[Nonfractal]

All good advice above,
A fix is not possible until the cause is identified.
To identify the cause, a setup plate is needed.

The quality of the toy brands is often poor.

The worst Scalextric car I've ever had to fix was scraping it's protruding motor "lump" part of the chassis on the track So badly that the car would not move.
An Aussie had bought this car for a pub race day and was perplexed and disappointed by it.

The wheels could not be changed because they were knurled press fit.
The tyres could not be replaced with larger ones because there was no space for that under the body.
The fix , eventually, was major surgery on the chassis, chopping out the motor lump with a modelling knife and replacing the aggressive magnet with one having less force.

Unfortunately, this is the kind of rubbish being produced at the bottom end of the market.

AlanW