The first radial tyres fitted to the Mini were the 145 x 10 Dunlop SP41. Prior to that, a cross-ply 5-20 x 10 was fitted, usually a Dunlop.
The SP41 was a good tyre. I recall my first new car, a 1964 Cooper 998 had SP41 tyres. I had anticipated it being delivered on cross plies and had told the supplying garage to fit Dunlop SP3 tyres if that was the case. When it came on SP4's, I kept these until they wore out, then fitted the medium pattern SP3.
The SP44 came later in Mini size in around 1966. It was the first radial M & S tyre in Mini size, followed by the Goodyear Ultra-Grip.
