hello i bought a Triban RC 120 with disk brakes and the brakes arent adequate for me, instaling hydraulic brakes isn't an option because that requires changing the whole group set so the next best thing is a mehanical brake, or an cable actuated hydraulic caliper, which model is the best that is currently available
That's a good question.
Decathlon's Triban RC 120 DISC is a reasonably priced road bicycle with some compromises - such as the underwhelming brakes.
Even if budget allowed for changing the whole groupset, I would still try to stick with mechanical disc brakes for the ease of maintenance (swapping a brake cable is a lot faster than bleeding hydraulic brakes, especially the road bike models).
Factory discs are 160 mm in diameter (unless the website specs are wrong). Replacing them with 180 mm diameter discs might put some stress on the fork (
disc brake fork stress explained) - I would not advise that.
Swapping the discs ("rotors") for some higher quality 160 mm ones wouldn't hurt, but I would first try some good quality brake calipers.
Avid BB7 Road mechanical disc brake calipers are great (link to the bike24 online store). They are durable and perform very well.
Note:
MTB mechanical disc brake calipers won't work well with road brake levers (STI-s). The above-mentioned calipers (Avid BB7
R) are designed for road ("drop bar") brake levers.
The model I linked to comes with 160 mm discs and some mounting adapters - I couldn't find calipers sold separately, but later one, you could buy just new discs when the old ones wear.
You will need compatible pads. These are "semi-metallic" - so they perform OK when cold, but also OK when hot, and aren't as aggressive on the discs as the "fully metallic" pads:
https://www.bike24.com/p2214590.html
I haven't tried them personally, but I can't find other semi-metallic models available right now (doesn't mean there aren't any). Based on the pictures and description, they should work with Avid BB7 calipers.
Having said that, even decent organic pads should work OK, and you could give those a try first with the new calipers, and if you aren't happy with the performance, you could use the organic pads for the rear brake, and put semi-metallic on the front.
Speaking of front and rear, you could also buy just the front caliper in decent quality, as the front brake is what matters most - Avid BB7 aren't cheap.
Hope this helps.
Relja