Engine Deep Dive: Toyota Tacoma's Atkinson-Cycle V-6

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By Andy Mikonis

In the world of upgraded and redesigned pickup trucks, new vehicles normally do not get a new powertrain at the same time. This was not the case with the redesigned-for-2016 Toyota Tacoma; it received the 2GR-FKS engine — a 24-valve V-6 rated at 278 horsepower and 265 pounds-feet of torque.

Related: Sibling Rivalry: 2018 Toyota Tundra Vs. 2018 Toyota Tacoma

Though new to the Tacoma platform, it wasn't an all-new engine for Toyota. The 2GR-FKS — an Atkinson-cycle engine — is part of an engine family found in a range of other Toyota and Lexus vehicles such as the Toyota Highlander and Sienna, and Lexus GX, RX and LS. Its distinguishing characteristic is the ability of the intake valve to stay open longer than it does in other engines. That causes some of the air/fuel mixture to be pushed back into the intake manifold, allowing the engine to burn less fuel than a normal engine. However, the downside to the Atkinson cycle is that having less fuel in the piston cylinder chamber means the engine provides less power. Atkinson-cycle engines are most often paired with electric motors in hybrid vehicles to make up for the resulting power deficit. Toyota first used a variation of this engine in the 1997 Prius; now the technology is creeping into other non-hybrid vehicles, the most prominent of which is the Toyota Tacoma.

A Special Engine

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Atkinson-cycle engines originated in the 1800s and used complex mechanical linkages to adjust the length of the connecting rods; today it's done with variable valve timing. The 2GR-FKS uses Toyota's variable valve timing-intelligent wide on the intake camshaft. The controllers are actually in the hubs of the cam gears and are actuated by oil pressure through solenoid valves operated by the powertrain control module. The system can change valve timing within a range of 80 degrees. Variable valve timing-intelligent on the exhaust camshaft changes valve timing as much as 51 degrees. During cold startups, the intake valve defaults to an intermediate position, while the exhaust valve is advanced. During partial-load Atkinson operation, both valves are retarded. As the engine transitions to higher load, the intake valve timing is fully advanced and the exhaust stays retarded.

Fuel Injection

The Tacoma engine uses a fuel system called D-4S, shorthand for direct-injection four-stroke gasoline engine Superior version, which employs both direct- and port-fuel injection depending on need and load. During a cold start, the port injection is initially activated, then the direct injection phases in, delivering fuel during the end of the compression stroke. This allows the ignition timing to be retarded and the exhaust gas temperature raised for a faster warm up. As you may know, cold starts are typically when engines have the highest amount of emissions. Under light to medium loads, a varying combination of port and direct injection is used to provide the strongest, smoothest amount of power. Generally speaking, direct injection is used for high engine load ranges because of its cooling effect on the intake air, which in turn increases efficiency and reduces engine knocks.

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There are a few other features of the Atkinson-cycle engine that stand out. Even though it's not a conventional truck engine, it offers durability that truck owners appreciate. The exhaust manifolds and pipes on the 3.5-liter are stainless steel, and it uses a timing chain instead of a belt for less stretch. Additionally, the piston oil jets have a check valve to keep oil pressure from dropping when the oil level is low. Head gaskets are steel-reinforced as well.

It's also a lighter engine since the block, heads, oil pan and intake manifold are all made from aluminum, and it has composite resin head covers. Additionally, the timing chain cover is integrated with oil and cooling passages to save space and weight. Much of the exhaust system is made from lightweight stainless steel as well.

In terms of maintenance, the Tacoma V-6 comes with coolant that doesn't have to be changed until 100,000 miles; after that it must be changed at 50,000-mile increments. It also uses a serpentine belt with an automatic tensioner.

