It is not very difficult to create a front suspension system for your real fx cars. You can use springs from Mini-z tuner Kenon. It is cheap to order a set of springs. (soft to hard) I recommend the soft pair of springs, so I obtain the best grip. The cars show a tendency to leave the sensortrack in peace-car mode. So the automatic steering will work much finer and the car still stays now on the track. In manual there is described, that a suspension is not necessary because the track is planar. But te most reason are the wires, which are more oval than round. the suspension is going on to compensate this error.
But first you need your kit for bearings. it is an advance to be the owner of a turning maschine. If not you, you know who has one. Make a shaft that you press in the left and right knuckle. There you can mount the 2 bearings each side. Open by boring the wirecenters to 6mmH7. ready! Reduce the diameter of the topper knuckle guide to the same diameter (2,80mm) for a length of 4mm, so the komplete length will be 6,50 mm.