Heavy lorries and trailer combinations cause many serious traffic accidents. There in Finland alone have been approximately100 killed per year by heavy duty vehicles in 1990's. Improvements in inspection methods of brake systems increase traffic safety. In Finland dynamometer measurements have been used since 1960´s, and its advantages are stable measuring conditions, high repetability and short inspection time. The Finnish Traffic Office and the Finnish Motor Vehicle Registration Centre have been interested in correlations of road retardation and dynamometer measurements and therefore established Dynamet-brake research project in 1993.This paper contains a research which aims to find out correlations of retardation prediction for lorries and trailer combinations by comparing road braking tests and dynamometer measurements, and secondly to improve the dynamometer measurement system at inspection stations. The research material consists of over 200 road brakings and nearly 150 dynamometer measurements. The road brakings and dynamometer measurements were performed at the Finnish Motor Vehicle Registration Centre's inspection station in spring and early summer 1995. The test vehicle used was a 3-axle lorry and a trailer equipped with traditional air pressured brakes, steel leaf springs and loaded by logs.