Fuel Economy

We've spent some time driving V-6 Tacomas with a 4x4 drivetrain. How does it compare with other mid-size V-6 4x4s (or all-wheel drive) with automatic transmissions in terms of EPA ratings? The 2019 Tacoma achieves an EPA rating of 18/22/20 mpg city/highway combined while the 2019 Chevrolet Colorado gets 17/24/19 and the 2019 Honda Ridgeline gets 18/25/21, putting them all in the same fuel-economy ballpark. The Tacoma bests the Colorado by 1 mpg combined but falls 2 mpg combined behind the Ridgeline. It does better across the board than the previous-generation 2015 Tacoma with the 4.0-liter V-6 and five-speed automatic, which rated 16/21/18.

We can look at PickupTrucks.com 2015 and 2016 mid-size truck Challenges for further analysis of the difference the Atkinson-cycle engine makes for the Tacoma. Even though the contests took place at different times and in locations, the testing was consistent enough to make comparisons. During fuel-economy testing, the 2015 Tacoma achieved 17.33 mpg combined empty and in 2016 it hit 19.5 for an improvement of 2.17 mpg. When loaded, the 2015 Tacoma attained 17.12 mpg combined while the 2016 got 20.8 for a 3.68 mpg increase. The 2016 model also bested the test group when loaded, but empty it came in fourth out of five competitors.

Our judges were not enthusiastic about the 2016 Tacoma's acceleration performance during that Challenge. Despite higher factory horsepower ratings, the numbers clocked against the previous generation (same driver) bore this out. The results were a wash. The 2015 got 8.44 seconds in the empty zero-to-60-mph test and 9.97 seconds in the loaded test; the 2016 took 8.59 seconds to hit 60 mph empty and 10.60 seconds loaded — so slower for both runs. The 2015 did the quarter-mile in 16.67 seconds @ 84.0 mph while empty and 17.65 seconds @ 79.5 mph loaded. The 2016 bested it empty with 16.5 seconds @ 88.1 mph and but fell behind at 17.8 seconds @ 82.5 3 mph loaded.

Final Thoughts

So, the Atkinson-cycle V-6 in the current-generation Tacoma made the mid-size pickup more competitive and solidly improved its fuel economy. The gains are subtle, but with stricter mileage and emissions requirements coming in 2025, fuel-saving technologies are likely to become more prevalent in upgraded or redesigned pickups. No doubt Toyota will have something else up its sleeve when the next-gen Tacoma and/or powertrain debuts.

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Cars.com photos by Christian Lantry; manufacturer images

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Comments

Toyota has always been a more liberal based company.

The Atkinson design has proved its mettle in hybrids, where its strengths and weaknesses seem to balance a bit with the integration of the torque from the electric motors. That said, the Atkinson engine minus the boost from electric motors gives drivers a feeling of lousy throttle response. Combine the soft pedal feel with an iffy benefit in fuel economy and you have a result that most reviewers (and consumers) are underwhelmed by. In short, it has not been Toyota's best move.

Ford had a better idea---reduce weight. Better use of aluminum and high strenth steel is the answer. The other car makers know this stuff as well.

The guys in the aircraft industry have been pounding on these ideas for the last 80 years. Lightweight construction, fuel injection and disc brakes all got their start in aircraft. Speaking of disc brakes, Toyota really needs to lose those rear drums.

@Mike Sweers,
This engine is garbage and the reason I didn't get a 3rd gen Tacoma. It is subpar in comparison to competitors power outputs. What a joke Toyota has become in the past decade, way to go Mike.

It seems Toyota has gone lightweight on one of the truck's heaviest components, the engine. Reading this article and discovering the engine itself is almost pure aluminum with a stainless-steel exhaust system means a good 40%-50% weight loss in the engine and bringing it towards a more road-worthy 40/60 weight balance when unloaded. Of course, this means that the shift will go rearward when loaded and a load-leveling hitch is almost mandatory when towing.

I do agree with Papajim about one thing, though; when I press on the gas pedal, I want to feel the truck can get out of its own way. Reducing power under light loads is good for cruising, but in today's driving environment, when you accelerate away from a stop sign or light, you need to step out; a laggy acceleration can get the driver into a lot of trouble and cause impatient drivers behind them to make aggressive maneuvers which could result in crashes. Such slow acceleration is why I sold my '97 Ranger and bought something much, much newer with a stronger engine under the hood.

