The Automation Core

EV Highway Range Explained: Same-Platform Jeeps 120 Miles Apart, a CdA and Tire Breakdown

· aerodynamic drag, CdA, Chevy Bolt LFP, drag coefficient, EPA range, EV highway range, Jeep Recon, Jeep Wagoneer S, rolling resistance, The Engineering Core,


Bottom line: Two Jeeps share Stellantis' STLA Large platform, the same 94 kWh battery and the same 335 hp front and rear motors, yet their highway range differs by 120 miles. The powertrain isn't what separates them. Body shape, tires and air are. Here is the energy accounting, built from Car and Driver's Oct 2 test and InsideEVs' Oct 8 Bolt report.

What happened

  • Jeep Recon Moab launch edition: 160 miles in Car and Driver's steady 75 mph highway test, or 1.7 mi/kWh, against an EPA estimate of 222 miles. C/D puts it among the least efficient of the 100-plus EVs it has run.
  • Jeep Wagoneer S, same platform: 280 miles and 3.0 mi/kWh in the same test, close to twice the efficiency.
  • Differences C/D lists: Cd 0.40 vs 0.29, frontal area 32.7 vs 29.1 ft², ground clearance 9.1 vs 6.4 in, and the Recon's off-road-leaning tires.
  • 2027 Chevy Bolt (65 kWh LFP): Tom Moloughney (State of Charge) ran steady speeds on the New Jersey Turnpike: 280.3 mi at 60 mph (4.1 mi/kWh), 243.1 mi at 70 (3.6) and 219.3 mi at 80 (3.2). EPA rates it at 232 highway, 294 city and 262 combined. C/D's own 75 mph run gave 230 miles, which sits right between the 70 and 80 mph results.

Drag-area check (my arithmetic): Recon 0.40 × 3.04 m² ≈ 1.22 m². Wagoneer S 0.29 × 2.70 m² ≈ 0.78 m². The Cd gap is only 0.11, but on a bigger frontal area it becomes about 55% more CdA.

Point 1: CdA, not Cd, sets highway consumption

Aero drag is F = ½ρ·Cd·A·v². Cd describes how clean the shape is; A is how big a hole you punch. Taking ρ = 1.2 kg/m³, no wind and 75 mph (33.5 m/s), the Recon needs about 820 N and the Wagoneer S about 530 N. Over one mile (1,609 m) that is 0.37 vs 0.24 kWh/mi at the wheels just to move air out of the way.

Point 2: Splitting the gap, and aero is only part of it

Inverting C/D's figures gives roughly 0.59 kWh/mi for the Recon and 0.33 kWh/mi for the Wagoneer S, a 0.26 kWh/mi gap. The wheel-side aero difference is 0.13. If the drivetrain (inverter, motor and reduction gear) runs at about 90%, that becomes 0.14 to 0.15 at the battery, or 55 to 60% of the gap. The remaining ~0.11 kWh/mi most likely comes from all-terrain tire rolling resistance plus underbody and ride-height flow effects that a single Cd number doesn't fully capture. That split is my estimate. C/D didn't publish it.

Point 3: Why the speed curve is flatter than v²

From 60 to 80 mph the Bolt goes 33% faster. If drag were the whole load, energy per mile would rise 78% (1.33²). Measured consumption went from about 244 to 313 Wh/mi, only +28%. Total consumption is a speed-insensitive base (rolling resistance, HVAC and 12 V loads, baseline drivetrain loss) plus an aero term, and that base dilutes the v² growth. It follows that the bigger a vehicle's CdA, the larger aero's share and the steeper its range falls with speed. That is my inference for why boxy off-roaders get hit hardest on the interstate.

Point 4: Why EPA numbers look conservative one day and optimistic the next

EPA's HWFET highway cycle averages 48.3 mph and stays under 60 mph. Most EVs then take the lab range times a 0.7 adjustment factor. So a Bolt cruising at 60 mph in mild weather can beat its EPA highway figure by nearly 50 miles. At 75 mph, though, the Bolt keeps about 88% of its EPA combined range (230/262) and the Recon only about 72% (160/222). Certification cycles rarely run at high speed, so the CdA penalty barely shows up on the window sticker.

Open questions

  • Neither report says clearly whether mi/kWh comes from the dash or from wall-side metering. The three Bolt runs back-calculate to about 68 kWh, above the 65 kWh rating, which suggests a different basis.
  • The Recon and Wagoneer S were tested on different days. Temperature, wind and tire pressure weren't published, and C/D's article gives neither tire specs nor the Wagoneer S curb weight.
  • The 90% drivetrain efficiency, ρ = 1.2 kg/m³ and no wind are my assumptions. Chevy hasn't published Cd or frontal area for the new Bolt, so I don't compute its CdA here.

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