How to fix extremely jerky movement on AI car?

Hi everyone,

I have a strange (maybe not so strange?) issue in which my AI car runs extremely jerkily unless I change Fixed Timestep to something as ridiculously low as 0.001. I can't work it out. I only have two cars with wheel colliders, physics updated in Fixed Update. The motion looks fine but when the AI car gets closer to the camera, it gets very stuttery, but just on that one car! Everything else is smooth, road movement, player car movement. I swapped the camera over, tested without the camera follow script, tried V-sync, nothing works!

I should add that this is a 3D behind the car view game.

I can't really interpolate the car's position, as I am using wheel colliders to propel it. Any ideas?