Plus sizing is when the tire and wheel combination is changed out for a larger wheel and lower profile tire. It is a popular option since most people like the look of a larger wheel. But it is important to know that plus sizing your wheel and tires will also change the performance of the vehicle.
Typically, a small increase in wheel diameter will mean more responsive handling because of the shorter sidewall. For drivers that like sport driving and high performance cars, then a plus one fitment will have a noticeably positive impact on the ride quality. Conversely a large increase in wheel diameter can degrade the ride quality and handling of the vehicle.
Extreme plus sizing of 3 or more inches of wheel diameter will negatively impact the ride and handling of the vehicle since plus-sizing involves combining larger wheels with shorter, wider tires. For example, to plus size a 17" wheel, you would buy a new 18" wheel. As with any plus size, the overall diameter of the tire must be equal to the original tire and have the same or greater volume of air to support the weight of the vehicle. Therefore, the tire on the 18” wheel must have a shorter sidewall and a wider section width. The shorter sidewall ensures that the overall diameter is respected, while the wider tire compensates for the lost volume of air due to the decrease in tire profile (height).
Most experts agree that it is best not to plus size more than 2 inches. A sidewall that is much shorter will not flex as much as a tall sidewall, and the greater width can make the tire float too much on wet and snowy roads. This could lead to a loss of traction on dry roads, and the risk of hydroplaning on wet roads. Very short sidewalls often lead to broken wheels as the tire cannot absorb as much of the impact from pot-holes and other road hazards.
It you do elect to change out the wheels and tires for plus sized custom wheels, you must get the advice of a tire professional. A tire professional can easily find the right wheel and tire size to give you the look you want, while keeping your vehicle performing safety.