Changes

*true (steerable wheels on given axle)

*axle (whole axle is rotated when steering, ''axle_model'' must be correctly defined, valid only for trailers).

|-

|steerable_lifted_axle

*trailer (hook, no weight transfer)

*spreader (removes the pitch degree of freedom, typical of a spreader/booster/stinger on a lowboy configuration)

|-

|axle_model