If you've decided to swap from two wheels to four or vice versa, you could be disappointed. Bikes are statistically more dangerous than cars, meaning that linking an NCD in one vehicle type to another is difficult. For example, five years of driving a hatchback is very different to the driving you'd be doing on a 500cc Yamaha.
Therefore, check if any (full) years of NCD can be passed over before purchasing insurance. If using both a car and a bike, you'll probably need separate insurance for both.