Fix: Tractive effort was slightly too high as per NewGRF spec. (#6785)

src/ground_vehicle.cpp

@@ -58,8 +58,8 @@ void GroundVehicle<T, Type>::PowerChanged()
 
 	this->gcache.cached_air_drag = air_drag + 3 * air_drag * number_of_parts / 20;
 
-	max_te *= 10000; // Tractive effort in (tonnes * 1000 * 10 =) N.
-	max_te /= 256;   // Tractive effort is a [0-255] coefficient.
+	max_te *= 9800; // Tractive effort in (tonnes * 1000 * 9.8 =) N.
+	max_te /= 256;  // Tractive effort is a [0-255] coefficient.
 	if (this->gcache.cached_power != total_power || this->gcache.cached_max_te != max_te) {
 		/* Stop the vehicle if it has no power. */
 		if (total_power == 0) this->vehstatus |= VS_STOPPED;