I just had Pirelli Tires installed and don't like them. What you you recommend 185/65/15 or 195/65/15?
185 i/65R15 is the Toyota spec'd tire; installing 195'65R15 will theoretically increase radius of the tire by 6.5 mm (~1/4"), which will have ramifications, such as drag increase, stability reduction, through off the odometer. All slight, but... It will increase ground clearance of course, again, a slight amount.
The OEM 185/65/15 tire actually causes the odo to read slightly higher than actual land speed. (ie speedo shows about 62ish when real speed is 60) Going to a 195/65/15 makes the odo almost dead nuts accurate to actual speed. For a G2 prius, any stability change isn't noticeable. MPG will drop slightly, some due to the new odo vs actual speeds, some due to the 195 tire usually being slightly heavier, some due to the car sitting slightly higher.
No, the computers know the true speed (approximately), but intentionally overreport speed with the speedometer, in part due to legislation: the object being to ensure drivers are never going faster than the displayed mph. More importantly, the computers also record, and display, the odometer value faithfully, IF you stick with the stock size. In short, going to a larger diameter tire to "fix" the speedometer, is the tail wagging the dog, throws everything else off.
