21lbs isn't really "lightweight"... typically, many would say anything under 19lbs is more on the lightweight side. A lot of OZ and Enkei rims are very nice looking and low weight.
At the risk of asking a stupid question, is there any downside to having lighter rims (say going from the heavy Detroits to something weighing 20lbs or less)? For example, does it require revised spring rates?
Thanks!
Aside from possibly being weaker, not really any downside....spring rate is primarily(grossly simplified sense) concerned with body control of the car....not the unsprung side...