During the fight between Arjuna and Karna in the Kurukshetra war, Karna's chariot moved backwards by more than 7 steps when Arjuna's arrow hit the chariot, while Arjuna's chariot moved backwards by only two steps when Karna's arrows hit.
Krishna applauded Karna. To this, Arjuna asked that why was Krishna applauding Karna when he was able to bring back the chariot only by two steps. Krishna replied that on the chariot, Mahabali Hanuman was sitting, Krishna himself was sitting; even then Karna moved the chariot backwards by two steps; Krishna also asked Arjuna to imagine what would have happened if they were not on his chariot.
Now, my question is: Hanuman was in the flag of the chariot and he was without a material body. If the weight would have been too great, then how did the horses pull the chariot?
Taking into account these facts, then what is so special about Karna being able to move the chariot?