I can't help but wonder why hasn't one of the the big 3 auto manufacturers, (Toyota, VW group and GM) not brought camless engine technology to production. This is the one remaining internal combustion technology that would be able rival electric motors in terms of power and efficiency. Plus, camless engines will remove a great deal of internal mass, friction and wear items such as cams, lifters timing chains possibly extending oil change intervals. The, list of benefits of applying this technology to ICE's are extensive.

My problem with the motor is how it has no low end grunt. When I step on a truck I want that seat in the pants jerk. This thing just doesnt have it. And performance wise it's a full second behind the gm twins and 1/2 sec behind new Ranger

@Vulpine

The use of alloy in the engine (block/heads) has been around quite a while, even for Toyota. An inline Four can utilize an alloy block and still be very stiff---which is a good thing. Strong and light don't have to be in opposition.

Also agree regarding throttle response and safety. Good point.

Regarding your 97 Ranger, I had a 94 Ranger XLT reg cab/short bed and it was very sporty with its 5-speed manual and responsive steering. Yours may have needed some tuning.

Mine was quick, (and not modified) and lived past the 250,000 mile mark long after the body was shot (accident damage).

We all know one thing! That it and the GM mids get better MPGs then that junk Ford is putting out and lied about LMBO!!!!!!!!

Ok, per article it is a car engine in a "truck" hince lack of torque and hp at low rpm.

then this
"The Atkinson-cycle V-6 in the current-generation Tacoma made the mid-size pickup more competitive "
. How bad was it before this motor came out? Per Motor Trend among the Ridgeline, Ranger, Colorado/Canyon the Tacoma is the slowest at 0 to 60 and quarter mile speeds.

Not just the tacoma that has a aluminum block. The tundra also has aluminum block. I don't think being aluminum has anything to do with it being weak. It's a engine designed for a car that is stuffed into a truck.

@uh huh

engineers are required to consider the engine block's torsional rigidity in calculating the design of the entire engine. There are alloy engine blocks that have great torsional stiffness. The guys who run alloy engine blocks in sprint car racing are a great example of crazy torque in a very light block.

@ reality check

Well a GM small block will set u in your seat and I have one with over 300k miles on it. I'd say that reliable

And the 3.5L is a gutless dog! If its gettinv beat by over a second by its competitors. That's sad!

I can't help but wonder why hasn't one of the the big 3 auto manufacturers, (Toyota, VW group and GM) not brought camless engine technology to production.

-- The only way to go cam-less is to either go turbine or electric; no other ICE completely eliminates cam action one way or another. Since turbine has its own issues with a hot exhaust and no effective way to scrub that exhaust within the size and length of a car's underbody, they would emit more pollutants by far than going electric.

And electric has the advantage of MASSIVE available torque, depending on the size of the motor(s) used.

Aircraft been pushing light weight:

And lets not forget about aerodynamics front ends too, which even some of the midsizers are not. Not to mention full-sizers. Ok, the full sizer 1500s, 150s have the excuse they need more air cooling to come in, but RAM is leading with aero.

Further, the P51 fighter doesn't hold a 4-pass speed record, in propeller craft category, averaging ~535mph, because it wasn't aero. Take a look at that 4-valve per cylinder valve train when you get a chance. For 1940's tech, that was and still is a thing of absolute beauty!

Oh, and lets not forget that the military aircraft industry was the catalyst for turbo technology all because there is 1/2 the air pressure at 18000' compared with sea level.

"Regarding your 97 Ranger, I had a 94 Ranger XLT reg cab/short bed and it was very sporty with its 5-speed manual and responsive steering. Yours may have needed some tuning.
Mine was quick, (and not modified) and lived past the 250,000 mile mark long after the body was shot (accident damage)."
---- Posted by: papajim

Which engine, PJ? How many horses?

