I just did the calculation and my resistor dissipate about 25-26w of power 
does a PWM controller look like this HOSSEN® NEW 6V-90V 15A DC Motor Pump Speed Controller: Amazon.com: Industrial & Scientific ?
__________________
Best Tank (1557.2 Km): 2.57 LHK (91.63 MPG (US) )
Best Highway Trip (~36.8 Km): 2.16 LHK (109 MPG (US) )
Best Commute Trip avg (73.8 Km ): 2.33 LHK (101 MPG (US) )
 Echo-Troll Modding Thread
I know i dont have a very good write-up 
no lean-burn? no good gear ratio? p&g is the answer
MPG=1 TIME=0
|