Nobody has built this rig yet. Somebody should. The E-Pusher
I’ve been thinking about this for a while and the pieces are all available right now — not in development, not waiting on next-generation battery chemistry, not dependent on technology that doesn’t exist. The Ram 1500 REV proved that a 229 kWh battery pack sitting between frame rails is buildable and capable. The Scout Harvester proved that a naturally aspirated engine acting purely as a generator — never touching the wheels — is the right architecture for range-extended EVs where people want control over when the combustion engine runs. FOX Factory suspension and high-output e-axles are both available off-the-shelf for commercial applications. Solar panels at 22-25% efficiency are on dealer shelves today.
The missing piece isn’t technology. It’s a motorhome manufacturer willing to build on this architecture instead of the 50-year-old diesel pusher formula that the industry keeps incrementally refining. So let me build it on paper, do the actual engineering math, and tell you why this rig would be genuinely transformational for serious RVers.
I’ll call it the Concept E-Pusher. Here’s how it works.
In This Article:
- Why the current diesel pusher architecture is ready to be disrupted
- The battery pack: sizing a 40-foot coach correctly
- The generator: why a V6 makes more sense than a four-cylinder here
- The e-axle drive system and the tag axle active steer case
- Solar on a 40-foot roof — the real math
- The power numbers: torque, horsepower, and why electric torque changes everything
- The drive mode system: how the driver controls when the generator runs
- Real-world range analysis
- What this rig would actually cost and who would build it
Why the Current Diesel Pusher Architecture Is Ready for Disruption
A conventional 40-foot diesel pusher runs a straight-six turbo diesel — Cummins L9, Detroit DD13, or similar — producing 350-600 hp and 1,000-1,950 lb-ft of torque through an Allison automatic transmission to a rear drive axle. It’s a mature, proven architecture with an excellent service network and well-understood maintenance requirements.
It’s also fundamentally a compromised architecture for a motorhome application.
The diesel engine runs at varying RPM depending on road speed and load — it’s least efficient at low speeds and in stop-start traffic, exactly where fuel economy is worst. The transmission introduces mechanical losses. The engine has a cold-start warm-up period where emissions and fuel consumption are elevated. Engine noise and vibration run through the coach structure regardless of sound deadening efforts — every diesel pusher owner knows the hum.
The alternative architecture that the Ram REV and Scout Harvester have validated — a large lithium battery pack powering electric motors at the axles, with a combustion engine acting purely as a generator running at constant optimal RPM — solves all of these problems simultaneously. The generator runs at whatever RPM produces electricity most efficiently, regardless of road speed. The electric motors produce maximum torque from zero RPM. There is no transmission. There is no cold-start penalty. Engine noise becomes a manageable fixed sound rather than a variable drone tied to throttle input.
The engineering case for applying this architecture to a 40-foot luxury coach is straightforward. The execution details are where it gets interesting.
The Battery Pack: Sizing a 40-Foot Coach Correctly
The Ram 1500 REV’s largest battery option is 229 kWh — an extraordinary capacity for a light-duty pickup truck. For a 40-foot motorhome application, we need to think about the battery differently: not just as a driving range asset but as a fully integrated energy management system that handles both propulsion and the entire coach electrical load.
A 40-foot luxury motorhome has a significantly different weight and aerodynamic profile than a Ram 1500. The Ram weighs approximately 7,500 lbs and achieves reasonable aerodynamics. A 40-foot coach weighs 35,000-42,000 lbs loaded and has the aerodynamic profile of a rolling building — a Cd around 0.6-0.7 versus a car’s 0.25-0.35. Energy consumption per mile is fundamentally different.
Working the math:
A 40-foot diesel pusher getting 8 MPG uses approximately 28 kWh of energy equivalent per mile at diesel’s energy density of roughly 37.95 kWh per gallon. Converting that to pure electric propulsion with the efficiency gains from e-drive — conservatively 85% drivetrain efficiency versus the diesel system’s approximately 40% thermal efficiency — the electric version would consume roughly 12-15 kWh per mile of actual road travel at highway speed.
