Can I put 245/65 /r 18 tires on my 1996 Buick riviera

The '96 Riviera came with 225/60r16 tires and they were 26.6 inches in dia. You need to stay close to that measurement to keep the speedometer correct and a larger diameter will rub on the bottom of the front strut spring mount. Going to 18" you need something like 245/45r18 which are 26.7 inches in dia. Depending on the rim you use, (offset is important) the 245 is roughly 1 inch fatter than the 225 so 1/2 inch more would be in the inside and outside, If you stick with Buick or Cadillac wheels, they both used some factory 18....I had a 2007 Lucerne with factory 18 so do some research.