Lightest set-up would be rear vee.....although with a magura mount frame it'll easily be the magura against the disc. If you want exact weights stop being so lazy and research it on tarty Hope mono trial 160 against Magura Hs33 + clamps Edit: And as for pro's and con's, use the search..... Very briefly: Disc Pros: * Better modulation, * Better wet weather performance ( in general ) , * Fairly tucked away compared to magura crossover. * Better hold than most magura set-ups Cons: * Heavier * Shifts weight distribution towards rear of the bike * Far easier to get contaminated * Once contaminated far harder and more expensive to put right ( £13 for pads, IPA to clean rotor ) * Less bite than a magura set-up * Needs fairly precise setting up, not a very easy job with snail-cams on some frames * Generally more hassle to maintain * Harder to bleed So, in conclusion; I reckon disc on the rear for a natural ( read competition ) mod bike. In all other cases, unless you very frequently require modulation ( think braunschweig ) then a magura is the easiest, cheapest, lightest and best performing option.