Finally, new tires.
 

Finally had to buy new tires for the Sonata, also installed my hybrid Sonata wheels. Went from 205/65/16 to 215/65/16 and the difference so far is two mph, which means the speedo read correctly now. But the odo reads another 2.5% less.

The factory Kumhos lasted 50k and I am SO glad to be rid of them. The were loud new and VERY loud when worn. Replaced them with the Yokohama YK580 which gets great reviews. There very quiet, smooth riding and have a 51psi max:).

They roll very well, 3 mph better in my neighborhood hill coast test.
They fill in the wheel wells much better.

Only downside is even at 51 psi they are a shade soft on turn in response.

Can't wait to get some data...

Is there a diameter difference?

So the wheels on the hybrid sonata are wider than the "regular" car wheels? Or was there just better selection in the taller, wider size? How many RPM less is it turning on the highway?

Same size, 60 rpm less at a gps 65 mph.