4 lug pattern
weight: 38.5lbs with stock 175/60R16 tire
If you are wanting to reduce the weight of your iQ wheels significantly, you'll most likely have to move to 14 or 15" rims with a 185/70/14 bigger tire for instance.
You could move to 17" rims and smaller tires, but your curb weight is likely to increase and thinner walled tires are not recommended on the iQ.
You can also convert your rims from a 4 lug pattern to a 5 lug pattern with spacers.
These two piece conversion type wheel adapters are used to convert 4 lug vehicle with 100mm bolt pattern to fit wheels with 5 lug 4.5" (114.3mm) bolt pattern. They will also space out your wheels for 1.75-inch to help you get enough clearance for wider tires and rims.
A size 175/60 R14 tire weighs between 13 lbs and 14.5 lbs.
A size 185/70 R15 tire weighs between 16.5 lbs and 18 lbs
The lightest weight wheels I've found are made by Enkei