Always the same speed is certainly a problem, on older devices some things don’t run at all because the moving models are too complex.
But maybe it can be achieved by limiting it to devices that display it in a range of 40 to 60 fps?
If by “bend” you mean that the object does not always stay in the same direction to the x,z plane (in sideways direction) , then that is easily possible with quaternions.
With the method I added
THREE.Quaternion.prototype.setFromBasis = function( e1, e2, e3 ) { …
see Car Racing - For lovers of fast cars!
you can set the orientation or bend as you like.
For the cars, I made it so that the road is always horizontal with respect to the sides of the road. For a real car race you could tilt the road accordingly in the curves.