site with wheel weights
http://home.earthlink.net/~cvlocas/wheels.html
there are several effects that happen when you change wheel sizes ranging from faster acceleration times (shorther length wheels or lighter units), slower acceleration (longer lenght wheels or heavier wheels), higher top speeds (longer length wheels), better cornering from wider wheels or tires
when you increase the weight of the wheel it leads to slower acceleration and increased braking distances with with more premature brake wear (increase in rotational intertia)...it also increases unsprung weight since the stock suspension was designed for the stock weights of the wheel
wheels mainly come in Length x Width...for instance stock honda wheels are usually around 15" x 5"...that's 15" tall and 5" wide
there are also ways to decrease overall length with tires...i.e. low profile units
when you change the rim or tire size it also changes your speedo since it was calibrated for the stock wheel combination...i.e. if the overall length increases then your speedo will show a lower speed when you are actually going faster...vice versa
the best combo is a slightly larger wheel than stock...moving from a 15" x 5" to a 16" x "6.5" unit that is lighter and wider than the stock wheel and keeping fairly aggressive tires...the whole package will weigh a little less than stock and give you much more grip for acceleration and cornering purposes without slowing you down and overtaxing your suspension
to get much more in depth...do a web search on unsprung weight and rotational inertia