   Strange simulation when combining Box2D with SFML
I want to make a game using Box2D v 2.2.1 and SFML 2, but i have a little problem with the physic simulation, its act strangely and different from when tested using default testbed.I try to simulate the tire from behavior iforce.net tutorial that working well on the default testbed. my main code:...void GAME::GameLoading(){    testTire = new Tire(&_mainWorld);    _gameState = gs_Playing;}void GAME::MainLoop(){    ...    while (_mainWindow.isOpen())    {   switch (_gameState)   {  case gs_Loading:  { GameLoading(); break;  }  case gs_Playing:  { _mainWindow.clear();_mainWorld.Step(1/60.f,6,2); testTire->updateFriction(); DebugRender(); _mainWindow.display(); break;  }   }...    }}...b2Vec2 Gravity(10.f,0.f); //Make the tire moveb2World GAME::_mainWorld(Gravity);Tire* GAME::testTire; when i run this, the tire just move in x(gravity) axis with slow movement because the friction i made, but it wont move in y axis, i've try to rotate it a few degrees to but it doing the same. please help me fix the code, i have worked on it for five days and still didn't find any solution. Thaks  PS : Sorry for my bad english