According to :

Now, as if this thread was not already crazy enough, I got to
thinking.
If a person fills all the tires on their car with helium instead of
air, will the car be lighter on the ground and save fuel? (((Just a
thought))). Obviously the car would not float because it's too haevy
and there is not enough helium. If this worked at all, it would not
be a good idea in winter when weight is needed for traction on snow
and ice.

The car would be lighter by a few ounces or so - the economies of doing
this would be too small to be measurable. Helium ain't exactly
cheap either.

Of course if you filled the whole car with helium (after seriously
plugging all the leaks), would the car fly?

A few dozen cubic feet of helium won't lift a person, let alone
several thousand pounds of car.

This would not be a good
idea though because the driver would be talking like tweety bird on
his cell phone before he died a couple minutes later from lack of
oxygen..

Well, he could use a scuba tank, or an external air scoop ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.