Will Cars Shrink With New Mileage Rules?


Yesterday's announcement of new fuel mileage and car emissions rules has riled up all kinds of special-interest groups. Some safety advocates suggest that these new rules will lead to smaller cars. The smaller the car, the less safe it is, most experts agree. We've already detailed why, and it comes down to simple physics.

Looking at these new regulations, it is possible that smaller vehicles may be one result of the increased mileage rules. The most radical changes, however, may not impact cars of any size.

The stringent new rules call for an average truck rating of 30 mpg. That means truck-based SUVs especially will see radical changes. For the 2008 model year, Ford's light trucks just beat the CAFE average, coming in at 24.7 mpg. CAFE now is set at 23.1 mpg. Models like the Chevy Suburban and Ford Expedition may become extinct. The Ford Explorer is already moving to a car-based crossover, and GM may have to pull the plug on its slow-selling Chevy Tahoe, GMC Yukon and Cadillac Escalade.

Hummer is in the process of being sold, and its hulking H2 sells so few units a month it's unlikely you've seen a new one in your town in a year or more.

Where does that leave cars? Much safer once there are fewer two-ton SUVs entering the driving pool. Plus, many of the most efficient cars today aren't even the smallest. The Toyota Prius, Toyota Corolla, Honda Civic, Chevy Cobalt, Ford Focus, VW Jetta TDI and Ford Fusion Hybrid are relatively large compacts or midsize vehicles, and they all get similar or better mileage than a Toyota Yaris or Honda Fit. Only the very small Smart ForTwo stands out as something that consumers and safety advocates would consider "too small." Plus, the best-selling cars remain compact and midsize cars.

 It's likely the most fuel-efficient engines in the future will continue to be put into these compact and midsize cars because the cost is more easily absorbed versus entry-level subcompacts.

With another five years before these new rules go into full effect and the resulting new cars and engines are likely to be introduced, it seems much too early to guess at safety ramifications.

Safety could suffer if we boost mileage by making cars smaller (USA Today)  

By David Thomas | May 20, 2009 | Comments (23)


Many car experts have seen my invention to make small cars safer. All have agreed that it can work. All I need is a car company licensing my invention, or $100 Million to design and build my own car.



cars wont shrink in size
they have the tech but dont want to use it right now...dont beleive me, look at europe 300hp in some cars and gets 32 mpg...its possible


no, i dont think that cars will shrink.

in fact, there is no real need to "shrink" them.

technology is advancing, and new improvements are made to engines with each successive redesign (or thats whats supposed to happen). applications such as direct injection, variable valve timing, dual-overhead cams,CVT's, 6-, 7-, and 8-speed automatic transmissions and dual-clutch gearboxes all help improve fuel economy and performance at the same time. the same goes for turbocharging, to an extent, such as VW and Saab's 2.0T engines.these technologies allow larger cars to be pulled around with smaller engines that are more powerful.

the reasons that GM's big three SUV's do so poorly in terms of fuel economy is not necessarily their size, but the engines that propel them. the 5.3L engine in the Tahoe and Yukon only makes 320 hp, a small figure for such large displacement. these pushrod V8's could easily be bumped up in power and efficiency by adding a few minor modifacations such as variable valve timing, DOHC, and direct injection. also, until this year, both of these SUV's used ancient 4-speed automatics.


cars 'shrinking' probably wouldn't be a bad thing. seriously, compare today's compact cars to the mid-sized cars from 10 years ago...they're either the same size or the compacts of today are actually bigger. not sure why the class continuously grew...

as for the truck-based suvs... although many sites love to say that they get horrible fuel economy compared to more efficient unibody suvs, the reality is when you do fair comparisons the fuel economy is about the same.

2wd escape v6/6spd auto 18/26mpg
2wd liberty v6/4spd auto 16/22mpg

that's with the liberty's lower tech sohc v6 and antiquated 4 spd auto. if automakers attempted to keep weight down with the unibody suvs, we'd probably see a greater difference, but it doesn't seem like any are exercising restraint when they design them. most unibody suvs are as heavy as their body-on-frame counterparts.

the real benefit of unibody suvs are that they are more space efficient. they do however give up off-road capability.