Mine had the 2.3L dual-ignition at 112 horses and while it was fun to drive, I had to wind it up TIGHT to get any acceleration. And when outside temperatures rose above 90°F, it lost half that horsepower once warmed up. Cold engine it was ok, hot engine, forget it. She would have been much better with the V6 under the hood.

And that was AFTER tuning and replacing the mechanical fan with an electric one.

Mine had the old Lima 2.3 aka the Pinto engine. Cast iron block alloy heads & twin spark plug heads. They had 2 valves per cylinder and a single overhead camshaft. Same as yours.

With all due respect mine had a ton of power for such a small truck. They were very popular for small race cars in the SCCA

@angleo

We keep having to review this---aerodynamics

Aero is a small part of the discussion because aero is irrelevant at speeds under about 50mph. Idling at a traffic light, for example. Pulling away from a dead stop is where light vehicle weight is so important. Aero is a waste of time, unless you spend all your time on the Interstate 75 or 80pmh.

@Papa WRONG
WRONG WRONG WRONG.

@ Vulpine: http://www.freevalve.com/technology/freevalve-technology/

Re. Way to go Mike.

He's selling every Tacoma he can make, maybe they throw $500 on the hood as a Goodwill gesture.

Way to go indeed.

2019 Chevy Silverado versus Winter: Investigating a Cold Start Issue in the New Silverado (Video)

https://www.tfltruck.com/2019/02/2019-chevy-silverado-winter-cold-start-video/

It’s so ugly, the gremlins don’t know what to do.

"During fuel-economy testing, empty the 2016 hit 19.5 mpg. When loaded, the 2016 got 20.8 mpg. The 2016 model also bested the test group when loaded, but empty it came in fourth out of five competitors."

So a loaded 2016 Tacoma gets 1.3 mpg better than an empty Tacoma? I guess I'll just haul my atv around. This is not the first anomaly in your testing I've seen. It defies common logic and is clearly an indication to how much stock your testing SHOULD hold.

@toyo

all of the magazines do the FE testing wrong.

If you aren't doing your test fill-ups using measured fuel jugs your accuracy is out the window. Must measure fuel. Retail gas pumps are not accurate enough for short-miles testing.

If your test is less than 1000 or 2000 miles the amount of fuel and other variables are too big to eliminate. I've realized this for years but the various magazines just want to publish the story and get on to the next one.

oxi couldn't be here.

But he told me tell you that if you criticize this engine you are a liberal!!!!

oxi does not comment on this V6 engine because I do not have one. I have two Tacoma's both with the reliable 2.7.

Toyota trucks have been having frame rust corrosion for well over a decade. It is an issue they are well aware of. Toyota set up a customer support program to specifically for this. The warranty coverage for frame rust corrosion perforation is nothing but an attempt to cover up an inferior product. My truck still looks brand new but has been declared unsafe to drive due a frame that has rusted out. This is after I was contacted by Toyota about the issue. Toyota said the frame was good and put a “protective “ coating on it. 5 years later it’s junk. Toyota was very polite in telling me it’s my problem. I won’t be buying Toyota products anymore. You can verify my same issue by looking up ‘Toyota truck frame rust’. Toyota may have fixed the issue by now but I’m sure something else will pop up that they will just put a band-aid on and leave you with junk.

Beware!!! Majority of 2012 Tacomas have defective air injection valve and pump assembly. The manufacturing defect allows moisture into these units and disables your vehicle! Toyota initiated a recall for these items in Tundras but has not done so with the Tacomas. It may have been covered under the warranty (64,000 miles on the truck) except Toyota hides behind the "water intrusion" exclusion to avoid honoring the warranty. Now wait for it... The cost to replace these parts is over $2,000. Understandably we were shocked. We were advised by the service manager at our Erie Pa. dealership to contact Toyota directly since we have owned 9 Toyotas over 2 decades. He felt they may reimburse us at least part of the cost due to customer loyalty. Don't bother contacting the "customer experience" line. No help with the bill. ZERO. The dealership did offer a free oil change and detailing.

