The "engineering problem" is to design a vehicle that will be durable and responsive. ON top of that, people want it to look good too. Basically the hardware the vehicle is rolling on has to be able to support the mass and dynamic loadings resulting from that mass being driven around by us idiots in traffic. A few examples:
A tire; based on size, inflation pressure, strength of the materials it is constructed from, will safely support a given mass being driven around. Any MORE than that will cause the tire to flex excessively and overheat, at which point the layers of the tire material will start to come apart. Hence, tires have specific load ratings assigned by NHTSA (National Highway & Traffic Safety Administration).
A wheel bearing: the car makers don't design the wheel bearings on any of their cars. The car makers' engineer figures out the expected dynamic loadings on the bearing based on expected weight of the vehicle and how it will be driven. After adding in a safety factor (say 150%) the engineer then goes to Timken (or another industrial bearing manufacturing company that specializes in roller bearings) and gives them the 'specs' for the particular bearing he needs. "I need it to fit a shaft of diameter x, fit inside a hub of diameter x, be retained in a certain fashion, and support sustained face loading of xxxx lbs and sustained side loads of xxxx lbs, and I need 15,000 of them a week for the next three years". The bearing manufacturer, having already solved the specific detailed metallurgical problems of stress and wear and longevity of specific bearings, suggests a bearing (or designs a new bearing) that will meet the auto engineers needs.
Brakes: The auto company doesn't design brake systems. The auto engineer goes to the engineers at Brembo, or Aikebo, or some other brake manufacturer with the desired specs for a system. The brake specialty company then sets about designing a system that meets the specs of the auto company at a price they can agree on. When YOU go to the local auto parts store to get new pads & rotors, there are often several choices that will fit the specs of your braking system. Some will be designated as "Exact OEM Replacement". These are usually the ones that were offered to the auto manufacturer at the least cost to the automaker. It has nothing to do with quality, except that the part is usually guaranteed to meet minimum mfr specs and won't void the vehicle warranty.
Wheels: Obviously a single wheel lug will only supply a given clamping force at a design breaking strength. More lugs will provide more holding power. Heavier vehicles that carry more load need to have more lugs per wheel to maintain a desired safety factor. You COULD design a 1-ton truck wheel with four lugs, but each lug would be twice the diameter of a standard lug bolt, with accompanying larger nuts and wrenches. It's simply cheaper for the auto engineer to specify more lugs & nuts than to have a whole set of different larger parts for a different vehicle including larger lug wrenches that require more force to loosen (NOT something I want to deal with on the side of the road in a rain storm...).
Every mechanical part on a car is examined and designed in this way. Many parts are designed by the car company engineers and then made by suppliers outside the company. When you realize the magnitude of the task involved in designing a new car, it begins to sink in why it takes millions of dollars and so much time to accomplish.