With stock suspension (no lowering), I managed to fit 225x60x13 at the back which rubbed the inner guards only on the hardest speed bumps.
The front was restricted to 205x60x13 but only by fitting a spacer disk (which I NEVER use when pushing the car really hard around corners) and by cutting a tiny bit of metal off the
front bottom of the guard lip.

Offset is vital because it is a measure of how far the centre of the wheel is from the brake hub.
I now have 2 sets of rims (and much changed suspension), 1 for racing with MASSIVE offset (and huge cutouts+flares in the guards) and a normal set with an ordinary offset which can
fit inside normal guards.

Find a friendly wrecker who will let you try out many different rims and tyres.
Play until happy or he throws you out.

Your tacho will NOT be affected because it only counts engines revs, not tyre revs.
Speedo will usually vary about 10% for 13 inch tyres.
I.e. when the speedo say 100km/h, you will really doing more like 110km/h.

- Wayne S.