Which Kumho tire are you looking at? I'm pretty sure that the 716 comes in the 205/60R15 size.
The 55 tire is enough smaller in diameter that it will throw off your speedometer. It would be helpful to look up a tire calculator to see the difference. I used to have one bookmarked, but I lost it when my computer crashed a few months ago. Perhaps someone else has the URL for one.
Most tire spec charts give the tire specs along with the optimal rim width. They usually also provide a rim width acceptable range. The other specs, tire width, tire height, etc, are based on the optimal rim width. A wider or narrower rim will throw off the other measurements. A tire on a rim that is narrower than the optimal width will tend to wear in the center more. As long as the rim is still in the acceptable range, the center wear may not be significantly different. You may be able to partually compensate with slighltly lower tire pressure, but that is not really a good answer. My experience has been if the optimal width is within 1/2" of actual rim width, it is not significant. Anything more than 1/2" might be.