After reading other reviews it's clear that I'm one of many thousands. Our 2006 Tacoma suddenly started driving poorly. We took it to the dealer knowing already that we had missed a recall on the frame, and sadly it was shot. We got $500 for a 10-year-old truck with about 110K miles on it. I was real happy with the truck until then, but we won't buy another. At least it didn't kill us.

We all know about the frame issues on the Tacomas and Toyota's refusal to fix them. They applied Corrosion Resistant Compound to my truck in 12/2014. It didn't help, the rust is still there and getting worse. Toyota is refusing to do anything more. Class Action Lawsuit in process. Contact Philip **. Attorney is in Arkansas but his name and law office appears in many posts. Spoke with him today and they are looking for more people to join.

2007 Toyota Tacoma V6 4WD TRD - The rear spring broke and when I dropped off the truck to the dealership, they found the frame dangerously corroded. The truck has been in the shop for 7 MONTHS! It is essentially worthless now. NEVER AGAIN TOYOTA!

Started noticing major scaling on the frame in 2011, called Toyota and were told nothing can be done because no recalls were issued. We looked into getting the frame coated to help protect it and we were told it wasn't worth it because it would just continue to rust thru. In 2014 our muffler system went due to the defective material from the frame. Had to put out $700 to replace that. Our mechanic told us it was very important that we contact Toyota and make them aware as to how bad the frame was. I called corporate Toyota and they told me to call the dealership. I call the dealership speaking with the VP of communications, told me to call corporate. I called, emailed, took pictures, even put the pictures on Toyota’s Facebook page and was told call the dealership. After all the run around the dealership (VP of Communications) refused to see our truck saying there was nothing they could do because there was no recalls at this time.

I have a Tundra and was loaned a 2018 Tacoma for the day while the Tundra was being serviced. The 3.5 liter in the Tacoma felt so underpowered as to be dangerous in traffic. It may have decent hp and torque on paper or in the lab but felt awful in the real world where it matters.

I've owned six Tacomas including my 2018. Indeed the 3.5 liter engine with the automatic transmission really does suck, especially is you want to drive it in a "normal" manner...putting the transmission in "drive" and simply stepping on the gas pedal. To get satisfactory performance, I have found that I have to put the truck in ECT mode and shift the transmission into S5 (which locks out the second overdrive). Then the truck sort of performs like my earlier 4.0 liter trucks. Souldn't be that way.

Shame! Shame! Shame! on who ever is posting under my name...but I know that my Tacoma suffers from premature clutch wear....symptoms include hesitation before accelerating and jerking during gear shifts. This is a common problem because many Tacoma owners allow the fluid in the master cylinder to get too low, causing air to get into the Tacoma’s hydraulic clutch system. This messes up the pressure applied to the clutch system, leading to premature clutch wear.

The Toyota 3.5 is a dog.
The Atkins cycle is designed for steady-state, to maximize efficiency, not for normal use with a varied RPM. Toyota missed the boat on it because it doesn’t get better fuel economy, produce more useable torque or horsepower, and the throttle response is lacking. If it were paired with a mild hybrid electric motor instead of a torque converter or clutch, it would be far more favorable.

And when outside temperatures rose above 90°F, it lost half that horsepower once warmed up. Cold engine it was ok, hot engine, forget it...Posted by: Vulpine | Feb 25, 2019

My 95 Ranger 4cylinder had factory AC and memory says it had an electric fan, not a traditional fan running off the water pump pulley. Did your 97 have factory AC?

I live in Florida and the only annoying thing about my Ranger in hot weather was the AC compressors had a switch on the compressor clutch that disengaged the compressor at idle. At engine speeds just above idle the clutch engaged and the AC started pumping the cold air. When the engine wasn't fully warmed up that feature was not noticeable.

