After 2 years of building electric racecars, AERO decided to build a hybrid racecar again. GreenSpeed 4, a “mode shifting” parallel-series hybrid, was brought to competition in 2015. It was awarded General Motors best Engineered Hybrid Award, but did not place overall.
| Type | Hybrid |
| Motor | (3x) Motenergy DLC-28 |
| Motor Type | PMAC |
| Motor HP | 50 hp @6000 rpm |
| Motor Torque | 74 lb-ft @ 0 rpm |
| Motor Controller | SevCon Gen4Size6 |
| Engine | KTM SXF 250 |
| Engine HP | 35 hp @ 10,800 rpm |
| Engine Torque | 20 ft-lbs @ 8,600 rpm |
| Batteries | 240x Grepow Battery Co GLPA042125 5Ah Pouch Cell |
| Battery Configuration | 24S10P |
| Battery Chemistry | LiPo |
| Voltage | 89 V |
| Burst Current | 2000 A |
| Capacity | 4450 Wh |
| Wheelbase | 73 in |
| Track Width | 72 in |
| Weight | 1150 lbs |
| Uprights | Polaris Front, Custom Rear |
| Wheels | Keizer Aluminum |
| Tires | Hoosier 20x7.5-13 |