This behavior can be caused when certain Special Items are used against your car. For example, Guardian has a Special Item called Scramble Hack that will cause the steering to go crazy and send the car all over the track. And the new Supertrucks have various weapons - including Rage mode - that can send the opponent spinning or even push them off the track.
Secondly, check the rear tires for correct alignment on the wheel. If they are off the wheel, then nudge them back with your finger. Be sure to check both the outside and the inside of the tires.
If the tyres are properly aligned, then the rear tyres may be dirty. Use the included tyre cleaner to clean the tyres. If necessary you can also clean the tyre cleaner by holding it under the tap and letting it air-dry afterwards.
Finally, the track surface may need to be dusted before starting the next race.
Please view our helpful maintenance video for more information: