Tyranid hive ships deal less damage from ramming than they should. Their spurs most likely do not work.
A hive ship ramming a chaos cruiser takes about 465 damage.
The rammed chaos cruiser takes about 530 damage (It took 70 hull damage prior to the ram)
A hive ship with 67 armor, a spur and 2000 HP should not ram ~15% better than a 67 armor, chaos cruiser with 1600 HP. Testing against a 2000 HP ship would probably show identical ramming damage despite the hive ship having a spur.