hmmm....

s = (-giM/kaA)1/2


Seems like's it's missing a crucial piece. I think this should fix it:

s = (-giM/kaA)1/2 - FoSOP

where FoSOP = Fear of Splattering On Pavement

In my experience the difference between the first and the last one down a hill of any size is related more to who is riding the brakes vs. who is pedaling.