InSim bug report:

Dedicated server updates values of Speed, Heading, etc. in CompCar packets at a slow and variable rate.
The rate seems to depend on the amount of input the player driving the car makes.
With low input, such as driving in a straight line, it is About 0.5-1.3s .
With high amount of input, such as rapidly moving the wheel left and right, it can reach 0.05s ( if you try hard enough )
It was tested with MCI Interval of 50 and 100, on "pure" dedicated server and on dedicated server in the game.

With a non-dedicated server in the same conditions, everything is fine.

Why do I care? This bug seriously hinders development of my InSim program.

This is because a dedicated server does not run physics. The guest computers send "PosPackets" to the host more often when there are more input changes, and the host forwards these to the other guests. The PosPackets contain a lot of info about a car's state, like position, velocity, angular velocity, engine revs, gear, etc.

On the other guest computers the cars are run in physics (a low res version for distant cars and a high res version for nearby cars) between PosPackets, usually resulting in remote cars moving in a reasonably convincing way, apart from the little jerks every time another PosPacket arrives and corrects their position. Though sometimes those jerks can be big and there are known issues with extreme setups, but that's another story.

Anyway, on the dedicated server, only the position is updated between PosPackets (according to the velocity in the last packet). It's about the best a dedicated host can do really, because it is not running physics. So... not a bug.

Thank you for your insightful reply, everything is clear now I think I'll have to resort to polynomial approximations of coordinates.