The number in parenthesis is the max course length. It is calculated by the double of the last max score and/or some average of the previous max score. I see it go do the double of a new high max score, but will slowly go down if future generations do not improve on that value. All I know for sure is that when a model reaches that number it is stopped as having reached the 'max value'.

This morning I started a new evolution, started out at around 7% mutation with yielded my image above. I then jacked it up to 70% and the scores plummeted till both my raw score and the (X) values were near zip. Cranked it back down to 7% and I've been yielding some reasonably good numbers on at least a couple of the evolutions per set. Seems I have the best luck with fairly large and similar sized wheel designs with just enough clearance to avoid bottoming out on the peaks. Most of my better designs fail due to lack of momentum around score 238 on a particularly large climb. Also noticed that most of my better results have the shock pointed up on the front (lower COG and less bounce perhaps) and straight out to the back in the rear.