I have an 07 jetta i recently bought and after placing my portable gps unit in the car i realized the speedometer is off so i checked the drivers side door frame for the factory size wheels and tires and from the factory it came w/ 255/ 45 r18 and what was on this jetta when i bought it is 255/ 40 R17 i just bought this car and the wheels are vw but 17"
my question is there a way to correct this problem without buying new 18" wheels and new 18" tires?

 

you could buy bigger 17" tires say a 255/50/17 that would put you at almost the identical heigth of the 255/45/18s that are recommended for your car according to your door jamb label. I think my calculations are right,but you should be able to get this info from a knowledgable tire dealer.