RC car problem using bluetooth module
The HC-05 blurb states this: -


  This class 2 Bluetooth module comes programmed with firmware that
  allows it to pass the output of a serial communications port (default
  is 9600 baud) over a Bluetooth wireless connection with no software
  configuration


So, if you can create a data frame that uses say 5 bytes (or less) that incorporates speed and direction then keep sending that frame, you get a payload data update rate of 9600/(5 x 8) = 240 times per second.

So the problem isn't really about turning and moving at the same time but all about how quickly you can update speed and direction information.

Updating this information at 240 times per second should be OK for practically any RC car I would imagine.