Quote from Peptis :

I think the problem with low frame rates isn't that the physics engine is slowing down but that you are receiving visual feedback with too much of a delay. That is, the state of the simulation on the screen is different to what is actually happening in the internal physics loop. This means that you could actually be making the wrong inputs as you're reacting too late.

Thats what I was trying to say

Anything below about 30fps and you will start to get visual stutter and this will effect your visual queues which is a MAJOR factor in your driving in LFS.

The higher FPS the better as your eyes will tell you that everything "feels" more smooth, also the faster the car the higher you want the fps as the car travels more distance per second so the more updates you want.

The other key thing that many overlook is that slower consistent FPS is better than FPS with a top end which is faster but jumps around. You WILL notice jumps in FPS far more than slower FPS.

I run on a lappy so lock my FPS at 40. It drops to 30 on a full grid but is capable of far more than 40 but 40 is my average so I lock it there. This gives a far more consistent game environment.