I'm still convinced your truck had an issue if it was squishy when hot. Mine ran great and I live in the tropics.

Correction:
P51 speed record category:
Stated as Propeller.
Reclarified as Piston Propeller.

Why? Propeller could include Turbine, ie Turboprop, and the P51 never came with a Turbine.

Germane?

@ Posted by: oxi | Feb 25, 2019 8:33:21 PM,

Another fake poster!

"We keep having to review this---aerodynamics

Aero is a small part of the discussion because aero is irrelevant at speeds under about 50mph. Idling at a traffic light, for example. Pulling away from a dead stop is where light vehicle weight is so important. Aero is a waste of time, unless you spend all your time on the Interstate 75 or 80pmh." ---- Posted by: papajim

False statement, pj; Aero starts to take noticeable effect at about 35mph and ramps up logarithmically from there. Essentially, wind resistance doubles with every 10mph to the point that aerodynamics makes a very noticeable difference between 55, 65 and 75mph on your fuel mileage. But worse, it's not just the coefficient of drag you have to concern yourself about, it's also the frontal area, because that CoD is multiplied by the frontal area of the vehicle to calculate total aerodynamic drag. The bigger the face of the vehicle, the more air it has to push aside.

"2019 Chevy Silverado versus Winter: Investigating a Cold Start Issue in the New Silverado (Video)

https://www.tfltruck.com/2019/02/2019-chevy-silverado-winter-cold-start-video/

It’s so ugly, the gremlins don’t know what to do." ---- Posted by: TNTGMC

That one's so obvious that I can only assume (I know) they've developed tunnel vision. It's cold solder joints on the BCM computer. The wave soldering technique is remarkably fast and under 'normal' temperature variations can be quite reliable. However, an outdoor vehicle has to suffer extremes of temperatures that typical wave-soldered circuit boards don't experience. That this issue is showing up so quickly demonstrates a bad batch of boards suffering numerous so-called 'cold solder joints', of which the best repair is to pull the boards and re-heat (and add solder) to the connections on that board.

It's amazing how intermittent problems like that can be solved by just a tiny bit of added solder.

"My 95 Ranger 4cylinder had factory AC and memory says it had an electric fan, not a traditional fan running off the water pump pulley. Did your 97 have factory AC?"
--- Yes. In fact, that factory AC is downright cold. Give it about 15 minutes even under those 90°+ conditions and it could drive you right out of that cab. However, maybe due to the fact that the truck sat garaged for most of its life, the clutch wouldn't release at idle. I installed a manual cut-off switch so that I could disengage the AC when accelerating away from a light or stop sign.

"I'm still convinced your truck had an issue if it was squishy when hot. Mine ran great and I live in the tropics." ---- Posted by: papajim
--- The problem has to do with the mass air sensor. I did some research and the sensor has a fine wire to detect air temperature in what is to me an screwy manner; when you turn on the ignition, it heats that wire to a certain temperature (measured resistively). If that temperature is not 100° above its starting temperature, it retards the timing, though I forget exactly the purpose for doing so outside of either emissions or economy (I think emissions.) When I first started the engine on a hot day, performance would be "normal." But, let's say I drove 20 miles, park for about an hour, then get back in to drive back home. Because the engine is still hot from the first drive, the return drive was at reduced power, which is why I replaced the mechanical fan with an electric. Unfortunately, the engine temperature was still too warm to have any notable affect on performance after swapping out that fan. The one thing it did do, however, is reduce physical load on the engine by a small amount.

I wasn't willing to spend the bucks for a complete rebuild on an engine barely over 20K miles at the time.

@ Vulpine..I owned a 91 Ranger 2.3 and pulled a fishing boat regularly without.any problems. Occasionally pulled a.double axle utility trailer also without problems.

@vulpine


thanks for the feedback about your Ranger. The Lima 2.3's were good engines and Ford made important upgrades to those engines between the late 1960s and the early 1990s.

