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Originally Posted by JamieGeek
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Thus my observational data would suggest that, at some point, aerodynamics affects mpg more than weight (I'd guess that weight matters more during acceleration and deceleration events and wind resistance is a greater affect during steady state highway driving).
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Another thing to consider as well: The F-53 chassis is sold with the 3-valve V-10 and the E-Series chassis (Axis/Vegas) is sold with the 2-valve V-10 (362 vs 305 hp: https://en.wikipedia.org/wiki/Ford_M...gine#2-valve_3).
(Not really trying to argue any point, just adding more information to the discussion.) |
Yes, I'm also not trying to argue either way -- from my perspective it is very objective. It is what it is, based entirely on physics and not what we write about it.
You are correct that at highway speed it's more about aerodynamics than weight. No doubt about that. But there is a secondary effect that can play a major role. The engine size and gearing is often sized in proportion to weight to provide acceptable acceleration and hill-climbing ability. And if the (gasoline) engine ends up too large for the requirement, it will be inefficient when operating at lower power loads.
So what happens when similar-size engines are used in a 11,500-pound motorhome like yours compared to a 23,000-pound larger Class A (6.8-liter V10s with 2 vs 3 valves vary by about 10% in power but even less in brake specific fuel consumption)?
It's a safe bet that your Axis accelerates and climbs much faster than large F53 Class As, but at slower cruise speeds the engine isn't working as hard, likely making it less efficient than it could be.
If an Axis (particularly cruising at lower speeds) had a 5.0-liter V8 from the F-150, which also has more power, it would likely get higher MPGs. It's just a matter of time for an engine downsize. After 20 years the V10 is getting old.
It wasn't that long ago that vans and motorhomes had 7.5-liter gasoline or 7.3-liter diesel engines, and now some the size of the Axis are powered by 3-liter diesels, and other motorhomes slightly smaller are getting by with 3.6 to 3.7 liter gasoline engines. Personally, I want to see the lines between Class As and Bs blurred to a greater degree. The Axis is a great first step.
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