Engineering Explained:Why Tesla's Are Bad at Towing

[ldjessee00]

Originally Posted by aerohead

I just posted the beginning of observations on the Model X tow testing,at bottom of #1 (permalink)

Specifically:
*The taller Ram,and its turbulent wake exposes less of Showstar's forebody to dynamic pressure,an advantage lost on the Model X,but not Cybertruck.

But much like the Tesla Model X, the Cybertruck has a 'fastback body', which will not help as much as the more flat back of an SUV or large pickup truck...

At least I think so, if I am following all those items you are adding to the first post.

[slowmover]

Originally Posted by Hersbird

I hope the reality of towing the current crop of trailers with an EV does lead to some better trailers. There is a lot of things that could be done in manufacturing that really wouldn't add much to the cost or detract much from the function to improve a modern camper.

Just cleaning off the roof would be a start.

No. Not really. The roof is the weakest part of the trailer (difficult work for immeasurable gain). And low-profile AC units are available. Place a fairing behind it. Done.

It’s the ground clearance (floor height), and all edge radiuses curved.

Crosswinds matter. Head-on aero doesn’t (where safety is ALWAYS paramount), as it’s relative to conditions. (Wait one day to travel).

Typical RV’er: In a 10-year lifespan at 5,000-miles per year, a travel trailer is underway but 1,000-hours. Lifetime use will be 4,500 hours. (20-weeks).
Packaging efficiency is close enough to five times as important as FE gains.

For the full-time retiree, reliability and longevity Trump a few MPG. There’s no commute. (Wake up).

A fuel burn for a retiree can be GREATLY reduced by planned use. But this conflicts with EM’er virtue-signaling. The vehicle takes the blame. The point to a RV today is that it’s paid for long before age 65. And then, sell the house.

As with cars, there’s a minimum size for a full-time trailer encountering the edges of high summer heat thru deep cold (where leaving is the result). Thermal mass isn’t available. A full range of clothes for two. Plus adequacy of storage for other supplies and especially food which eliminates weekly shopping. Full-sized beds. Fully-built bath (no, “wet bath”). 35-50/gals water tankage. Etc.

Assume it’s shelter when sick or injured. A visiting nurse or physician suffices. Hotels or hospitals not needed. No abandonment.

A 1965-1979 27-28’ Silver Streak or Streamline fits the bill. A Charger/300 can easily tow it. The right size & design for safety, plus long production and fleet use. Given power, a low fuel burn.

Deduct 40% from EPA Highway estimate (or use the Combined Average). What’s the cents-per-mile change to the Annual Fuel Cost? 5,000-mile average annual vacation travel

Focusing on fuel cost won’t deliver more travel. It’s the length of reliable ownership where economy resides. Same as a car. (Garage both).

Degrading packaging efficiency for some gasoline is really dumb. Liquid fuel is what makes an RV possible. The energy content versus weight won’t be changed to favor of batteries + solar, and neither will initial or long-term expense.

You want something nice, get going on a concrete pad plus 30A, water + sewer.

Where HIGHLY aero is designed from scratch, it’s not a pair of vehicles which can be separated. Custom, each to the other.

One had best decide:

- how many miles
- how many years

to get a handle on custom work. And, then, what percentage reduction of fuel burn will justify custom work.

.

.

[slowmover]

Originally Posted by redpoint5

I used to "rally" my '69 bug, and going down a gravel road and tapping the brakes made the car want to swap ends.



I let off the brake when a light turned green once, and the idle power of the truck in 4x4 mode was enough to spin the tires and go nowhere. Had to put it in low range to get 'er goin'.

Had 2 notable fishtails in that same truck. First time was highway 58 near the lake on a sunny morning. Felt like I spent half a minute countersteering and alternating between heading toward the opposite side guardrail, and the ponds on the right side of the road. Fortunately no traffic at that moment, so I could use both lanes of the road to get under control again. I'd guess I wagged the tail a dozen times before getting straight again.

