Proposal to modify performance calculations and limits under UN R55. Currently UN R55 prohibits a vehicle combination with required performance values Dreq, Dc-req, Vreq and Sreq where Dc-cert ≤ Dc-req ≤ Dcert and Vreq ≤ Vcert. However, a requirement combination such as Vreq = 0.1* Vcert and Dc-req ≤ Dcert +0.1*( Dcert – Dc-cert) better reflects the real-world situation commonly found in combinations comprising a rigid truck, converter dolly, and semi-trailer.