasted for years.

Just loop the thread between the pair road wheels and thread it through some of the natural cracks in the track (or use a needle to poke it through). Works pretty good.