Actually, if you are driving a real car, you will step on the
brakes first to decrease the RPM of the engine before downshifting.
An example will be your car's RPM is reving at 7000 RPM and you
would like to slow down, so the correct technique is to step on the
brake first to bring the RPM down to about 4000 - 5000 RPM before
downshifting. At 4000 - 5000 RPM, if you downshift, your RPM will
jump back to 7000 RPM again .. So, if you were to downshift at 7000
RPM, your RPM will shoot up to 9000 or even 10000RPM and will
definitely damage the engine or even blow the engine. The RPM range
also depends on your gear ratio..