VehicleMovement Drag Force wrong direction

VehicleMovementComponent → Drag Force Parameter

The drag force should simulate air drag force and slow the car down at high speeds

Bug: The Drag force is not applied on a local vector of the car [-X], but on a world axis [-X]. This leads to drifting while driving parallel to the world [Y] axis, or crazy accelleration while driving in world[-X] direction.

Notice: This effect can only be seen with fast moving cars, or cars of extreme low mass. I myself needed 3hours to figure out why my car was drifting always in world[-X] while driving on ice (low tire fraction)

How to repruduce:

  1. Create a WheeledVehicle BP

  2. Import a car, set everything up (the car from the content packs will work too, if they use a vehiclemovementcomponent)

  3. Change the mass inside the VehicleMovementComponent to a low value like 10kg. This will make sure, you can see the effect. You might also set the tire friction a little lower like 0.4

  4. Make sure VehicleMovementComponent->“Drag Force” <>0 (higher values work better)

  5. Auto Posses Player 0 in game, drag car into a level.

  6. Play the game. Align car to World Y-Axis and speed up. The faster the car goes, the more it will be dragged to World [-X] Axis.

  7. If you can’t reproduce, build a little ramp aligned World Y-Axis. The Tire Friction may cause the issue. If no tires are on the ground or the front wheels lift a little when going full throttle, the effect will be seen much better.

best regards, Tank

Sorry, the value is called “Drag Coefficent” and not “Drag Force”. You can find it:

VehicleMovementComponent->VehicleSetup->Drag Coefficent


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