Please do your research before purchasing. This is a very complex motor system and should only be purchased by those who know exactly what they are doing and/ or are willing to figure it out :) 
This kit is rated at 3kw but can handle much more at peak. Be prepared to do a lot of custom wiring and splicing etc. Not for the novice!!!! Lets save us both a lot of time and energy :)
 
 
Item: QS Motor 3000W 138 70H Mid Drive Motor
Motor Type: BLDC Permanent Magnet Inner Rotor Motor With Hall Sensor
Brand: QS Motor, QSMOTOR
Motor Design: Single axle 
Matched Wheel: 12inch Wheel (as default)
Magnet Height: 70mm, 40pcs, 5 pole pairs
Diameter of stator: 138mm
Rated Power: 3000W
Rated Voltage: 72V as default
Speed: 100KPH 
No-load rpm: 3800rpm without flux weakening, 6000RPM with flux weakening.
Max Torque: approx 56N.m without Reduction ratio, approx 247N.m with 1:4.77 Reduction ratio  
Reduction ratio: 1:4.77 (as default)
Max Efficiency: 88%
Continuous Battery Current: pending (72V)
Peak Battery Current: 120A (72V)
Suggest Peak Phase Current: 450A
Thermic Probe: None as default (KTY83/122 is available, if you need, please let sales man know).
Working Temperature: Pending
Single Hall Plate with waterproof connectors
16mm² Cross Section of Phase Wire (not include insulation layer)
Hall Sensor Phasing angle: 120 degree
Waterproof Grade: IP54
Color: Black 
N.W./G.W.: 10.8kgs/11.5kgs   
Package Dimension: 34cm*34cm*33cm
Axle design to match with 428 sprocket, we will provide 428 14T sprocket as default.
includes 
1pcs X Votol EM150SP sine wave motor controller with standard CAN-BUS
motor
throttle
Wiring harness