If you tow a trailer with an electric vehicle, you already know the result: the range number on your dashboard collapses. A truck rated at 300 miles unladen might deliver 100–120 miles with a trailer attached. That is a 60–67% reduction. Understanding why it happens is the first step to solving it.
The answer is physics. Three forces act against the vehicle when towing — and at highway speeds, one of them dominates in a way that most EV owners don't expect.
Force 1: Aerodynamic Drag
Aerodynamic drag is the resistance a vehicle encounters as it pushes through air. The force it generates is described by:
Fdrag = ½ × ρ × v² × Cd × A
Where ρ is air density, v is velocity, Cd is the drag coefficient, and A is the frontal area.
Two things matter here. First: drag scales with the square of speed. Doubling your speed from 35 mph to 70 mph doesn't double your drag — it quadruples it. This is why EV towing range is so much worse at highway speeds than at city speeds. Second: drag scales directly with frontal area.
A conventional enclosed cargo trailer or boat trailer presents significant additional frontal area behind the tow vehicle. Even a single-axle utility trailer can add 30–50% to the combined vehicle frontal area. More frontal area means dramatically more drag — and at 65–70 mph, drag is the single largest energy consumer in the system.
This is the dominant cause of EV towing range loss. Not weight. Not hills. Aerodynamic drag at highway speed.
Modern EVs like the F-150 Lightning, Rivian R1T, and Tesla Cybertruck have sleek aerodynamic profiles — drag coefficients (Cd) in the 0.28–0.35 range. Hitching a conventional trailer behind them is like hanging a barn door off the hitch. The combined aerodynamic performance degrades substantially regardless of how efficient the truck is.
Force 2: Rolling Resistance
Rolling resistance is the energy consumed as tires deform and recover against the road surface. It scales linearly with the total weight on the road — adding a 4,000 lb trailer means 4,000 more pounds of rolling resistance to overcome.
Unlike aerodynamic drag, rolling resistance does not increase dramatically with speed (though it increases slightly). It is a relatively constant energy drain — significant at all speeds, but not the exponential multiplier that drag becomes at highway speeds.
At city driving speeds (25–35 mph), rolling resistance accounts for a larger share of total energy consumption — which is why EV towing range is less bad in city driving than on the highway. In stop-and-go city use, the proportional impact of drag is smaller, and the EV can also recapture more energy through regenerative braking.
In practice: a 3,500 lb trailer adds roughly 15–20% to rolling resistance energy consumption on level ground. Significant — but smaller than the aerodynamic contribution at 65+ mph.
Force 3: Grade Resistance
Climbing a hill requires lifting the combined mass of the vehicle and trailer against gravity. The energy required is:
Egrade = m × g × Δh
Where m is total mass, g is gravitational acceleration (9.8 m/s²), and Δh is elevation gain in meters.
Trailer weight matters enormously on grades. A 5,000 lb trailer added to a 6,500 lb truck nearly doubles the mass the drivetrain must lift against gravity. On sustained climbs — the Cajon Pass, Tehachapi Pass, the I-8 across the mountains east of San Diego — grade resistance can temporarily dominate energy consumption and significantly drain the battery.
The good news: what goes up must come down. Regenerative braking on the descent can recover a portion of the energy spent climbing. How much depends on descent grade, speed management, and whether the regen system is operating at high efficiency. Typically 60–75% of climbing energy can be recovered on descent through regen, but only if the battery has headroom to absorb it.
The Interaction: Why Highway Speed Is the Worst Case
At 70 mph on flat ground, aerodynamic drag accounts for approximately 60–70% of total energy consumption for a typical EV towing a recreational trailer. Rolling resistance accounts for 20–25%. At this speed, the trailer's aerodynamic contribution is enormous.
| Speed | Drag Contribution | Rolling Resistance | Typical Range Loss vs. Unladen |
|---|---|---|---|
| 35 mph (city) | ~30% | ~45% | 25–35% |
| 55 mph | ~50% | ~30% | 35–45% |
| 65 mph | ~60% | ~25% | 45–55% |
| 75 mph | ~68% | ~20% | 55–65% |
This table explains a common EV towing observation: slowing down from 75 mph to 60 mph dramatically extends towing range. Because drag scales with v², the 20% speed reduction cuts drag energy nearly in half (0.8² = 0.64). This is a real strategy EV tow vehicle owners use — and it works.
The Battery Side: Thermal and Current Effects
Beyond the mechanical forces, towing also stresses the battery system in ways that reduce effective range:
High continuous current draw. At highway towing speeds, the battery must supply sustained high power — sometimes near its continuous output limit. High current generates heat in the cells through internal resistance (I²R losses). As battery temperature rises, the battery management system (BMS) may reduce available power to protect the cells, which can further limit range.
Lower efficiency at extreme state-of-charge. Battery efficiency is highest in the middle of its state-of-charge window (roughly 20–80%). Driving the battery below 20% under high-current load accelerates performance degradation per charge cycle.
Cold weather amplification. In cold temperatures, battery internal resistance increases substantially, compounding the current-draw effects. Towing in cold weather can produce range loss of 60–70% compared to unladen warm-weather driving.
Why Solving This Isn't Just "Bigger Battery in the Truck"
The intuitive response to EV towing range loss is "put a bigger battery in the truck." This is partly true — more battery means more range even when towing — but it is an inefficient solution for several reasons:
First, battery weight is not free. A larger battery adds mass to the tow vehicle, which increases rolling resistance and reduces payload capacity. Second, the battery has to live in the truck — it is always there, even when you're not towing. You're paying for the extra weight 100% of the time to solve a problem that exists maybe 10–20% of the time. Third, the fundamental cause of the range loss — aerodynamic drag from the trailer — is not addressed at all by a bigger truck battery. The trailer is still generating the same drag force, consuming the same energy per mile.
The structural solution is to address the energy source of the system rather than just the truck's share of it: a powered trailer that carries its own energy and drives its own wheels.
Quick Summary
- EV range drops 40–60% when towing a conventional trailer at highway speeds
- Aerodynamic drag from the trailer is the dominant cause at speeds above 55 mph — it scales with v²
- Rolling resistance adds a linear weight-proportional penalty at all speeds
- Grade resistance matters most on sustained climbs; regen on descent recovers 60–75%
- Slowing down meaningfully extends towing range because of the drag-squared relationship
- A bigger truck battery helps but doesn't eliminate the drag; a powered trailer addresses the root cause
The powered trailer addresses the root cause.
Instead of forcing the tow vehicle to pull a dead load, Aslin Power Trailers drives its own wheels — removing the energy burden from the truck entirely. Up to 150 miles of towing range, per model.
Explore the Aslin LineupRelated reading:
→ How Much Range Does an EV Lose When Towing? (Vehicle-by-vehicle data)
→ What Is a Powered Trailer?
→ The Complete Guide to Towing with an Electric Vehicle