you can hit something going 40 and not break a thing.
then you next lap you hit something do 15 and you break a lower arm.
its all about physics on impact i guess. you know right angle, right spot,etc
you should be glad you didnt do more than thaat. i hiit a curb once with my old stampede and it snapped in half.

you should invest in a failsafe. if you go out of range your car will go immediately to full brake and save you some $.

do a search here and for failsafe and you'll see tons of threads about them.