The invention concerns to a method and arrangement for a suspension system that may be constituted by a harvesting trait of a forestry harvester and which suspension system is of the type that has a wheel supported and provided with an angle sensor in order to form a measurement wheel for the measurement of length, with an arm pivotably attached to a frame in such a manner that the wheel can be adjusted from positions in contact with and out of contact with a surface of the object whose length is to be measured while the object is fed in its longitudinal direction past the measurement wheel running against the circumference of the measurement wheel, whereby the said object may be constituted by a tree trunk taken up into a harvester unit.
