I have a beautiful street bike and I thought of using it in the south on the street and in Bangkok on a tracx trainer.

Today I needed half a day to pack it safe and I am still not confident if it is really safe.

So my idea is, buy a bike only for the trainer. So it doesn't matter how heavy, it doesn't need brakes, it need only basic gear. Back wheel 5 front 2. Of course it could be 20 years old. Just the bearings should be OK and the size of the bike.

Any idea/experience on that?

I do the same, but it should be aluminum framed, not steel. You can search online, but steel has a habit of deforming under the forces a trainer puts in it, for all but the most expensive types of tubing (Reynolds/Columbus). Your cheap Hi-Ten steel frame in Thailand probably won't last long.

I do the same, but it should be aluminum framed, not steel. You can search online, but steel has a habit of deforming under the forces a trainer puts in it, for all but the most expensive types of tubing (Reynolds/Columbus). Your cheap Hi-Ten steel frame in Thailand probably won't last long.

I don't understand that. The trainer locks on the back wheel and put surely less force than the street would do. What do I miss?

It's because it's clamped at the rear dropouts, on the road the forces are different as the contact patch is through the wheel only and the frame is free to move around, on the trainer it isn't. You'll even find some bike manufacturers will not warranty the frame if you've used it on a trainer.