There is supposedly no import duty on motorcycle spares as such, they can charge you VAT , and a handling fee , is all.
I've brought in shocks, bash plates, tanks, pipes, bars, seats, pistons, filters, brake shoes etc in the last few years and have never paid duty.
Under the GATT agreement , all motor and motorcycle parts should be free of duty, I think. Tires maybe not, I dunno, there will be exception items no doubt , to protect local interest.