yes i used the picture you provided to try and model it. i too can't replicate that with the curves you provided. that is what i was trying to show you in the last layer of the file i attached (labeled beam). the beam and the surfaces don't intersect. so somethings got to give. either your initial curves have to change or the beam is going to make some really funky changes.

i used the same method burrman showed. i used them years ago as well. those are standard nurbs practices. they work as long as you have good curves to start with. a different user was trying to model a boat awhile back. he had the same issues. without good starting curves, you won't get anywhere.

for complex models like the one you show, expert subd practices may be better. nurbs is good for simple stuff. but when you start getting super complicated nurbs becomes unbearable. this could be one of those cases. if you look at many modern cars, they have a lot of complex curves that would make nurbs impossible. the hovercar i showed, which was easy using these methods, is very simple. nothing complicated is going on.

what i mean is, you can define any given surface with four or five curves. using 2 rail sweep, patch, curve network, curve from edges etc... nothing is going to be exceptionally curved in multiple directions. or require tons of curves to define. it's best to sketch the curves in three different planes and use the curve from 2d. this way you can easily edit the curves. your wheel wheel shouldn't really be there. that should be the last thing you do with a split or trim command. it's also a little high. it makes the fender have an odd kink in it. but i tried to keep what you had and then add the beam. it doesn't seem possible to me.