I would have to disagree with you on GM's SUVs you mentioned. They get the best MPG of any full size SUV. Take a look on the Land Cruisers or Titans. Both of them use same size or smaller engines with DOHC 4v and get worse mpg than GM's pushrod V8s. Size and weight are the main reasons why trucks get lower MPG than cars. Put the same engine in a smaller, lighter car the MPG will go up. Look at the vette, bigger engine more horsepower more MPG. My 21 year old mustang with a 5.0 easily gets high 20s on the highway, a few times I broke 30. My girlfriend's 08 Scion TC gets a little less mileage on the highway taking simlar trips with an engine 1/2 the size and 1/2 the cylinders. Why? Because it takes X horsepower to move X mass.


the point was that if the automakers introduced these advances to their engines, cars could be getting greater gas mileage regardless of size.

besides, an engine as large as 5.3L making only 320 hp is almost irresponsible.

Audi's V8 makes 350 hp with over a liter less displacement. BMW's makes 360 with .5 less. Hyundai's 4.6L makes 368 hp. Infiniti's 5.0L makes 390 hp; the 3.7L V6 makes 330 hp. Lexus' 4.6L and 5.0L make 380 and 416 hp.

Max Reid

Ever since the gas prices crossed $2 / gallon, vehicle size, weight and power has been shrinking.

SUV's sales have gone down drastically almost down by 60-70 % in the last 5 years.

Whether this rule is passed or not, vehicle size will shrink, thats good thing.

Lets become more energy efficient and cut down our dependence on foreign oil and also save some money.

Reduce weight, reduce weight, reduce weight...



Why are you hung up on the displacement of an engine? I guarantee you those engines you listed do not have as much torque as the 5.3 you mentioned, which is what you want in a big vehicle.

GM's LS series engines are also physically smaller than most if not all the engines you listed and they are not heavier either. Those smaller engines also do not return better mpg in a similar sized vehicle compared to the bigger GM engines.


Shopa, good luck with your invention. I only took a quick skim of some of the documentation and couldn't see the images but it sounds interesting. I hope cars.com allows your post to remain here.

This is all of course assuming you are the proper patent applicant (you know how this internet can be).


JM, you are full of crap. The GM 5.3 engine is one of the smoothest and most advanced V8s on the planet. It shuts off four cylinders under light load conditions, a feature none of the overhead cam V8s offer. If it loses all its coolant it will still get you home using the same cylinder deactivation technology to rotate which cylinders fire without overheating. The 5.3 V8 is not irresponsible - you are for spreading your dung infested comments.


i agree with smokin88lx. many dohc engines sacrifice efficiency for the sake of higher horsepower ratings. gm's ohv engines may not have unnecessarily high horsepower ratings, but they have more than enough torque down low in the rpm range where it's needed, more than enough for the vehicles they are installed in...and they return decent fuel economy.

this was the case with gm's old 3800 ohv v6 too. 'only' 200 hp, but loads of torque and fuel economy over 30mpg in a full-sized impala. it may not have been as smooth as the dohc engines, but it got the job done efficiently.

he also has a point on engine size and weight. dohc engines are much larger and heavier than ohv engines.


"The 5.3 V8 is not irresponsible - you are for spreading your dung infested comments."

Best post yet. I agree w/Smokin88 and Carma. JM, the "technologically advanced", "responsible" examples that you cite to prop your position, are some of the worst performing in their class, fuel economy wise.

X hp to move Y mass (and aero) at Z speed is a fixed ratio. Everything else being equal, lowering engine RPM, friction, and improving combustion efficiency are where it's at. The best way to accomplish that is NOT by adding more camshafts, valves, oil pumps (for VVT, weight, and over all size.

The next big advancements are going to come not from engine development; that low hanging fruit has been picked. Instead, it will come from batteries, and electric motors, and the efficient control of them.