RE: Aero

This is not a black/white topic when we're discussion automotive considerations. You correctly note the incremental aspect of it but that's my entire point.

All of that Aero discussion's irrelevant at low-speed (or no speed) situations. My truck spends more time at low speed (and no speed) conditions, so for me whether engineers can make it more efficient at 85mph is much less important than having a truck that will live to see 200k miles click over on the odometer.

San Francisco Bay area has numerous expressways with a 45mph posted. Naïve to think that aero doesn't matters at that speed.

Go run a 26.2 mile marathon with a headwind, ie Boston 2018, or go ride a 100 mile bike ride with wind, and one's naivity to wind, and its' effect, at even those low speeds will be changed forever.

@angelo

Not black & white. Incremental. Varies by degree. Keep repeating. It will become clear.

Chrysler today said it will create nearly 6,500 new jobs as it spends all of that cash (4.5 Billion US) on a new plant, and on adding production capacity to five existing facilities in Michigan.

Also will move 3.6 Pentastar production to Dundee MI and create capacity in Detroit to build a new 3 row Grand Cherokee.

Make America Great in the Future too.

Great news on those FCA jobs in the US! I'm glad people buy US made FCA products, keep those good paying jobs here! I remember seeing a few months back that FCA is working on a new inline 6 for trucks including jeeps etc., that could be another big win for them, to go along with the very nice new Ram design.

@angelo, et al

Aerodynamics matters at all velocities greater than zero, but the extent of impact isn’t consistent, or even lineral with the increase in velocity.

Your running into a headwind analogy actually proves this, opposed to your own point.
You see the Force (F) required to both accelerate and maintain velocity for an object increases with speed. But with wind resistance it enters a near asymptotically increasing curve, as velocity increases. A head-wind is actually simlar to an equal increase in speed.
So, you are walking into a 5 mph head wind at 3 mph, the effective wind resistance, provided a perfectly aligned headwind, is equal to 8 mph speed with zero wind. Now use running. It is significantly more difficult to run into a headwind than it is to walk, and this is because the muscle power required to run into a head wind is beyond the capacity available outside of short bursts.
Such it is for wind resistance at low speeds. Many things have a small effect at low speeds including aerodynamics, rolling resistance, and air flow out of the engine bay.
Actually the most significant contributor to drag is airflow UNDER the vehicle. Cutting air from under the car, while quickly moving it around the car has a 2 fold benefit. 1) much smoother profile at speed and 2) more efficient cooling through better air extraction out of the engine compartment due to lower relative air pressure under the car.

What’s more intriguing is that as the aerodynamic efficiency increases so does instability, necessitating an applied amount of drag to generate downforce. A 3rd gen Elcamino is a good example. With an SS nose cone, and the tailgate down, the 3rd gen becomes unstable at speed. The quarters and sail panels allow the airflow around the vehicle to cause a low pressure, high velocity tunnel off the back. Why put the license plate in the tailgate? To discourage the practice of driving with the gate down. I had one, with 250 lbs of tube sand over the axle between the wheel wells it was fine, without and the gate down, the rear end was very loose. Gate up, no big deal.

Aero matters. But many other factors matter more at low speeds. On the highway, at speed, it is a MAJOR factor.

@james

Well said.

The cars of the 1960s were especially poor in this regard because these designs were simply not a match for the highways that showing up all over the country.

When I was young the speed limits in most places were 45 or 50 unless you were well outside of town. By the late 1960s there were many highways, even 2 lane roads in my area where the limits might be 65 or 70---most vehicles of that time were simply not well suited to those speeds. Plus there were still a lot of cars from the 1940s and 50s that were still on the roads. Not to mention cars that were not well maintained.

Brakes, shocks and especially tires were awful back then. Most cars still had four wheel drums, shocks were a joke and tires were dreadful. It wasn't until better rubber was developed and radial designs became common that tires began to really improve.

Aero was a consideration, but shocks, tires and brakes---along with sensible speed limits was far more important.



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