what are the widest tires you can use front and back?

 

Let us start easy, what size wheels do you have or are you also changing the wheels?

 

Stock. Front is 90 90 19. Rear is 130 90 16 tire sizes

 

Or simply tell us what sizes your tyres are at present and if your bike is close to stock, or already customised.

 

Sorry. I will check the rims.

 

At the front, with your current rim, you are limited to very few different widths. Most modern bikes woth wide tyres use smaller diameter rims with low-profile tyres. Wider sizes available AFAIK are 100/90 and 110/90. Both will be a little wider, but also a little larger in rolling diameter.

At the rear your most limiting factor is clearance between tyre and belt. You may find you can get in a 140/85 (also known as MU) or 140/90. Bikes from that era don't have much scope to expand, without using custom modifications.