Second time I thought for sure we were going off a snowy cliff. Attempted to slow well ahead of the corner, but that sent the truck into a fishtail and I wasn't getting anywhere trying to wrangle control despite not using the brakes at all. Last second idea, I shifted to N, the rearrend hooked back up, and I made the gentlest steering I could and took the truck to the last couple inches of road to make the corner.

Place trans in Neutral. Steer, only.

.

[Hersbird]

Low profile is still a couple feet of frontal area and there are also all kinds of vents, skylights, TV etc there as well. Just a mini split AC system with the compressor innthe rear in the wake would be nice, or wall mount the A/C with a window style unit contained in a cabinet. That's last one is actually less expensive and how I will do my homebuilt if I ever get to it.

Then like you say, some radius here and there, a little taper wouldn't be that hard, tighten the gap some, etc.

[redpoint5]

I don't see why the RV AC that's used when driving isn't made to be electric from the beginning, and then just utilize that when parked.

If I were to design an RV, it would be a hybrid so that the engine could be downsized to the point that flat freeway cruising is the efficiency sweet-spot, with a battery just large enough to give extra oomph for accelerating and hill climbing, and also to go a day providing electricity to the living quarter. Off the top of my head, perhaps something like a 20 kWh battery. It would be a Prius-like drivetrain to eliminate the transmission with an e-CVT, and ability to recharge the traction battery from the main engine. That also eliminates the need for a genset.

There's got to be a way to cammback the rear and have it still be functional. Perhaps that's where the sleeping platform is positioned. Really though, a bed should fold away when not in use to maximize living space. Probably lots of room for improvement in both space utilization and efficiency in the RV world.

Toyota or Ford, and probably GM too could totally dominate the RV market if they wanted to.

[ldjessee00]

I thought the same thing about RVs in the past, though I was thinking of a bigger battery, minimum Nissan Leaf sized (30kWh+).

I tend to look at the toy hauler versions (has a garage in the back; motorcycle), so I think about how to carry the motorcycle does not need that much vertical space, but would like it once stopped and setup... so instead of slide outs (which I think is a bad idea longevity-wise), how about the back pops up from a sport/camm back end?

When moving on the road, the back is at an angle, providing better aero, but when stopped, the back is 'popped' up and the toy storage has plenty of vertical area to stand up around the motorcycle, etc.

I could also see a living room/bed room being able to be done this way as well, as redpoint5 mentions. (do not need the vertical space when traveling)

[redpoint5]

Originally Posted by ldjessee00

I thought the same thing about RVs in the past, though I was thinking of a bigger battery, minimum Nissan Leaf sized (30kWh+).

I choose 20 kWh based on the Chevy Spark specs. That car has a 19 kWh battery and outputs 140 horsepower.

An RV with an EV supplemental motor that can give 140 horsepower of assistance with a 20 kWh battery can go flat out for about 10 minutes. That would cover most hill climb scenarios I'd think, while minimizing the weight, volume, and expense of a larger battery. Also, any battery 16 kWh or larger qualifies for the full federal tax credit, so the closer to that size you get, the more heavily subsidized the battery becomes. At 20 kWh, it's still a money maker at $375/kWh.

Of course, all this is based on my very limited knowledge of RVs, and assumes one of a certain size that I'm thinking of. They come in all sizes though, so that would necessitate all sizes of hybrid drivetrain. I just think that between eliminating duplicate items like generators and roof mounted AC units, and federal subsidies, adding a hybrid drivetrain could end up costing the same as a non-hybrid while reducing operating costs and pollution.

[freebeard]

Originally Posted by ldjessee00

When moving on the road, the back is at an angle, providing better aero, but when stopped, the back is 'popped' up and the toy storage has plenty of vertical area to stand up around the motorcycle, etc.

This is a teardrop, but could apply to other vehicles.

[ldjessee00]

I have seen this kind of teardrop in person, but I was thinking of something a bit bigger than that.

[freebeard]

The example hinges at the top front, as you suggest. My example hinges at the bottom rear, with a soft top rather than a hard top.