The ultimate efficiency 4-passenger car

[Ernie Rogers]

Originally Posted by Bicycle Bob

So, the Sierra Club thinks that climate change and current trends allow economic predictions more than a decade distant? I wish I found this reassuring.

Hello, Bob,

What is your guess for 10 years hence?

Ernie

[Ernie Rogers]

Hello, Racer,

You have a very good point here. While some of us want a small, simple car, what we are offered is determined by the majority. (My brother-in-law lusts for a Chrysler 300, though he knows the planet is in peril.)

It was about a month ago that Volkswagen announced that they would not be bringing the 2010 Polo Bluemotion to the U.S. because "it isn't big enough for Americans."

Fuel economy claimed for the 2010 Polo is 80 mpg.

Ernie Rogers

Originally Posted by CapriRacer

Consider for the moment that this same question was asked during the 1973 oil embargo, when, interestingly, the price of gasoline quadrupled (Sound familiar?) Cars back then didn't have as standard equipment: Air conditioning, electric windows, cruise control, automatic transmissions, etc.

If vehicles had stayed the same during this entire time, the technological improvments would have resulted in improvements in fuel economy as suggested. However, vehicles that sell today have higher acceleration rates, better crash survivability, less harmful emmissions, more luxurious features, better sound insulation - but they are also heavier. As Ernie pointed out in his article, weight = fuel consumption.

Nope, The problem is you and me and what we are willing to accept.

[Big Dave]

Comments from the Grinch:

1. I do agree that the minimum aspect ratio for an efficient tire is 55% and that might be pushing it.
2. Empirical experience about tire diameter is at variance to the assertion that bigger tires are more efficient. Wheel-tire assemblies are big flywheels that the engine must accelerate along with the vehicle every time the vehicle speeds up. Rotational moment of inertia goes up with the square of diameter. If a vehicle were operated like Class 8 trucks with long periods of operating at more or less constant road speed, this is not much of an issue. Lighter-duty vehicles have to operate in an environment of stop-and-go or at least one of deeper variations in speed. Hence there such vehicles have more scope for having to speed up these “flywheels.” Pickup trucks operate with very large wheel-tire diameters and invariably the bigger the outside diameter, the worse the MPG. I’ve never seen any real world variation in that generalization.
3. The air resistance of bigger diameter tires is subject to debate. With lifted pickups, the air resistance goes up greatly. Maybe, as with the Aptera, sitting taller may get a very streamlined body out of what aeronautical engineers call “ground effect.” Ground effect is the high lift/high drag regime of a wing flying close to the ground. When the plane climbs out of ground effect the rate of climb decreases as lift is lost but air speed increases as drag drops away.
4. High diameter, narrow width “pizza cutter” wheel-tire assemblies have some definite non-efficiency problems. They make the vehicle more top-heavy, therefore for safety’s sake, the designer has to increase track width. “Pizza cutters” are murder on wheel bearings.
5. Moving on to engines, the best way to increase engine efficiency without major expense is to eliminate throttling. Throttling imposes high pumping loads on the engine which reduces thermodynamic efficiency. Two ways around the throttling problem. The first is the diesel engine. It modulates power with the fuel injection and always operates at maximum volumetric efficiency. The EPA despises the diesel engine so using one may be problematic in the US. The second way is to use a true series hybrid. The tramming motors operate off the propulsion battery, and the engine only acts to charge the battery. Thus the engine can be an “on-off” engine that runs at full throttle when it is operating. The efficiency of this setup will approach that of the diesel but will require extra weight, complexity, and expense.
6. To make a high-MPG car, maybe the best approach is to simply lengthen out a 2F1R tricycle like the HyperRocket. Have four tandem seats rather than two. You wind up with a long, but narrow vehicle. It may be necessary to widen out the track and maybe go to a narrow two-wheel rear axle. This longer vehicle will be easier to achieve a very low Cd with. A tandem arrangement vehicle will probably encounter stiff sales resistance from families with small children. You would have to stop the car to tend to the kids. Myself, I’d see that as a feature rather than a bug. (I nearly met my Maker one night when some tom-fool woman reached over to mess with the brat and swerved in front of me) People with kids probably will not see it that way.
7. The four-seat car is a necessity and may become more so. If people cannot afford but one car, it has to meet the family mission. As cars become more complex and made of exotic materials, they will become more costly. Higher price means lower volume. So the four-seat car is not going to go away.
8. As I stated before, you can mandate all you like, but the car has to be designed to meet the needs of the customer at a reasonable price or they simply will not buy it and view whatever agency that foisted an unacceptable car on them as a latter-day version of Jimmy Carter’s sweater.

