Thrust
Um, the Space Shuttle main engines about 500k pounds thrust X3 = 1.5 million pounds thrust plus two solid rocket boosters at 1.5 million pounds each for a total of 4.5 million pounds thrust at launch, all applied when the shuttle is at rest. As far as I know no astronauts have had to be sponged off of seats due to the acceleration. This rocket car should have no problem.