I put in a 4 point harness, the downfall of this is the kid's are swapping buggies so much and the harness's require time/adult to adjust- safety first! My daughter can't pull the release on a 5 point yet. The engine sprocket 11t is the smallest I can get (the biggest that will fit is a 13t), the 37t is about the biggest that will fit without having to modify the carriage again. It's @ 3.36 ratio now, the Yerf is 2.58. That's pretty low gearing for the Punisher. Here's some brief entertainment of me this afternoon after we got done playing in the trails. After I watched the vid I was very happy with the stability- the tires stay on the ground pretty well.
http://www.youtube.com/watch?v=ehQa5gFqbGU
She thinks the kid's will drive like we do!!! My wife is very competitive but "FAR" from being dominant, she is mostly paranoid about the kid's getting hurt from excessive speed (rather the abrupt stop that occurs when hitting something a higher rate of speed) Great driving skills are developed young and mastered quicker. I want my kid's to out drive me!!!