In measuring the transient rheological response of fibre filled suspensions, the velocity gradient in the radial direction in a parallel-plate geometry imposes additional stress contributions. Likewise, the small gap at the centre of the cone-plate geometry introduces anomalies due to gap effects. In light of this, a modified cone-plate geometry has been designed with a radius and angle of 20mm and 0.1rad respectively and a larger truncation gap of 0.8mm. The larger truncation reduces the contribution from gap effects while imposing a constant shear rate across a larger area of the sample. By performing a theoretical computation, it was determined that the truncated region contributes approximately 2% of the total torque generated. Experimental measurements were performed with standard silicon oil to establish the accuracy of this geometry. In addition to transient viscosity and first normal stress difference at the start-up of flow were measured for a fibre-filled PA6 composite. The accurate measurement of first normal stress difference would be a useful input in theoretical analysis where the contribution of normal stress is significant to the overall stress. In this work, predictions of first normal stress difference obtained from rheological constitutive models that include fibre orientation evolution and fibre concentration migration are compared with experimental data.