You think the street races are wild, watch a real off road downhill race some time. Truly insane! I used to race downhill and cross-country in the old days (late 80's) when there was no suspension at all... I remember crossing the finish line of the Mammoth Mountain Kamikaze at about 40 miles per hour on a blown out rear tire....
Now the courses are so rough they use 10 inch travel super bikes...