You can fit a bike in the back seat of a car, but you must have to do some modifications for this purpose. You can carry out this by removing the front wheel and tuning the handlebar sideways. You can do this easily if the front wheel holds a quick-release skewer.
If you plan to fit a bike in the backseat of a car, you must do this properly. If you are planning to go off-roading and want to fit your bike in the backseat of a car, you can do this by following the instructions mentioned above.