That would kind of depend on :-
The angle of the incline
The weight of the load you intend to haul.
Ordinary 'dressmaking' thread tends to be a bit 'hairy', and if running on rollers in the track can generate static electricity and attract fluff. Fishing line could be just as bad for static. If there is a chandler/sailmaker, saddlery, or leathercraft shop near you, take a look at the heavy threads they use.... they may even be waxed, which would cut down the 'hairiness', but might attract more fluff.
If you're modelling in a large scale, you could try bicycle brake or gear cable!
Have fuN (with a capital N)
My Mum calls me Steve.
1:32 on 16·5mm track. Gnot strictly minimum gauge... but it is the minimum that I'm working with !
And now... a critter in 1/24th... from scratch!