Side member (23) for a chassis (27) provided with a wheel (26) which side member (23) comprises an upper flange (32) and a lower flange (33). Both of the flanges (32, 33) of the side member (23) have a continuous extension along the whole of the side member's (23) entire length. The upper or lower flange (32, 33) exhibits two oppositely directed curved portions (38, 39) that are both located in front of or behind said wheel (26) so that the curved flange's (32, 33) perpendicular distance to the non-curved flange (32) at one end of the chassis (27) is greater than the corresponding perpendicular distance to the non-curved flange (32) at the other end of the chassis (27). The non-curved flange (32) and the curved flange (33) are connected to one another via at least one connecting member (40, 51, 52). The side member (23) is provided with a center flange (34) which is located between said upper flange (32) and said lower flange (33) and which extends from one end of said upper and lower flange (32, 33) to a region located between said two curved portions (38, 39).