There´s this Swedish site rullomkrets that can calculate the difference between tires and rims, I guess you can find a English somewhere.
The difference is in circumference.
Yes all speedos overread, but I think this is a little too much, I´m used to a max of 5km/h overread.
The radio plays CD and radio, but there´s no light so you don´t know what channel it is and you can´t setup anything.
Been trying to find a new 1 or 2 DIN radio dash, but it´s not so easy to find for this model and the car is a little old.