The bigger the rim/tire in the back the more unsprung weight. The speedo gets thrown off if the actual tire size is taller. Slight power loss is seen but if you are having traction problems and are using the bigger tires to help gain it its worth the weight.

Get some good rims that are a good bit lighter than you current rims and your good to go. Then get the speedo recalibrated after your first ticket. : )

Looks is ok but thats Ricey. HEHE Just kidding.