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Old 12-29-2018, 10:47 AM   #511 (permalink)
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2004 CTD - '04 DODGE RAM 2500 SLT
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Originally Posted by ChopStix View Post
Streamlined 1938 Reo Tractor and Curtiss Aerocar

Not really aero by todays standards....

I’d dispute that.

Granted, that’s a one-off completely custom vehicle. Let’s give it disc brakes and fully independent suspension. And a drivetrain that will allow it to meet the mark on a tow combination: 0-60/mph in from 20 to 30-seconds. An auto transmission. 6, 8 or 10?

I’d bet that Cummins crate motor 2.8L V6 would fit the bill. Turbocharged diesel. As I’d also bet that rig doesn’t weigh much. How much fresh water and propane it carries is a determinant.

By determinant I mean number of nights aboard without re-supply. And let’s posit a temp range of from 50-80F (why do we build for mobility? Chase shirt sleeve weather).

Fuel capacity is right in there with other supplies aboard. I’d figure three nights as a good minimum. Thus 30-gls fuel as complement. 80% range would be 500-miles or better. 250-miles out and then back the same. A geared top speed of maybe 63-65/mph.

But that’s on today’s Interstate. 21-mpg (which i believe low). A 400-mile range on US & State highways where terrain wasn’t punishing.

As to “aero” with an RV: it’s all about crosswinds. Everything about that rig is ideal in that regard.

To call it aero and thus impute high mpg, is correct. But high mpg is relative and also unimportant. To understand why aero matters in an RV (crosswind handling) is to understand that total annual miles is low.

This rig was built to lower HP demand. The engines of the day were so low in compression that hill-climbing was arduous. 12-15/mph wouldn’t be uncommon. A truck (wrecker) might be chained to the front to make the tough ones. This was so right into the 1970s with a motorhome trying to get over a Colorado pass. Recommend you look up HP loss according to altitude. Fuel injection is decent (1985) and turbo reliability in sustained demand (high HP, as with the Cummins) is really circa 1995.

A pair of boxy vehicles wouldn’t likely ever cruise 35-mph in the era. And be handicapped by any grade (where wind gusts aren’t to be tempted).

A saying of aircraft designers right thru the 1950s was, “If it looks right, it probably is” (test confirmation). Will this vehicle stay upright? (Is the first test). Can it cruise at 50-mph plus? I’d imagine it did both. The giveaway and refutation to the objection is GROUND CLEARANCE. Look.

Raising cruise MPG with our 2018 drivetrain (and brakes: that’s key) is only a bonus.

What hurts today’s trailers is that the majority aren’t configured for use by a family vehicle (a Chrysler or Honda minivan). But when it is (Airstream), then highway mpg at 63-mph isn’t really a concern. 16+ certainly with a 23’.

A pair of motivated & skilled drivers over the same trip (hours apart) would show that custom with 2018 drivetrain well ahead of its off the shelf modern equivalent.

Is it aero by today’s standards (which are no better than 1926)? It most certainly is.

A failure in understanding on this forum and on the RV forums is that an empty vehicle doesn’t exist. MPG with driver-only is meaningless. Load vehicle to 80% of payload maximum and then see what is “true” mpg. And do it without cease at least 13-weeks (a full calendar quarter).

Vehicle specification drives all else.

“My XYZ gets 50-mpg!!”

No, it doesn’t.

Moving only yourself and 20-lbs of gear isn’t any test at all. Those are “ferry miles”.

The driving skill curve is arduous (emotional) and not in tune with today’s “adults” (who aren’t, in main) to learn how to use every single HP to best effect. Being slower than all other traffic is a given. How best to glide along smoothly isn’t easy. Not evade safety, but to maximize that practice (separation distance).

A solo vehicle loaded according to its design is the MPG test.

And AVERAGE MPH is the determinant of aero viability. The annual number.

So, having circled back around on “what is aero” THAT is determined by function. A city commuter has little need. All trips are short (under three hours) and UTILITY ranks higher (ease of ingress/egress for passengers, etc).

Relatively, a box versus an egg. A 27-mph annual average box isn’t much different than its egg equivalent. But it’s a whole lot easier to live with every persons age and physical condition. (If one posits, “well, it’s only me” go away. When you’re down to one close living relative as am I , then that MAY apply).

When the spec is for that which will see 35-mph + annual AVERAGE mpg, now “aero” has become predominant.

Is it aero? What’s the spec? (must first be answered).


2004.0 DODGE Ram QC/LB 2500 2WD/NV-5600 305/555 ISB. 7,940-lb. Stock. 200,000 miles/5000-hrs @ 40-mph average.
1990 35' Silver Streak TT 7,900-lb.
11-cpm solo & 19-cpm towing; 21-mpg average past 54k-miles
Sold: 1983 Silver Streak 3411

Last edited by slowmover; 12-29-2018 at 11:11 AM..
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