When I talked with MCP on the phone when I started building a new F-125 laydown kart, before I got my superkart, they readily admitted that the speed and weight of a laydown 125 shifter kart was pushing the capbility of what they had available. I did buy the biggest stuff they had, but never finished the kart so can’t say how the brakes worked. MCP did suggest that I consider brakes from a shifter kart or superkart. Off the top of my head for superkarts you are looking at PVP, Kelgate, Brembo and possibly others. If you go that route, I would recommend buying the complete system front and rear along with the master cylinders.