I have changed wheels and tires and wonder if it is necessary to have another alignment. It was aligned with 15 x 8 inch wheels with 4 inch backspacing. It now has 17 x 8 inch with 5 1/4 backspacing. The overall wheel/tire is the same diameter/circumference. Major difference is the backspacing, moving the wheel further into the wheelhouse front and rear.

Thoretically no since you didn't affect the stance of the car other than the diameter. In reality, the larger tires are so much more expensive, and an alignment is so cheap, do the math!

I didn't affect the diameter, only the backspacing on the wheels - they now sit 1 1/4 inches further inward.

ttt

66, Just changing wheels and tires, no matter how much bigger or smaller has no affect on wheel alignment. You may want consider having it checked however, if it has a been awhile since last alignment.