Original sheth


The displacement of the engine only refers to the capacity of its cylinders. It has nothing to do with actual size. Two valve engines almost always make less power per liter than four valve engines. It doesn't mean the OHV engines are not advanced. If you did some research you would know several of GM's OHV engines have VVT. The 5.3L V8 is more efficient than Toyota's 5.7L V8 or Nissan's 5.6L V8. GM also uses AFM management to get better mileage from their truck V8s. AFM cannot be easily adapted to DOHC engines which is one reason why GM is sticking with OHV V8s.

I notice you made no mention of fuel economy ratings when discussing the "irresponsibility" of the 5.3L V8. There are no competing DOHC V8s that get superior mileage. The best mileage of any OHC eequipped pickup is the 2009 F150. Toyota and Nissan's DOHC V8s are at the bottom of the list in fuel economy. The Tundra has considerably more hp but its still not more efficient that GM's trucks with the 6L V8.

Original sheth

The argument that subcompacts will be safer once large BOF SUVs disappear is flawed. Why? Crossovers are heavy. The Buick Enclave weighs 5000lbs while a Fit weighs about 2700lbs. Guess which vehicles will win in a crash? The Edge weighs about 4500lbs as does the Highlander. European crossovers such as the X5, Q7, GL and ML are also very heavy. There are few, if any, midsize crossovers that weigh less than 4300lbs on the road today. Traditional SUVs are even heavier but that doesn't mean subcompacts will fare well once Tahoes and Expeditions start to disappear.


By a bicycle. That's what they do in China.


In response to the comment European cars - i believe they use a higher octane than us in the US. Therefore, their small displacement engines can make the 300hp that was mentioned above.

Regarding the comment that its the engine, not the car - i will have to disagree on that because take Toyota, for instance, the 4cyl in their RAV-4 is the same used in the Camry, but it gets a lower mpg. On the other hand, the V8s used in large sedans get better gas mileage than when used in midsized and large SUVs. So yes, cars will have to shrink.

Finally, in response to the author of this article, yes there will be a lot less new SUVs coming onto the road, but unless the government buys the existing SUVs already on the road, or take they keys away from current SUV owners, there will still be SUVs on the road. How will you be safer in a compact car?

Original sheth

BTW, I am waiting for a list of 300hp gasoline powered cars from Europe that get 32mpg. The BMW 335d only gets 23/33 with 265 and its surely from Europe. And its not selling well either.

no, i dont think that cars will shrink.


Over here in the Netherlands, the Smarts (photo) are pretty common. Unsafe? There are old ladies with grandbabies on bicycles drifting along the side of the busy roads while crazy teenagers speed by in their pimped out Polos and Jettas. Grandma's not wearing a helmet and neither is the baby, nor are all those kids biking to school. What chance does she have in an accident? So driving a Smart doesn't seem all that bad.
I don't see anything wrong with others learning to do more with a little less now.


Actually the big problem with safety isn't SMALL cars, it's cars that are smallER than the other cars on the road. This leads to a tragedy of the commons situation, where it is rational overall to decrease the size of the cars on the road, thus removing kinetic energy from the crashes that happen, but it is individually rational to drive a bigger car than everyone else (thus maximizing your chance of "winning" - at someone else's expense - in a collision).

So I have no idea if these new rules would decrease the average mass of cars on the road (or, even better, reduce the number of vehicles that are much heavier than everyone else's), but if it did, that would actually be an overall win for safety.


It's long overdue that we start looking at roads in addition to cars. Remember, pert near all technology that we take for granted now, including the thruway system, would have seen like fantasy in the past.
Lets create a fantasy again.
We can rework the thruway system to something like a 2-level system, trucks on bottom, small cars on top, we can increase the speed and the safety of both. Fence the top, no flipping off the road.
No accidentally going off the road, I mean. No one will ever stop drivers 'flipping off'.
We can elevate the lower level, give ecology an even break.
Are you asking about money? The government could slip the expenses under the military budget. No one will notice, our foreign relations will be at least as good, probably better, than they are now, and we can put a lot of people to relatively safe work.
Also, it would be a logical continuation to roads that drive cars, like a car wash would.
But that is another dream.

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