# Commission Regulation (EU) 2017/1151 of 1 June 2017 supplementing Regulation (EC) No 715/2007 of the European Parliament and of the Council on type-approval of motor vehicles with respect to emissions from light passenger and commercial vehicles (Euro 5 and Euro 6) and on access to vehicle repair and maintenance information, amending Directive 2007/46/EC of the European Parliament and of the Council, Commission Regulation (EC) No 692/2008 and Commission Regulation (EU) No 1230/2012 and repealing Commission Regulation (EC) No 692/2008 (Text with EEA relevance), Division 8: Calculating n/v ratios


n/v ratios shall be calculated using the following equation:
nvi=ri×raxle×60000∕Udyn×3,6
where:
nis engine speed, min– 1;
vis the vehicle speed, km/h;
riis the transmission ratio in gear i;
raxleis the axle transmission ratio.
Udynis the dynamic rolling circumference of the tyres of the drive axle and is calculated using the following equation:
Udyn=3,05×2 H∕W100×W+R×25,4
where:
H/Wis the tyre's aspect ratio, e.g. ‘45’ for a 225/45 R17 tyre;
Wis the tyre width, mm; e.g. ‘225’ for a 225/45 R17 tyre;
Ris the wheel diameter, inch; e.g. ‘17’ for a 225/45 R17 tyre.
Udyn shall be rounded to whole millimetres.
If Udyn is different for the front and the rear axles, the value of n/v for the mainly powered axle shall be applied. Upon request, the approval authority shall be provided with the necessary information for that selection.

---
Source: https://www.legislation.gov.uk/eur/2017/1151/annex/Sub/7/division/division/8. (the official version)
Page: https://openlegislation.uk/eu-regulation-2017-1151/annex-Sub/7/division/division-8.
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.