[Tri750]

I looked up the specs. on  the AM26 tires. this the width and diameter of stock, then next wider sizes for possible rear fitment.
90x90x18= 3.8"  24.4"
110x80x18=. 4.4"  25.2

110x90x18=  4.6". 26.1
120x80x18=. 4.7". 25.7
120x90x18=. 5.1". 24.6
The AM26 is such an awesome tire, I use them on my Interceptors and the CB350 Cafe.
They love wet weather, stick like crazy at track days and have a vintage look. Plus, they make them in many sizes.
For  aesthetics, I can see trying to bump up the rear tire. I did that on my 900F. I did have to put the brake stay rod in a press and sqooze it a bit to clear, but the result was nice. the bike handled great with the stock tire, I just wanted a chubbier rear.
I have also hurt the feel and handeling of bikes by plumping up the front tire. The steering gets heavy and slow.
Changing the front of a C5 to 19 would surely change the handling as described above, but it's all personal preference. Me? My plan is to be a G5 guy and to fit an exhaust, a MotoBatt sealed battery, big headlight and AM26's before it leaves the shop.

[Ducati Scotty]

Keep in mind, even if the tire fits in the fender it still has to "fit" on the rim.  While it may snap on an hold air, if your put too wide a tire on too narrow a rim it negatively affects the handling.  Since the beads of the tire are not far enough apart the tire does not take the intended shape and so it's not stable.  You can probably go a bit wider but check the wheel width and see what tires will fit.  Manufacturers usually spec minimum wheel width for their tires.  I agree, fatter tires look nice on the bike but too fat and you compromise performance and possibly even safety.

Scott

[r80rt]

http://www.dropbears.com/u/utilities/tyrerim.htm

[Ducati Scotty]

Thanks for posting that

[GreenMachine]

yes thank u...good info there...i take back all that vodoo about that red c5..

[r80rt]

I ain't taking down all the charms and hex signs !!