A 2 m.p.h. error is very good, my 2014 Leaf has a 10% (approximately) error, that is true 30 m.p.h. is 34 speedo reading, 40 m.p.h. is 44 speedo, and so on.
Come to think of it my previous car, an ICE VW had much the same level of error, but both of these were marvels of accuracy compared to...