Wondering,

Currently have 265 60 18 tires. Will 265 65 18 tires fit. I know they will be a little taller and throw the speedo off a bit.

 

Use a tire size comparison site like https://tiresize.com/comparison/

The width will be the same. Only the height will slightly increase. 1/2 an inch on the sidewall and 1.1" overall height. As you said, the speedo will be slightly off. Gets more off the faster you go. At 20 mph it will be off by .7 mph and at 70 mph it will be off by 2.5 mph. With only one inch of a difference between the overall size, it should not be an issue with fitting.

 

Thank you for the feedback about the tires.