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the kult of speed warboss says that it has the same rules as warbikes including a invulnerable save i havent seen it in a faw or errata. so my question is do all bikes get a 5+ invulnerable save?
It is not an invulnerable save, it is a cover save.
And no, not all bikes get a cover save, just ork warbikes with the specified rules.
"...a swarm of mechanised locusts sweeping over the land, stripping it bare of resources, bringing death and destruction to anything that stands in its path. Emperor preserve us against the predations of these so-called Orkish cults of speed!" - Cardinal Nomura at the Conclave of Hessen
look at the kos warboss on warbike. then say that
If he turboboosts i beleive he gets an invunerable save equal to his armor save
“Krump first, assk qweztions neva'!"- 3000 Orks
Dark Eldar- 1500 1/0/0
"the very gods for vengeance cry”- 3000 Dwarves
thats not what is said the exact words are: warbike: all special rules that apply to warbikes also apply to warboss on bike (5+ invulnerable save etc) note that warboss on a bike will suffer instant death if he is wounded by a strength 8 hit