Wow, compairing a quad that is jumped and abused in the woods to a street bike is the worst. Like someone said, landing a jump or downshifting into a corner is **** on a motor, you don't see too many street bikers down shifting into a corner, usually they are easy and let the RPM's drop enough. It is 2 completely different things. Yes, they are motors, but we abuse motors worse than they do. Anyone know how often Street bike Racers (closed course) replace their valve train? It would be a good thing to look into.
No offense here, but you must have never watched ama streetbike racing. Aaron Yates, Matt Mladin and all the reat riders slam their bikes down gears all the time to get the speed to drop faster to get into corners. One image that comes to mind is Aaron Yates winning a 600cc class race heading out for the final lap with all the other racers right on his tail. Comes into a hard 90 degree turn downshifting so fast the bike is popping loud and tire is completely locked up and then bang he is gone. Downshifting is used in every form of racing. If anything it is harder on street bikes due to the fact their tires will not slip as easily as ours will. Remember dirt is forgiving and will allow you to slide as asphalt won't let you slide as easily. especially with tires that act like glue when heated.