It's time for me to get new tires, and I realized that I my car currently does not have stock wheels and tires on it. I am the second owner, so I'm guessing the first owner changed it. Although they are Subaru branded wheels, so I'm not sure why they changed to a different size....
Anyway, I've noticed for a while that my speedometer is a little fast. Radar speedometers usually put me 2-4 mph under what my dash says. I've never considered it a big deal, but I figured that now that I need to get new tires maybe I can attempt to rectify the issue (preferably without getting new wheels).
I'm looking at this tire size calculator. It lists my stock tire, followed by the size currently on the car, followed by the size I was looking at changing to. By all metrics it looks like the new size would throw things off more, except for the "Speedometer Reading" field. For that one, it looks like this new size would be better.
Can anyone explain to me why the circumference is 1.5% worse, but the speedometer reading is 1.5% better? Would switching be a good idea? Are there other considerations I should be making?