Try tp reduce sudden rotation after a collision, and reduce frequencies

of kart being pushed into the air.

src/karts/kart.cpp

@@ -2043,7 +2043,10 @@ void Kart::crashed(const Material *m, const Vec3 &normal)
         impulse *= ( abs_speed<10 ? 10.0f : sqrt(abs_speed) )
                  * m_kart_properties->getCollisionTerrainImpulse();
         m_bounce_back_time = 0.2f;
-        m_vehicle->setTimedCentralImpulse(0.1f, impulse);
+        m_bounce_back_time = 0.0f;;
+        impulse = Vec3(0, 0, 0);
+        //m_vehicle->setTimedCentralImpulse(0.1f, impulse);
+        m_vehicle->setTimedCentralImpulse(0.0, impulse);
     }
     // If there is a quad graph, push the kart towards the previous
     // graph node center (we have to use the previous point since the

src/physics/btKart.cpp

@@ -675,7 +675,7 @@ void btKart::updateSuspension(btScalar deltaTime)
         // force is used, which makes it much less likely for the kart to hit
         // the terrain, while when driving on flat terrain (length small),
         // there is hardly any difference
-        length_diff *= f*f;
+        //length_diff *= f*f;
         force = wheel_info.m_suspensionStiffness * length_diff
               * wheel_info.m_clippedInvContactDotSuspension;