Constant Force causing my object to twist/veer off.

Hey there,

Am writing a simple game based upon cars street racing, ideally they need to go in a straight line with the occasional swerve to overtake something.

However one thing is bugging me that I can't sort out - when I apply a force to the rigidbody of the car (which atm is a Cube) the item moves down the Z axis but also twists and veers off course.

I don't want to use constraints to clamp the rotation (as I want to be able to steer the car) and it doesn't seem right that if you push something equally from behind, dead centre that it should veer off to the side.

I can reproduce this if I have a blank project with a cube, a floor and the Constant Force script too.