I am using Spheres as wheels for the ODE Car ( hinge2 joints ) is it possible to use Cylinders instead.

The ODE manual has a section about common problems. It mentions problems with rotating bodies with non-spherical masses and some fixes for them.

However, you can use a cylinder geom and a sphere mass if you run into problems with cylinder masses. Given the fact that your cylinder revolves usually around the one and the same axis, you can have a spherical mass that has the same inertia around a specific axis by scaling the mass and the radius of the sphere. You can find stuff about this in various dynamics articles and books.

-Riku