16" wheels: TPMS & speedo questions

I finally got around to putting on the winter wheels and tires I used on my former Audi A3, with Dunlop Winter Sport 205/55/16 tires.

With the OEM Conti 225/45-R17s on my 2010 JSW, the speed read anywhere from 0 to 4 mph slow at different road speeds (not a linear error) and the odo seemed fine. With the 16s on the car, the speedo is dead on at all the speeds I tested today -- 35, 55, 70, each of which used to produce different amounts of error with the Contis. The odo seems the same, but I only drove about 10 miles, so that wasn't a thorough test.

Anyone have ideas about this odd set of circumstances?

Also, it took about 7 miles for the TPMS to notice the steelies have no sensors. Is that normal?

-dan

Try this calculator: http://www.miata.net/garage/tirecalc.html

Thanks, LeeM. The calculator shows a whopping .1" difference in diameter. So why does the speedo behave so differently with the 16s compared to the 17s?

-dan

If you had gone with 205/60-15 the % error would be 1.558E-4

245/45-17 OD = 25.681

205/60-16 OD = 25.685