Hi,
There are several ways but I am going to mention one that I use very often and works well:
For each of your cars, you will adopt a set of convention:
at the top most Object, you will have an Fsm called "Meta Data", this FSM wil do nothing but host some variables ( your wheels objects or colliders, some properties like maximum speed, etc etc)
Then inside the car, all the Fsm dealing with specifics will ALWAYS refer to this Meta Data to access these properties.
This way, anywhere you are an don any of your future car prefabs, your logic WILL rely on the fact that they expect a "Meta Data" Fsm at the root of their instance and that it will have the variables it expects.
To access metaData, you'll use the actions GetFsmXXX and alwasy store the metadata value into a local variable for your Fsm, For clarity you could adopt a convention, so all local variable that have a value that is coming from the MetaData could start with # so MetaData:FsmVariable "Front Right Wheel Collider" will be called in any other fsm that needs to get this value "#Front Right Wheel Collider", then in the long run, you know where you are when you look at logics at a glance.
Does that make sense?
Bye,
Jean