[woodcote]

Digital lane-changers do have a tendency to catch any low-hanging parts of a car. A set up plate like this...

   

... is good to have - it's very flat and you can see through from the underside to find out what's going on. That Mitoos one is the cheapest Pendles sell here. Mine is a simple 9x17cm piece of 6mm thick clear acrylic - with a 4cm slot cut into the front short side and all the edges smoothed off (they can be rather sharp!). Here it is in action...

   

An alternative is to take a piece of track - which is never as flat as a piece of acrylic - but you can hold it all up to the light, have a look between the track and car and see what might be catching. It could be the gears, so have a long end-on as well - to see the areas obscured from the side by the wheels.

My hunch with a Scalextric car is that the chassis isn't straight. The easiest remedy is to ease off all the body screws a turn - if they are all completely tighten, it can warp the chassis so it rubs on the track. Loosening screws is pretty much the first thing I do to any Scalextric car. Take a look in the SlotRacer's Manual for more details -  or there's my Scalextric tuning posts on the Jadlam blog.

Let us know how you get on!