Roadmap
A test programme is only as credible as its willingness to say which category a claim belongs in. This page is the register: everything this project has established, everything currently under test, and everything that remains a proposal with no measurement behind it.
The categories are not a ranking. A proposal is not a weak finding — it is a different kind of thing, and the failure mode this page exists to prevent is one quietly becoming the other.
V2V in-motion energy transfer works and has been quantified. Campaign 1 (July 2026): 3,719 instrumented miles, 74.74 kWh delivered across seven independent legs, 7.70 kWh AC per gallon at the outlet, charging accounting for 3.8% of campaign fuel. Delivery held 5.69–6.06 kW across every leg and ambient condition — no output derate was observed anywhere. Campaign 2 (September 2026) repeated it: 5.85 kW mean delivery, no derate through 93°F, and 5.9% of fuel on the return leg that charged for half its length.
The fuel cost of charging is measured directly. A commanded on/off step on flat I-10 at 62 mph (5 September 2026) put 5.8 kW of delivery at 0.75 gal/hr (band 0.65–0.83; 7.0–9.0 kWh AC per gallon) — a fuel-channel result that never touches the truck’s torque model, and the best-supported number in the programme. In economy terms, about 1 mpg at 62–65 mph. The Campaign 2 return, 278 mi with a 5,150 ft net climb and charging for half the leg, ran 13.0 mpg.
The speed curve is measured. One road, one morning, both directions over the same ground, no charging, canopy down (Salton Sea, 3 September 2026): 18.6 mpg at 50 mph, 17.2 at 55, 15.6 at 60, 14.3 at 65, 12.5 at 70. Running 55 instead of 65 buys 21%; there is no knee in mpg, only in the price of time. Aerodynamics account for 62% of fuel at 62 mph.
The hot-weather fuel cost is electrical, not combustion. On a 95°F leg the entire measurable thermal cost ran through the air-conditioning compressor; sustained enrichment did not occur. The pre-trip hypothesis was not supported and has been withdrawn, and Campaign 2 found no enrichment episode at 93°F either. The truck’s own high-voltage accessory loads are now metered: DC/DC converter 0.62 kW and air-conditioning compressor 1.28 kW, moving-time means.
The transmission was never the constraint. Fluid temperature peaked at 228.9°F across 65.5 towing hours in Campaign 1 and at 220.9°F on the Yarnell Hill climb in Campaign 2, against Ford’s P1783 threshold of 275°F sustained more than 5 s. Charging adds about 2°F at equilibrium.
Detail on V2V AC Energy Transfer, the reconciled table on Specifications, and the per-leg reports under Test Data.
Aerodynamic drag by speed-hold sweep — run, and it returned a bracket, not a number. Two earlier methods had failed for two different reasons, both documented rather than repaired. The bidirectional 50–70 mph ladder ran at dawn on the Salton Sea shore on 3 September. Its fuel-side product, the speed curve above, stands. Its drag-area product does not: the truck’s engine-torque channel — the only truck-side force measurement — responds to load changes at about 80% of truth in the cruise regime, so every drag figure built on it carries ±10%. The programme’s own bracket is 2.35–3.0 m². LightShip’s published combined-system figure, Cd 0.46 on a 5.41 m² silhouette (≈ 2.5 m²), sits inside that bracket and is what the published aero statements now use. A neutral coastdown, or LightShip’s hitch-force channel, would close it.
Trailer base-load characterisation — redesigned before it ran. The planned 20-minute Camp-versus-Storage comparison was struck on paper: the trailer’s 12 V charger cycles on a 3–5 hour period, so a 20-minute window samples one phase of it and returns a coin flip that looks like a measurement. The transit legs also showed the truck’s two inverter channels agreeing at bulk charge but disagreeing by a factor of about 4.7 in the 0.94 kW connected state — so what that state represents is now an open question rather than an attributed answer (see Trailer Load & Thermal). The replacement is a passive after-dark observation, not yet run.
Inverter efficiency and accessory metering — measured in motion. The ProPower inverter’s DC-to-AC ratio at bulk charge is ≈ 0.98 from the Campaign 2 current channel; a conflicting 0.87 bench figure is retired. The DC/DC converter and the air-conditioning compressor are metered on the high-voltage bus. The stationary transfer figure is still carried from third-party published numbers.
TrekDrive TurboAssist. The trailer already carries a motor on its own axle. The proposal is to have it contribute tractive effort during the moments the tow vehicle is working hardest — a grade, a merge, a headwind — so the engine does not have to.
