|My aerodynamic rims. ; )|
Personally, I over-inflate my tires by 10-PSI. It creates less rolling resistance but it also makes the car feel stiffer. I do not endorse over-inflating your tires because it can cause to tires to explode and void any warranties you may have for your tires. Do this at your risk, I am not responsible for anything that may result from having over-inflated tires. An increase of 5 psi, should not be considered as "bad".
The aerodynamics of the tires can be further increased by having the wheel fully covered as shown in the picture. The last important thing is having tires with proper tire thread, they grip the road. A car that has no tire thread is dangerous because the tire may explode and they don't grip the road well. The expensive part is replacing all your tires. Whats your cars current PSI reading?