Wait — that’s kWh per mile not per gallon. To be precise: at highway speed a 40-foot EV coach running e-axle drive would consume approximately 1.5-2.2 kWh per mile given the vehicle’s mass and aerodynamics. That’s the honest number. A 229 kWh battery pack at this consumption rate gives approximately 100-150 miles of pure electric range — which is the right target for a coach designed around a range extender generator. You’re not trying to cross the country on battery alone. You’re trying to reach a boondocking site, run the coach on battery overnight, and have the generator available for sustained travel.
The target battery specification for the Concept E-Pusher: 400-500 kWh — roughly double the Ram REV’s largest pack. This is physically achievable in a 40-foot coach where the battery pack sits between the frame rails along the full length of the chassis. The Ram REV fits 229 kWh in a pickup truck frame. A 40-foot motorhome chassis has approximately 2.5-3x the available frame rail length for battery modules, and the coach body sits high enough to clear substantial module depth between the rails.
At 400-500 kWh and 1.5-2.2 kWh per mile consumption, the Concept E-Pusher has a pure EV range of 180-330 miles depending on speed, load, terrain, and whether the AC is running. That’s a genuine day of travel distance on battery alone — sufficient for most driving days between destinations without ever starting the generator.
The coach load — refrigerator, HVAC, lighting, entertainment, water pump — adds approximately 3-8 kWh per day of stationary consumption depending on how aggressively the air conditioning runs. The battery pack handles overnight coach loads without generator use comfortably given the capacity.
The Rear Mounted Generator: Why a V6 Makes More Sense Than a Four-Cylinder Here
The Scout Harvester uses a naturally aspirated four-cylinder producing enough electrical output to extend range in a light-duty SUV. The Ram REV uses a 3.6L Pentastar V6 producing 130 kW of generator output — approximately 174 horsepower dedicated entirely to electricity generation.
For a 40-foot coach application, the four-cylinder is undersized.
Here’s the math:
At highway speed, the Concept E-Pusher’s e-axle system is consuming 1.5-2.2 kWh per mile, or roughly 75-110 kW of continuous electrical demand at 50 mph. A four-cylinder generator producing 80-100 kW of electrical output is essentially break-even — it’s replenishing battery capacity at approximately the same rate the motors are consuming it. That’s fine for extending range, but it means you can never gain battery charge while driving, and any demand spikes — a hill, a headwind, AC compressor cycling — draw down the battery.
A V6 generator in the 3.5-4.0L naturally aspirated range, optimized to run at constant RPM for generator efficiency, produces 130-175 kW of electrical output. At highway speed that exceeds the drivetrain’s consumption rate — you’re actually charging the battery while driving, gaining range over time rather than just maintaining it.
The specific generator specification for the Concept E-Pusher: a 3.6L naturally aspirated V6 — not turbocharged, because constant-RPM generator operation doesn’t benefit from turbo boost and the packaging is simpler without boost plumbing — producing a continuous 140-160 kW of electrical output. Running at optimal RPM for efficiency — approximately 2,500-3,000 RPM for a naturally aspirated V6 in generator mode — this engine runs quieter and smoother than any diesel pusher engine at road speed, and with significantly lower maintenance requirements since it operates at constant conditions rather than variable load.
Fuel tank: 75-100 gallons of regular gasoline. At the generator’s fuel consumption in constant-load mode — approximately 0.4-0.5 gallons per hour — the full tank represents 150-250 hours of generator operation. At highway speed with the generator running continuously, you’re getting equivalent range of approximately 2,000-3,000 miles before refueling, with the battery providing the surge capacity for hills and acceleration demands that the generator can’t meet instantaneously.
