Try this:
Go to LFS' options > controls > axes / FF screen.
You will see yellow/blue bars on the left; these denotes the axes in your controller.
Move the left stick; you will see the corresponding axis move appropriately. Say this is "X axis", under "0". You will see that next to "Steer", the "0" is selected.
Now move the right stick. Hopefully a yellow bar will move. Say this is the axis next to "3".
Now you simply have to assign axis "3" instead of the "0" which is currently in place.
Click on "Steer" and now click on the axis that moved with the right stick ("3" as decribed in my example).
If I'm not making any sense what-so-ever, try the following animation which is given in the
LFS Manual
Hope you get it sorted!