What exists today is manual: a binary on/off driven by a hitch sensor. TurboAssist is the proposed automated, predictive version. It is not a product and this project has not measured it, because there is nothing yet to measure.
The evaluation is worth reading precisely because the current numbers are not flattering — see below.
TrekDrive TurboAssist — and why the honest number is not the headline one
A raw comparison of the trailer’s motor on versus off suggested a 47% reduction in fuel rate. That figure is wrong, and the reason it is wrong is instructive.
The trailer’s drive mode and the truck’s power export are mutually exclusive by interlock — running one necessarily switches off the other. So every measurement of the motor assisting is also a measurement of the inverter not exporting, and a naive comparison credits the entire difference to the motor.
Decomposed properly, the mechanical load transfer is 27.8%, not 47%. And once the trailer’s own battery consumption is priced at the measured recharge cost, the net was negative under every modelled battery-cost basis tested.
It does not mean the concept is dead. It means the value is not raw fuel saving, and any pitch built on that number is built on sand. Where the trailer is charged from a destination rather than from the tow vehicle, the sign of the net flips — so the case rests on battery-neutral operation, not on gallons. The thermal-relief argument once attached to the concept has been dropped: charging’s effect on transmission temperature was measured at about 2°F against 46°F of margin, too small to carry anything.
It also means a trigger built on ambient temperature would miss the point: this project’s worst thermal event occurred at 78.8°F ambient, on a sustained climb at 7,500–8,200 ft. Any assist logic aimed at real thermal load needs an altitude or coolant-temperature term, not an ambient one.
Publishing an unflattering result on one’s own proposal is the point of keeping this register. The full evaluation — including the proposed driver-tunable operating modes — is on the TrekDrive TurboAssist page, where every figure is labelled modelled.
Open questions this project cannot currently answer
- Trailer-side instantaneous draw. No tow-vehicle channel observes it, so the trailer’s own energy accounting stays partly inferred. Campaign 2 bounded it only by endpoint state-of-charge readings taken at stops. This is the single biggest gap in the measurement set.
- Drag area as a number. The programme holds a bracket of 2.35–3.0 m² and uses LightShip’s published Cd 0.46 inside it, because the engine-torque channel under-responds to load by about 20% in cruise. Nothing on this site should be read as the programme’s own measured drag coefficient.
- What the 0.94 kW connected state is. Recorded across six Campaign 1 legs and attributed to house-load support; Campaign 2’s input-current channel does not corroborate the output channel in that state. Held open, not retracted, pending the after-dark observation.
- The thermal ceiling on the charging connector. One temperature-driven stop has been recorded across two instrumented campaigns. One event does not establish a threshold, and this project has stopped implying that it does.
- Whether the trailer’s charger engages from a 120 V source, and at what minimum current — which decides whether a tow vehicle without a 240 V outlet can recover a deeply discharged trailer at all.
- Stationary transfer efficiency on this truck. The in-motion inverter ratio is now measured (≈ 0.98 at bulk charge); the parked figure is still carried from third-party published numbers rather than measured here.
Kept visible rather than deleted, because a register that only accumulates is not a register.
Withdrawn: that reduced charging on hot legs demonstrated an equipment thermal limit. It was operator-commanded engine protection. The correlation was real; the causation was wrong.
Withdrawn: that the connected, low-rate transfer state represented standing overhead. It is energy reaching the trailer at house-load magnitude, and switching it off would move the same load onto the trailer’s pack.
Withdrawn: that a purpose-built generator would beat a parked tow vehicle on fuel per kilowatt-hour. Published figures do not support it; the reasoning assumed a continuous low-load operating mode the hybrid architecture does not use.
Withdrawn: a persistent fuel-trim asymmetry between banks, which did not survive being computed across all thirteen reduced segments.
Withdrawn: the canopy-up aerodynamic penalty (+251 N, −2.32 mpg), which the first revision of this page listed as established. The canopy is a camp configuration, not a towing one; the comparison was retired on 17 August 2026, and no aerodynamic figure for the original bed configuration exists or can be constructed. “Partial canopy lift” is withdrawn as a test point for the same reason.
Withdrawn: the 47% TrekDrive fuel-rate reduction, replaced by the decomposed 27.8% (see § 01), and with it the thermal-relief argument for automated assist — measured at about 2°F and dropped.
Measured results live on V2V AC Energy Transfer and Test Data. The reasoning behind the whole programme is on The Honest Bridge.
If you have questions or comments, please visit the LightShip RV Owners Club on RVForums.com and post them to this topic. I monitor that site regularly and would enjoy your feedback.