The E-Axle Drive System and the Tag Axle Active Steer Case
The primary drive axle on the Concept E-Pusher is a rear e-axle — a single assembly integrating electric motor, reduction gearing, and differential into a unit that bolts to the rear of the chassis where the conventional diesel pusher’s drive axle sits.
Commercial e-axle technology from suppliers like Meritor, Dana, and ZF is available today for applications in this weight class. The Meritor ePowertrain e-axle for transit and coach applications produces up to 350 kW of continuous output and over 24,000 Nm of wheel torque — translating through the rear axle to the road as approximately 3,000-4,000 lb-ft of tractive force. That number makes the most powerful diesel pushers look modest.
Now the tag axle question. Conventional diesel pushers use a tag axle — the third axle behind the drive axle — as a load-bearing passive axle that distributes the coach’s weight over a longer wheelbase for a smoother ride. It’s always been passive: it rolls along and carries weight but contributes nothing to steering or drive.
The Concept E-Pusher spec’s the tag axle with active rear steer — a system where the tag axle wheels turn in coordination with the front steering inputs. Active rear steer at low speeds turns the rear wheels opposite to the fronts, reducing the effective turning radius dramatically. At highway speed it turns the rear wheels with the fronts, improving high-speed stability and lane change response.
For a 40-foot coach this is specifically valuable. The turning radius of a conventional 40-foot pusher makes urban navigation — campground access roads, fuel stations, tight turns — a constant exercise in pre-planning. Active rear steer on the tag axle reduces the turning radius of a 40-foot coach to something closer to a 30-foot coach’s geometry. That’s the difference between fitting into campgrounds that currently exclude coaches of this length and needing a Class A diesel-pusher-approved site.
The tag axle can optionally be electrified as a second drive axle — adding another 200-300 kW of drive capacity for mountain grades and maximum acceleration scenarios. With both axles driven electrically, total system output reaches approximately 500-600 kW continuous — enough to maintain highway speed grades that would cause a conventional diesel pusher to downshift.
Solar on a 40-Foot Roof: The Real Math
A 40-foot coach has approximately 280-320 square feet of usable flat roof area after accounting for air conditioning units, roof vents, antennas, and safety clearances. Using today’s best commercially available N-type TOPCon panels at 22-24% efficiency:
Each 400-watt panel occupies approximately 21 square feet. In 300 square feet of roof space you can fit approximately 14 panels, yielding 5,600 watts — 5.6 kW of installed solar capacity.
In ideal conditions — direct sun, optimal angle, no shading, clean panels — 5.6 kW of solar produces approximately 28-33 kWh per day based on 5-6 peak sun hours in the Southwest. That’s a meaningful contribution to the coach’s stationary load — covering the refrigerator, lighting, entertainment, and communications systems for an entire day without touching the battery or running the generator.
For a boondocking scenario where the coach is stationary for 3-5 days: the 5.6 kW solar array recovers approximately 100-165 kWh over that period, extending the effective stationary range of the 400-500 kWh battery pack by 20-40%. Combined with the battery’s own capacity, a stationary boondocking stay of 5-7 days is achievable without running the generator — assuming no HVAC load. With moderate air conditioning the solar offsets a significant portion of the HVAC draw.
For driving days, the solar contribution is secondary — 5.6 kW against 75-110 kW of drivetrain demand is approximately 5% offset. Meaningful but not transformational on the road. The solar system earns its keep at the campsite, not the highway.
The Power Numbers: What Electric Torque Actually Changes
Here’s where the engineering gets genuinely exciting.
A Cummins L9 diesel producing 450 hp and 1,450 lb-ft is considered a strong diesel pusher engine. Peak torque arrives at 1,400 RPM and falls off significantly above 2,000 RPM. The Allison transmission manages this torque curve through six or seven ratios to keep the engine in its power band across the speed range.
