Obviously it depends a lot on the To/From addresses and also the size and weight of the wheels, but here are some suggestions:
- Shipping to a commercial address may be cheaper than to a residential address. (E.g. an office)
- Get quotes from all the carriers: USPS, UPS, FedEx, etc. In my experience USPS tends to be cheaper for smaller packages and FedEx tends to be cheaper for larger packages, but YMMV.
- If you use FedEx you will get a better rate if you have a "FedEx account". Something like 20-30% cheaper. Signing up can be a bit of a PITA but it is free. Not sure if UPS has a similar discount.
- Try getting quotes for different weight combinations. When I had wheels shipped recently it was cheapest to do 2 boxes with 2 wheels in each, but I got quotes for 1x4, 2x2, and 4x1.