Thanks for that. It's a good start.
It might be a good idea to have a list of what alloys weigh what.
Ok this is just a cut and paste from wiki but..
"The amount of movement is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip when tracking over an imperfect road. For this reason, lighter wheels are often sought for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration; the irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence ride quality is deteriorated."