The Concept E-Pusher’s dual e-axle configuration — primary rear e-axle plus electrified tag axle — produces:
- Continuous output: 500-600 kW (670-800 hp)
- Peak output: 800-1,000 kW (1,070-1,340 hp) — available for acceleration and grade climbing, thermally limited to short duration
- Continuous torque at the rear axle: approximately 24,000-28,000 Nm wheel torque, translating to approximately 3,000-3,500 lb-ft at the driveshaft equivalent
- Peak torque: available from 0 RPM — the full torque figure is available the instant you press the accelerator, not after a turbo spools up or an engine reaches its torque peak RPM
The practical consequence of instant torque at 35,000+ lbs: this rig pulls grades that would have a conventional diesel pusher downshifting and slowing. A 6% grade at 65 mph that drops a diesel pusher to 45 mph is managed at highway speed by the Concept E-Pusher drawing on battery reserve for the short duration of the climb. A 10% grade — genuinely challenging terrain for any motorhome — the electric system handles without the labored engine noise, transmission hunting, and speed loss that diesel pusher owners manage through momentum and anticipation.
The other practical consequence: regenerative braking. A 40-foot coach descending a mountain grade in a diesel pusher relies on engine braking, exhaust brakes, and careful brake management. The Concept E-Pusher’s e-axles regenerate electricity during descent — converting the coach’s potential energy into battery charge rather than brake heat. A long downgrade actually improves battery state of charge rather than depleting it. For owners who camp in mountainous terrain, this changes the calculus on energy management significantly.
The Drive Mode System: How the Driver Controls the Generator
This is the feature that makes the Concept E-Pusher genuinely different from just a diesel pusher with better emissions numbers. The driver has direct, meaningful control over the relationship between the generator and the battery — and that control creates use cases that a conventional powertrain can’t accommodate.
Pure EV Mode: Generator off, driving on battery only. Urban environments, campgrounds where generator noise is prohibited, short trips between sites where battery capacity is sufficient. Zero noise from the generator, zero fuel consumption.
Charge Mode (Pre-condition): Generator running at maximum output, charging the battery as fast as the electrical system allows, while the coach is parked or driving. This is the mode you select three hours before arriving at a remote boondocking site — run the generator at the campground with hookups, maximize battery SOC, then arrive at the BLM site with a full 400-500 kWh pack and potentially a week of stationary power available.
Sustain Mode: Generator runs to maintain current battery SOC — matching generation to consumption so battery level stays approximately constant during highway driving. This is the standard long-distance mode — you’re using fuel to cover the driving range while preserving the battery for campsite use.
Efficiency Mode: Generator runs only when battery drops below a threshold — 20%, 30%, whatever the driver sets. Maximizes EV-only driving distance at the cost of allowing the battery to partially deplete before the generator engages. Best for routes with known charging infrastructure at the destination.
Max Power Mode: Both battery and generator output simultaneously feeding the motors — maximum system output for mountain grades, headwinds, or any situation requiring the full 800-1,000 kW peak output. Not a mode you’d leave on for extended periods, but available instantly.
The interface is a simple selection — a dedicated display showing battery SOC, generator status, fuel level, solar input, and projected range under current conditions. Experienced operators develop intuition for pre-conditioning the battery the same way diesel pusher owners manage fuel stops — but with far more flexibility because the pre-conditioning can happen on shore power, solar, or generator rather than requiring a fuel station.
Real-World Range Analysis
Let me run three scenarios with actual numbers.
Scenario 1: Cross-country travel day, 400 miles
Depart with 100% battery — 400-500 kWh available. Highway speed at 65 mph, coach loaded at 38,000 lbs. Consumption approximately 1.8 kWh per mile.
Pure battery range: 220-277 miles before generator engages in Sustain Mode. Generator runs for remaining 123-180 miles consuming approximately 12-15 gallons of gasoline. Arrive at destination with 10-20% battery remaining and 85-88 gallons of fuel. Total fuel consumed: 12-15 gallons for 400 miles of travel — equivalent to approximately 27-33 MPGe. A conventional diesel pusher covering the same 400 miles at 8 MPG uses 50 gallons of diesel.
