Changing tire size, regearing and computer update

[poppastar]

My '25 GT manual has 255/40x19 all around which are 27" in diameter. In time I'd like to go wider (and likely as a result ending up with summer tires).

I'm reading that the computer can be updated with Forscan for a change in tire diameter but all 4 have to be the same diameter and that there's no workaround to this? I'm thinking that can't be right so looking for some guidance here.

This might be the wrong forum to ask but I'm also looking to regear from 3.55 to 4.09. I've got a shop capable of it and my research indicates since I have a manual only Forscan is needed to updated the vehicle. Sound about right? Below is a screenshot from a Gemini search and my Iconic Silver Gt Nite Pony.

Thanks!

Sponsored

 

[Sofa King]

Same size front and rear are not required... DH and GT PP cars have 27" front and rear is 27.7.

Edit: biggest thing is to have the correct rear tire size in the computer.