A carcass reinforcement for a tire which is intended to bear heavy loads, comprising a composite fabric which comprises a rubber composition of reduced hysteresis and metal cables reinforcing the composition. The elastomeric matrix thereof comprises natural rubber or a synthetic polyisoprene in a majority proportion, and a reinforcing filler comprising a carbon black which meets all of the following conditions: (i) 45≦CTAB specific surface area in m2/g (in accordance with Standard ASTM D3765-80)≦70, (ii) 45≦BET specific surface area in m2/g (in accordance with Standard ASTM D4820-93)≦70, (iii) 45≦iodine adsorption index IA in mg/g (in accordance with Standard ASTM D1510-81)≦70, (iv) ratio (BET surface area/index IA)≦1.07, (v) 115≦DBP structure value in ml/100 g (in accordance with Standard ASTM D2414-93)≦170, (vi) 85 nm≦Stokes diameter dst in nm≦145, where dst is the diameter of aggregates corresponding to the maximum frequency of the Stokes diameters in a distribution of aggregates, and (vii) D50/dst≧0.0090. CTAB+0.19, where D50 is the difference, in the distribution of aggregates, between the Stokes diameters of two aggregates corresponding to one and the same frequency equal to 50% of the maximum frequency of the Stokes diameters, dst and D50 being measured by centrifugal photosedimentometry.