Scenario 2: Boondocking setup — drive 150 miles, stay 5 days
Depart with 100% battery. Generator stays off — 150 miles at 1.8 kWh per mile = 270 kWh consumed. Arrive with 130-230 kWh remaining — roughly 26-46% SOC.
Solar contributes approximately 28 kWh per day over 5 days = 140 kWh recovered. Daily coach consumption without AC: approximately 5 kWh. With moderate AC: approximately 15-20 kWh.
Without AC: 5 days × 5 kWh = 25 kWh consumed, 140 kWh recovered. Net positive — battery SOC actually increases during the stay. Generator never runs.
With moderate AC: 5 days × 18 kWh = 90 kWh consumed, 140 kWh recovered. Net positive by 50 kWh — still no generator needed.
Scenario 3: Pre-condition for remote site — charge on hookups, drive 80 miles to BLM site, stay 7 days
Depart at 100% battery from hookup site. Drive 80 miles on battery — consume 144 kWh. Arrive with approximately 256-356 kWh remaining. Solar contributes 196 kWh over 7 days. Total available energy: 452-552 kWh for 7 days of camping.
Daily coach consumption with moderate use: 15-20 kWh. 7 days: 105-140 kWh total.
Remaining battery after 7 days: 312-447 kWh — effectively never needed the generator for the entire stay. Drive home 80 miles on battery with 170-300 kWh remaining. Trip completed with zero generator use.
What This Rig Would Actually Cost and Who Would Build It
The honest number: a 40-foot luxury coach built on this architecture, produced at meaningful volume, would price in the $850,000-$1,400,000 range depending on specification. That’s significantly above a conventional diesel pusher in the same length — a 40-foot Newmar or Tiffin diesel pusher runs $450,000-$750,000 — but the premium reflects several hundred thousand dollars of battery pack hardware, the e-axle system, active rear steer, and FOX Factory suspension.
The battery pack alone — 400-500 kWh at current lithium cell costs of approximately $90-120 per kWh at pack level — represents $36,000-$60,000 of hardware. The dual e-axle system at commercial application pricing is approximately $80,000-$120,000. The generator and fuel system: $25,000-$40,000. The solar array: $15,000-$25,000. That’s $156,000-$245,000 of powertrain and energy hardware before the coach body, interior, or chassis.
The company positioned to build this today is not one of the traditional diesel pusher manufacturers. Tiffin, Newmar, Entegra, and Foretravel have neither the EV engineering capability nor the incentive to disrupt their own conventional diesel pusher business. The company positioned to build the Concept E-Pusher is a bus or transit coach manufacturer — Proterra, New Flyer, or BYD Coach — partnering with a luxury motorhome interior specialist. The chassis engineering is bus-industry adjacent, and the battery pack and e-axle technology are proven in transit applications at this weight class.
Alternatively, a well-capitalized startup with the right engineering team could build this from scratch the way Rivian and Scout built electric trucks — but the $1 billion+ investment to develop a new motorhome platform from scratch is a significant barrier.
The market exists. There are buyers who would pay $1,200,000 for this rig. The same buyer spending $650,000 on a 45-foot Prevost coach conversion would find the capability case for the Concept E-Pusher compelling — the torque, the boondocking range, the elimination of generator noise at campsites, and the fundamentally different energy economics are all meaningful upgrades.
What it needs is someone with the engineering conviction to build it.
I’ll be watching from wherever I’ve parked the Holiday Rambler.
Markus Bryant is a full-time RVer and remote mechanical engineer currently traveling toward Vancouver Island in his Holiday Rambler Nautica diesel pusher with his girlfriend and their dog Scout. He covers RV tech, mechanicals, and industry analysis at RV Journal.
