Computer Aided Engineering (CAE) FEA Case Study: Results Minimum Principal
Minimum principal stresses - compressive stress 
Minimum Principal Stress: The key (colour bar) has be altered to read from 0 to -100MPa. Everything that can't be seen is positive or tensile. The lower spokes on the the inside, (below the hub flange) and on the outside (above the hub) are compressive at around -50MPa. These are very low and insignificant. Compressive stresses may be higher than tensile stresses - much higher in some circumstances. A judgement has to be made as to whether very high compressive stresses are significant. For example, the bolts holding the wheel to the hub will induce massive compressive stress on the bolt loading surfaces and hub mating surface of the wheel. These are usually not an issue though, since we know the wheel doesn't usually break when the wheel bolts are torqued up!
Displacement: Since the maximum displacement is in the spring element, (to be discussed), the strain in the wheel is very small, but large enough to induce the compressive stresses shown. (Strain is directly proportional to stress).