[speedsatya]

Originally Posted by sukiwa

Don't we need to consider overall diameter (OD) of tyre rather than sidewall to know speedo error.
205/55R16 has OD as 631.9mm whereas 225/50R16 would be 631.4mm, just an insignificant difference of 0.08%.

Yes ,OD will determine the speedo/odo readings.
I mentioned about the sidewall ,to show that the lower profile over the OE profile wouldnt matter much in this case