Proposal to amend the tyre dimension requirements. The current rules for calculating the dimensional limits are not consistent among the UN Regulations for tyres and within the Regulations themselves. Hence they lead to uncertainty in the correct calculation. The current proposal aims at unifying the calculation rules to those used in ISO 4000-1 and all major tyre standards, e.g. ETRTO, Tyre & Rim Association (T&RA), Japan Automobile Tyre Manufacturers Association (JATMA).