Sidewall cut on brand new tyre - permanent fix possible? I bought a new set of tyres (Continental Grand Prix 5000). Being an idiot, I managed to cut the sidewall of the tyre with a knife while removing the packaging. I have looked at repairing it, and came across items such as the Park Tool TB-2 Tyre Boot. However, I noticed that these fixes are only meant to be temporary, and not permanent. Is it safe and advisable to use a tyre boot to repair a new tyre which I plan to ride 3000-4000km on, or do I need to cut my losses and just buy a new one?

No, a tyre boot will absolutely not be enough. Some side cuts are repairable by stitching. However, it is better for MTB tyres that use smaller pressures. I do not know if it is likely to work on a road tyre.