From the Audi press release:
"The reference value for the new model designations is the power output of the individual model in kilowatts (kW). Audi is thus subclassifying its model range into different performance levels – each identified by a two-numeral combination. For example, the numeral combination “30” will appear on the rear of all models with power output between 81 and 96 kW. And “45” stands for power output between 169 and 185 kW. The top of the Audi model range is the performance class above 400 kW, which is identifiable by the number combination “70”. In each case the numerals appear along with the engine technology – TFSI, TDI, g-tron or e-tron.
The changes will kick off with the new Audi A8 generation in the fall of 2017. First among the two six-cylinder engines to be redesignated will be the 3.0 TDI with 210 kW – as the Audi A8 50 TDI, and the 3.0 TFSI with 250 kW – as the Audi A8 55 TFSI."
Above: Audi's new naming system on the A8
On the face of it, this new numbering system aligns Audi with Mercedes and BMW, who also use a series of numbers to denote the relative power outputs of their model variants.
Historically, the model designations for Mercedes and BMW would be based on engine displacement. The underlying logic behind this was the assumption that the larger the engine, the more power it produced. Thus, 'E300' would would mean an E-Class with a 3.0L engine and '320i' would be equivalent to a 3-Series with a 2.0L engine. Although this is no longer the case (for example, the new E300 uses a higher-powered 2.0L engine) the long-running use of this type of nomenclature by both brands means that customers are still familiar with the underlying logic behind the system. A customer who walks into a Mercedes dealership may not know the size of the engine in the E300, but they will understand that it's a more powerful car than the E200. A decades long history of using the same basic system develops a contextual familiarity for the customer.
Audi's new two digit numbering system is a stark departure from the previous system where the engine displacement was directly labelled. Without the historical precedent that Mercedes and BMW share, the Audi customer cannot be expected to understand what numbers such as '30', '55' and '70' mean. Moreover, with the industry focusing on electric vehicle development, other characteristics such as range (i.e. the distance the car can travel between charges) also become important, which is a metric that is not described by the new numbering system.
Overall, I feel that this new 2 digit numbering system is too little, too late. The system is too simplistic to cover characteristics that will be important in the future, such as vehicle range. Without historical precedent, it is likewise confusing for future prospective Audi customers.
With cars having a number of important performance characteristics such as power, torque, acceleration and range, it is difficult to concisely and clearly express all of these into a single alpha-numeric combination.
Perhaps a better option would be to scrap this model designation system entirely and instead follow the Ferrari route. Focus on marketing (and badging) the model only, e.g. Audi A4/A6/A8 and tabulate all performance characteristics on a hidden plaque or badge inside the car, together with any customer ordered options and other specification such as paint colour and wheel design. This way, all performance characteristics can be clearly displayed and understood. Additionally, this system would be beneficial come resale time, as all customer ordered options and preferences would be evident (with personalisation being key at the premium end of the market).