What is the proper percentage of air pressure for small cars tires?

I am sorry Tamara but there is no straight forward answer to your question. It is little more technical than one might think. Your consider some factors in figuring out how much you could inflate your tires. Firstll tire size, number of tires per hub (applicable in heavy duty trucks mostly), maximum speed rating and pressure spec's in psi. All these are clearly indicated by inscription on the tire you intend to use. You could go ahead and calculate using formula and there is chart for that as well. You could easily trace tire size to optimal pressure required. TIRE INFLATION EQUATION: Tire Weight / Tire Pressure = Load Capacity Pounds per PSI Example: At 80psi, a 265/75R1610ply itire will carry 3,085 pounds of load. At 60 psi on a 10ply tire, the tire's load carrying capacity is reduced to 2,314 pounds per tire. If the customer runs 65 psi in a 10 ply tire, his capacity is now able to carry 2,507 per tire.

From30 to 35 psi tire pressure not percentage

Most passenger cars will recommend 32 psi to 35 psi in the tires 

the ratio varies according to tire size