Hi Seven, mpescatori here from Rome, Italy.
I have an '88 4-speed.
With the standard tire 140/80x15 and the standard belt drive I felt the bike was a wee bit short-legged, so I swapped to a 140/90x15, a wee bit longer legged.
At the same time, I went for the famous "chain conversion" and replaced the belt drive (2,96:1) with a 530 chain (you want a 530 over a 520 because of the torque of the big single) and 17/49 sprockets.
Final drive is now 2.88:1.
I thought going from 2.96 to 2.88 wasn't going to make much of a difference...
I thought going from a 140/80x15 to 140/90x15 wasn't going to make much of a difference...
...I thought...
I was wrong.
For starters, the speedo now underreads by at least 8%, so that if it reads... 55mph I'm actually doing at least 60-62...
...Oh, Hello, Officer, how's the weather ? Secondly, whereas I could previously putt-putt my way through traffic in 4th gear, I'm now stuck in 3rd... 4th gears is only good beyond 45-50mph.
So, take it from me, unless you only do slabside at 60mph, beware of altering your final ratios too much or else the bike will magically become a 3-speed...