Lightweight wheels are a good thing, lower non-sprung weight is good for ride quality. Alloy wheels, I'm convinced they are actually heavier than the steel rim wheels they have replaced
There are two problems. Firstly, alloys tend to be much larger than steel wheels, and secondly, the overwhelming majority are cast. Cast alloy isn’t particularly strong so a large volume of material is required to produce a durable wheel.
Flow-formed alloys address the issue to an extent as the process produces a stronger material, which means less of it is required, which obviously means less weight. My last work car had flow-formed wheels and the spokes were particularly slender (which looks good too!).
The ultimate solution (as far as “traditional” alloys go) are forged wheels. I specced them on my Focus as an option, and despite being reasonably similar in appearance to the standard cast alloys they’re over 1kg lighter which is a lot in terms of un-sprung weight. Again, they look very nice as well!
Wheel tutorial over.
