Let Γ be one of the N2-dimensional bicovariant first-order differential calculi on the quantum groups Oq(N) or Spq(N), where q is not a root of unity. We show that the second antisymmetrizer exterior algebra sΓ∧ is the quotient of the universal exterior algebra uΓ∧ by the principal ideal generated by θ∧θ. Here ∧ denotes the unique up to scalars bi-invariant 1-form. Moreover, θ∧θ is central in uΓ∧ and uΓ∧ is an inner differential calculus.