[Bicycle Bob]

[QUOTE=Big Dave;104375]Comments from the Grinch:

2. Empirical experience about tire diameter is at variance to the assertion that bigger tires are more efficient. Wheel-tire assemblies are big flywheels that the engine must accelerate along with the vehicle every time the vehicle speeds up. Rotational moment of inertia goes up with the square of diameter.

Aye, but wheel RPM for a given speed decreases with greater diameter. The tread moves at the same speed, there's just more of it.

3. The air resistance of bigger diameter tires is subject to debate. With lifted pickups, the air resistance goes up greatly. Maybe, as with the Aptera, sitting taller may get a very streamlined body out of what aeronautical engineers call “ground effect.” Ground effect is the high lift/high drag regime of a wing flying close to the ground. When the plane climbs out of ground effect the rate of climb decreases as lift is lost but air speed increases as drag drops away.

Aircraft in ground effect have less induced drag. The ground makes the wing more efficient; it does not affect form or skin drag substantially.

4. High diameter, narrow width “pizza cutter” wheel-tire assemblies have some definite non-efficiency problems. They make the vehicle more top-heavy, therefore for safety’s sake, the designer has to increase track width. “Pizza cutters” are murder on wheel bearings.

Or the designer can adjust the suspension and bearing sizes to suit. Given the wheel offsets that don't seem to demand bearing changes, and the more constant loading they induce, I'd not worry about that.

[Bicycle Bob]

Originally Posted by Ernie Rogers

Hello, Bob,

What is your guess for 10 years hence?

Ernie

If any of the company names seem familiar, it will because the new operators are leaving them as local landmarks and history. International trade will be much reduced, and there will be either far fewer domestic animals, or people. Most technology will be makeshift, locally adapted and recycled. Unless a world government is collecting taxes for effective carbon sequestration, agriculture will be failing. We might also be recovering from nuclear war, loss of the grid to a solar storm, or other earth changes.

[dcb]

Originally Posted by Big Dave

6. To make a high-MPG car, maybe the best approach is to simply lengthen out a 2F1R tricycle like the HyperRocket....and maybe go to a narrow two-wheel rear axle.

Doh! ya went the wrong way with the number of wheels and at the wrong end too You are absolutely right though that narrower is better efficiency wise.

It isn't much of a stretch to envision a drive by wire two wheeler that is as easy to drive as a 4 wheeler, with auto outriggers or some other stabilization scheme thing you and I arent yet clever enough to describe.

Do like the commuter trains and have the seat backs be moveable so you can have people facing each other. Heck drive by wire from any (preferrably forward facing) seat for that matter. Just don't get so attached to the crutches of extra wheels, or worse yet, mandate them.

And of course being narrower it will collide with less stuff besides air.

The pizza cutters on my 10 speed never had a problem with the bearings

[RobertSmalls]

Originally Posted by Ernie Rogers

Uhh, the Aptera is an EV?

I guess I was thinking about the Aptera 2h.

Originally Posted by dcb

The pizza cutters on my 10 speed never had a problem with the bearings

That's because you incline the vehicle when you turn, so there's little axial load on the bearings.

If your design leads to bearing problems, there are solutions, such as bearings wider than the wheels, or a 30kmi wheel bearing replacement interval. Or by inclining the vehicle when you turn: General Motors (GM)

[dcb]

Originally Posted by RobertSmalls

That's because you incline the vehicle when you turn

Of course, "real" vehicles lean into corners, better visibility when upright, better handling in the corners, less scrubbing. not like all those ox-carts you see on the roads these days

[jamesqf]

Originally Posted by Ernie Rogers

James, your problem is simple-- you are smarter than the average U.S. car buyer...

You know, Ernie, most of the time I don't actually regard this as a problem :-)

[jamesqf]

Originally Posted by dcb

Of course, "real" vehicles lean into corners...

Which can make life rather... um, interesting, shall we say? in the winter, when there's a bit of snow & ice around. Or loose gravel, any time of year.