The kit comes with a mechanical speed control, which is really a three position switch operated by a servo, some of the RTR kits come with an optional Electronic Speed Control (ESC).  ESCs are available from many manufacturers.



    This is perhaps the first upgrade you should give to your car if it came with a mechanical speed control.  An ESC with Battery Elimination Circuitry (BEC) will eliminate a servo for the throttle and a separate battery pack for the receiver.  The BEC uses power from the car's main battery pack to power the receiver.  The ESC also allows for proportional control of the throttle unlike the mechanical speed controls which are all or nothing.  And some ESC's have a reverse or brake.  But the elimination of a servo and separate battery pack for the receiver is well worth getting an ESC.  Keep in mind that the ESC consumes a little bit of power itself.  There are two primary ratings for an ESC, one is the number of turns motor it supports and the other is internal resistance.  Other factors include pulse frequency, number of cell batteries it supports, and a reverse function or brake.  The lower the internal resistance, the less power it consumes and the less heat it produces.  The really low resistance models don't need a heatsink and are very small.  This Futaba MC800C Professional ESC is my favorite.  It has an internal resistance of only .00045 Ohms, supports 4-7 cell batteries, down to a 5 turn motor and has an optimal 3140 Hz pulse rate.