I doubt I am the first to suggest this, but having vehicle brakes as a separate item, rather than part of the vehicle controls, seems like a good idea. My basic thoughts are as follows.
[ol][li]If you do not have brakes, you can stop either by rolling friction (same as if you dived from the vehicle) or, crudely, by engine braking (leg power, in the case of foot-crank vehicles). If you don’t have brakes, you don’t have a handbrake.[/li]
[li]Brakes attach to wheels. There would be three kinds of brakes that could be attached to any given wheel: drum brakes, disc brakes, and regenerative brakes.
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[li]Drum brakes and disc brakes would additionally need to be fitted with brake pads. These would range from crude (i.e. scraps of leather) to whatever modern, manufactured varieties you might prefer (and any homebrewed approximations thereof).[/li]
[li]Regenerative brakes would charge the batteries during braking, but would require special high-performance small electric engines to use as generators.[/li]
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[li]Total braking strength determines how quickly the vehicle can stop (up to a friction limit determined by the wheels). If the brakes are attached in a lopsided manner, the vehicle would be much more prone to loss of control on braking. Leather brake pads, racing brake pads, and brake pads that are too weak for the vehicle weight would wear out relatively quickly, but most of the time there will be little need to source replacements.[/li][/ol]
The two big improvements I see from adding these are, first, the additional verisimilitude and customization associated with finding, scavenging, and installing brakes, and second, the additional range on electric vehicles gained by regenerative braking.
