alloy size

OK - maybe a silly question and apologies in advance......

Thinking of changing my alloys as there is a lot of air in the wheelarches. Punto Mk2b currently with Fiat 15" and 195/45 15 tyres (which seem quite low profile)

If i put 17" on, then if i want to keep the same radius i will be shoeing it with 4 black rubber bands.

If i don't go for such low profile tyres then wheel circumference will change so will speedo over or under read - (can this be adjusted) also the car will be sitting that much higher as overall diameter and radius has changed.

Whats the best option?

Thanks.

an increased wheel radius will cause under-reading, can't help on the rest

205/40/17"s are the tyres you'll need
if you have a 1.2 you'll notice a drop in performance due to the increased tyre size , 16"s would be best
the car will sit higher and look like a 4x4 if it's not lowered on 17"s
17"s on a 5dr will rub on the rear arches, ok on 3dr
the speedo on my jtd on 14"s read 4-5mph over, on 17"s only 1mph over