Section 93(6)(c) in The Central Motor Vehicles Rules, 1989
(c)[ in case of vehicles having more than three axles, and fitted with or without retractable axle, wheelbase shall be the distance measured between the centre of the front-most axle and the centre point of rear combination of non-steered axles. [Substituted by Notification No. G.S.R. 625 (E) dated 8.8.2012 (w.e.f. 2.6.1989)]