Limiting the FPS ingame, well, for me anyway, is only useful when on a busy server and there are lots of cars nearby, as it stops the hideous fps drops that can happen when something big, such as a pileup, happens nearby, stuttering sound, slideshow screen for a few seconds, etc.. My usual FPS is about 75 fps, so i limit mine to about 40, which contrary to what people will say, is completely playable and perfectly adequate for lfs.
I have never had any image tearing while using any fps limiting, in LFS or any other game. Tearing usually happens if the graphics driver has a problem or the card itself is failing.