diff --git a/src/modules/simu/simuv4/susp.cpp b/src/modules/simu/simuv4/susp.cpp
index 8c2e51d41..03164bd05 100644
--- a/src/modules/simu/simuv4/susp.cpp
+++ b/src/modules/simu/simuv4/susp.cpp
@@ -96,15 +96,16 @@ static tdble springForce(tSuspension *susp)
 
 void SimSuspCheckIn(tSuspension *susp)
 {
-	susp->state = 0;
+	/*susp->state = 0;*/
+	/* note: susp->state is reset in SimWheelUpdateRide in wheel.cpp */
 	if (susp->x < susp->spring.packers) {
 		susp->x = susp->spring.packers;
-		susp->state = SIM_SUSP_COMP;
+		susp->state |= SIM_SUSP_COMP;
 	}
 	susp->x *= susp->spring.bellcrank;
 	if (susp->x >= susp->spring.xMax) {
 		susp->x = susp->spring.xMax;
-		susp->state = SIM_SUSP_EXT;
+		susp->state |= SIM_SUSP_EXT;
 	}
 }
 
@@ -113,7 +114,7 @@ void SimSuspCheckIn(tSuspension *susp)
 
 void SimSuspUpdate(tSuspension *susp)
 {
-	susp->force = (springForce(susp) + damperForce(susp)) * susp->spring.bellcrank;
+	susp->force = (springForce(susp) + damperForce(susp) + susp->inertance * susp->a) * susp->spring.bellcrank;
 }
 
 
@@ -136,6 +137,7 @@ void SimSuspConfig(void *hdle, const char *section, tSuspension *susp, tdble F0,
 	susp->damper.rebound.C2 = GfParmGetNum(hdle, section, PRM_FASTREBOUND, (char*)NULL, 0.0f);
 	susp->damper.bump.v1    = GfParmGetNum(hdle, section, PRM_BUMPLVEL, (char*)NULL, 0.5f);
 	susp->damper.rebound.v1 = GfParmGetNum(hdle, section, PRM_REBOUNDLVEL, (char*)NULL, 0.5f);
+	susp->inertance = 0.0;
 	
 	susp->spring.x0 = susp->spring.bellcrank * X0;
 	susp->spring.F0 = F0 / susp->spring.bellcrank;
diff --git a/src/modules/simu/simuv4/susp.h b/src/modules/simu/simuv4/susp.h
index 4f3abb1aa..e81bfffd2 100644
--- a/src/modules/simu/simuv4/susp.h
+++ b/src/modules/simu/simuv4/susp.h
@@ -48,15 +48,17 @@ typedef struct Suspension
 {
     tSpring spring;
     tDamper damper;
+    tdble inertance;
 
     tdble x; /* suspension travel */
     tdble v; /* suspension travel speed */
+    tdble a; /* suspension travel acceleration */
 
     tdble force;        /* generated force */
     int    state;        /* indicate the state of the suspension */
 #define SIM_SUSP_COMP   1  	/* the suspension is fully compressed */
 #define SIM_SUSP_EXT    2  	/* the suspension is fully extended */
-
+#define SIM_SUSP_INAIR  4   /* the suspension is in the air, can be combined with the other states */
 } tSuspension;
 
 
diff --git a/src/modules/simu/simuv4/wheel.cpp b/src/modules/simu/simuv4/wheel.cpp
index 91d98bfe3..a87d118bc 100644
--- a/src/modules/simu/simuv4/wheel.cpp
+++ b/src/modules/simu/simuv4/wheel.cpp
@@ -160,19 +160,29 @@ void SimWheelUpdateRide(tCar *car, int index)
     tdble max_extend =  wheel->pos.z - Zroad;
 	wheel->rideHeight = max_extend;
 
+	if (car->features & FEAT_FIXEDWHEELFORCE) {
+		if (max_extend > new_susp_x + 0.01) {
+			wheel->susp.state = SIM_SUSP_INAIR;
+		} else {wheel->susp.state = 0;}
+	} else {
+		wheel->susp.state = 0;
+	}
+	
 	if (max_extend < new_susp_x) {
 		new_susp_x = max_extend;
 		wheel->rel_vel = 0.0f;
 	} else if (new_susp_x < wheel->susp.spring.packers) {
 		wheel->rel_vel = 0.0f;
 	}
- 
-	tdble prex = wheel->susp.x;
-	wheel->susp.x = new_susp_x;
 
+	tdble prex = wheel->susp.x;
+	tdble prev = wheel->susp.v;
+	wheel->susp.x = new_susp_x;
+	
 	// verify the suspension travel, beware, wheel->susp.x will be scaled by SimSuspCheckIn
 	SimSuspCheckIn(&(wheel->susp));
 	wheel->susp.v = (prex - wheel->susp.x) / SimDeltaTime;
+	wheel->susp.a = (prev - wheel->susp.v) / SimDeltaTime;
 	
 	// update wheel brake
 	SimBrakeUpdate(car, wheel, &(wheel->brake));
@@ -210,13 +220,10 @@ void SimWheelUpdateForce(tCar *car, int index)
 	// VERTICAL STUFF CONSIDERING SMALL PITCH AND ROLL ANGLES
 	// update suspension force
 	SimSuspUpdate(&(wheel->susp));
-
 	// check suspension state
 	wheel->state |= wheel->susp.state;
-	if ((wheel->state & SIM_SUSP_EXT) == 0) {
-		wheel->forces.z = axleFz + wheel->susp.force;
-		if(wheel->susp.force > 0)
-			{wheel->forces.z += wheel->axleFz3rd;}
+	if ( ((wheel->state & SIM_SUSP_EXT) == 0) && ((wheel->state & SIM_SUSP_INAIR) == 0) ) {
+		wheel->forces.z = axleFz + wheel->susp.force + wheel->axleFz3rd;
 		reaction_force = wheel->forces.z;
 		if (car->features & FEAT_FIXEDWHEELFORCE) {
 			wheel->rel_vel -= SimDeltaTime * wheel->forces.z / wheel->mass;