Wide tyre kit

HY everybody…
I am seriously tuning my Vespa PX 150. In the first stage I will change the suspensions with Bitubo units, on the front will be instaled a Grimeca front disc brake kit (it will work fully hydraulic) and everything will be changed (lights units, turning signals, speedometers, a lot of chrome will be puted on etc etc)…
Now, in about a month I am going to tune the engine, and here comes the problem. With all those modifications I want a really better handling, so I want to mount a wide tyre kit on the rear and maybe even on the front. I would like to know what modifications will be necessary to fit the wide tyre kit on the rear and also when the handling will be better, when the wide tyre is only on the rear or when is on the rear and front.
Thank you

thank you very much for the explanation, I will order a wide tyre kit for the rear, and on the front I wil mount just a good normal sized tyre.

Good morning, at first: forget to mount the kit on the front wheel. You will slip much faster while bracking especially in curves. What you need to do aditionally depends on the size of the tire and  the size of the  rim. Sometimes tires with the same size but from a different supplier don’t fit.