The Cafe' Tire thread should not be referenced for the stock sized rim....the rims/tires on those conversions is a completely different issue...those tires are a lower 70/80 aspect ratio and the rim is narrower.
Here is a thread that discusses the new tire options for the bike with the stock sized wheels.
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1448021014/0The stock rear rim is 2.75" wide. The available tire sizes fit the following rim widths.
130/90 2.50, 2.75, 3.00, 3.50
140/80 2.75, 3.00, 3.50
140/90 2.75, 3.00, 3.50
There is virtually no difference in the "suitability" of the tires based on rim width. The stock rim is always going to be at the lower end of the fitment guide - but all the tires sizes are approved for use on the stock rim.
The bottom line in the long tire thread is:
The stock 140/80-15 tires size is not common, and the only tire commonly available in that size is the stock IRC GS-18 tire....which is not all that great of a tire.
The 130/90-15 is almost a direct replacement. It is only about 1% larger in diameter, and the width measured nearly identical. I measured a stock IRC GS-18 on the rim and it was 132mm wide, and a Shinko 230 in the 130/90 measured 136mm when mounted. Handling, speedometer reading, etc. will not change. The tire visually appears to be the same size when mounted on the bike.
The 140/90-15 is a larger and heavier tire, and it looks noticeably bigger on the bike. The tire is 4% bigger in the circumference, and it does slow acceleration down a bit, slows the transition into and out of curves a bit and makes the bike a bit more stable in a straight line, and it will change the speedometer reading. Folks who ride mostly highways or use the bike to commute like the taller gearing and more stable ride. And if you put a lot of miles on your bike.....tires like the Michelin Commander can get you as many as 25,000 miles on a back tire (MMRanch).
You most likely will spend more time figuring out which "brand" of tire to buy....than you will what "size". If you are on a biking budget.....the Shinko 230 is a great buy in the 100/90-19 front & 130/90-15 rear tire combination.