Everything Andy says is plausible!PIGEON":3691azrl said:Magics are front and rear specific, front is skinnier. I could try it to definitly rule out the rim as the cause of the cuts, but the tyre dragging the inner tube about sounds so plausible and is also consistent with the shape and location of the cuts that i think it won't be necessary.
I know they are front and rear specific, but it might help you establish whether the Magics are incompatible with your rim, or whether there is a fault with the bead of that particular tyre.
The fact that you have a Schraeder-size hole which is cutting a Presta tube, even with the lock nut tight (presumably) makes me suspect that you need a rim with a Presta-size hole - a Presta tube locked onto a Presta-size hole might work, even if the Magics are moving slightly.
[I seem to recall you used to be able to buy adapters to convert Schraeder holes into Presta holes]
I would assume that the greater the pressure, the less tyre movement you should get. But if there is a fault with the bead, there may be no solution to the problem.