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Issues that come off the top of my head include:
1.) Lower efficiency
While motors (especially the AC variety) tend to have very linear torque curves, they have a speed of most efficient operation. Using a hub motor, which almost certainly means it will be direct drive, forces the motor to operate under a much wider speed range. Generally, the faster the motor turns, the lower its efficiency due to friction.
Many of the top solar cars use direct drive hub motors, though. I've forgotten the motor brand, but it is extremely expensive for its output and extremely efficient.
2.) Higher Unsprung Mass
Hub motors are physically attached to the wheels, increasing their weight. From a performance and design perspective, lowering the unsprung weight to sprung weight ratio is desirable. Heavy wheels exert large forces on suspension members, causing their required strength (and thus weight) to increase.
3.) More Complex Drivetrain
Some high-end electric cars, such as the Tesla Roadster, use hub motors. The average DIYer most likely shies away from the technology because it is easier to drop in an engine replacement than redesign the drivetrain. Axles would have to be lost, kingpins and steering knuckles redesigned to accomodate the motor and its wiring, and special rotating electrical contacts fabricated to power the hub motors. While it is not impossible, hub motors probably rate low on the cost/benefit ratio list.
- LostCause
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