The truth on Tigers and Panthers:
"It is suggested to the Red Army to use such German tanks as StuG III and Pz IV due to their relability and availability of spare parts. The new German Panther and Tiger can be used until they broken down without trying to repair them. They have bad engines, transmission and suspension." - Department of Weaponry of the Red Army, late 1944.
http://www.achtungpanzer.com/tiger.htm