[quote=So Boerd]
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It was invented, just not widely used as a way to augment transportation efficiency. The wheel is easymode to create (Nubian peoples/Ancient Egypt as well as sub-Saharan African groups). The axle and the physics behind it? Not so much. Wheels (and axles) gave way to an excellent method of ferrying goods cheaply from place to place (obviously), but African societal groups primarily relied on pack animals and human-powered delivery methods to ferry goods to predetermined destinations. This is more expensive and less efficient (in theory), which probably stunted economical (and therefore technological) growth. Other reasons cited for this diminished level of development probably lies in Africa's lack of easily-broken animals (you're not going to have much luck in domesticating something like an elephant and then having it till land; most you can do is tame it, which isn't going to cut it for farm work), African tribe's being close to ample food sources (jungles and roaming herd animals) and environmental factors that imposed limitations on wheeled transport usage and extended development.

Again, the idea that Africa didn't invent the wheel is a common (and stupid) misconception that is widely regarded as fact--much like the idea that Africans willingly sold other Africans into slavery (held at gunpoint by Europeans and under the assumption that European indentured servitude and slavery practices were similar to those of their own) or that they ate each other willingly (evidence for African cannibalism is sparse; you find more evidence of this occurring in Europe and especially with early settling efforts in the Americas). Ancient Nubians used the wheel for pottery.

EDIT: That above question wasn't supposed to be posted. Thanks Mahz.