DIY Electric Car Forums banner
1 - 2 of 16 Posts

· Registered
8,639 Posts
F450 is only rated to ~14,000lb GVWR, iirc. The engines in them were 235HP 7.2L diesels. That's 300kW full power up a steep grade, say 6%, at 60mph.
It's apparently an E-450 (E-Series (formerly Econoline) van cutaway), not an F-450 (SuperDuty chassis-cab). Still, the model numbering corresponds roughly to the truck GVW classification and the E-450 barely makes it into the implied class (4) so about 14,500 pounds is right (the GCWR is much higher, so it belongs in the class) and it's roughly comparable in weight to an F-450.

The E-450 has come with various engines, in the last generation covering just about every engine found in medium-duty trucks. Yes, 235 HP would be common, but that's 175 kW (not 300 kW).

That increase in grade requires about 840 pounds of force, assuming Ford didn't design for gross towing weight. Assume 30" tires...about 1000ft lb. Back that into a 4.56 rear end ratio, direct drive turns ratio is 219 ft lb. Guess it at 2500 RPM gets us 104HP or about 130kW.

Backing that out of the 300kW leaves us with 170kW used at 60MPH if we assume Ford designd the e/f-450 to climb a 6% grade at highway speed at rated GVW.
Aside from the erroneous value of 300 kW, I see no reason to assume that any vehicle manufacturer would assume a requirement to maintain 60 MPH up a 6% grade at GVWR. Drive in any mountain area, and you'll find lots of trucks working all-out to maintain much lower speeds up the grades.

An easier way to calculate the power required to climb is to look at the rate of change of potential energy. Energy due to height is the product of weight and height. 60 miles per hour is one mile (5280 feet) per minute or 5280/60 = 88 ft/s; 6% of that multiplied by 14,500 pounds is 76560 lb-ft/s. One horsepower is 550 lb-ft/s, so that's 139 HP, or 104 kW. It's easier (no weird factors to remember) in metric units.

Tire size and axle ratio matter to what combination of torque and speed is needed to drive the shaft, but not the power required.

If the guess of 1 kWh/mile is correct for the energy needed to keep moving against aero and rolling drag, that's 60 kW at one mile per minute, or 164 kW to maintain 60 MPH up a 6% grade... coincidentally about the peak rating the of the example engine.

· Registered
8,639 Posts
One thing I’m also confused about is GVWR vs curb weight. My understanding is GVWR is the maximum allowable weight, including passengers, cargo, and tow. The curb weight is full tank of gas, no driver or cargo. Hard to find the actual weight without a trip to the dump.
Close, and maybe correct depending on whose terminology you use...
  • Curb weight is with full tank of gas, no driver or cargo (or trailer)
  • Gross Vehicle Weight Rating (GVWR) is the maximum allowable weight, including passengers, cargo
  • Gross Combination Weight Rating (GCWR) is the maximum allowable weight, including passengers, cargo, and anything towed
In some commercial truck contexts, GCWR is referred to as GVWR and no separate GVWR is considered. For an E-450, about 14,000 pounds is the GVWR, not GCWR (resulting from front and rear axle load ratings - GAWR - of about 5,000 and 9,000 pounds).

Actual weight is easy because there are lots of scales. Yes, you can use a dump, or a commercial truck scale (where they charge for an accurate vehicle weight), or highways scales used for commercial vehicle enforcement (and in some areas freely available for any vehicle).

Also consider the 1,500lbs of engine, transmission, and fuel would not be present, not to mention the 15-20 passengers weighing ~3,000lbs it is designed to carry, and the foldaway bench seats weighing ~400lbs.
I don’t have a ton of stuff, but I might have half a ton of stuff say +1,000lbs. Truly guessing here, but I imagine the GVWR includes people’s luggage too, and a bit of flexibility.
The point is, it wouldn’t actually weigh 14,050lbs.
Any conversion to EV of any type or size of vehicle causes a net increase in mass if it has significant range, due to the required battery size.

Conversion from passenger to RV service (which is the goal, I assume) is unlikely to decrease empty weight, but the stuff you carry in it may be lighter than a full load of passengers and luggage. Due to water (and later waste), RVs routinely operate near GVWR, including Class C motorhome built on the E-450 (which is why they use the E-450 instead of the lighter and less expensive E-350). If you use it as a mobile tent (a big empty box with no cabinets, no appliances, no plumbing) it would be lighter... and pointless.

I think that it is reasonable to plan on the basis of the weight being close to GVWR.

I am new to this, and not confident in making calculations, but for reference, these already exist: Products – Phoenix Motor Cars
Yes, lots of conversion of this vehicle have been done, and the most effective way to get a good conversion is probably to buy a used one, since institutional and commercial operators have been known to buy "green" vehicles for political reasons and quietly retire them a few years later.

And fwiw the tires are 16”, not 30”
The earlier reference to tire size was the overall diameter (which is what is relevant to gearing calculations), not the nominal wheel diameter (which is irrelevant to gearing calculations).

Also, I hope this doesn’t ruffle any feathers, but I would want to use LiFePo4 batteries.
While some EV manufacturers use LiFePO4, most EV manufacturers and most EV conversions do not. I don't see a reason to worry about ruffling feathers.
1 - 2 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.