Considering that this is a rather a rounded triangle, I doubt it has anything to do with tightness, and more with convenience, esthetic. A symmetrical displacem

Considering that this is a rather a rounded triangle, I doubt it has anything to do with tightness, and more with convenience, esthetic. A symmetrical displacement is also slightly less constraining in term of keeping the overall circumference/periphery (i.e. less deformation). A better design would have been to flatten the wheel into an more oblong or even an egg shape, like snowmobiles or tanks have. However, it requires more mechanical displacement and adjustements.