By on February 8, 2012

 

 

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TTAC commentator educatordan writes:

I know this is an exercise in mental masturbation but I find myself thinking about it and perhaps the B&B with their extensive experience could shed some light on the subject.

OK here goes; Will lowering a vehicle improve the vehicle’s fuel economy?  Several manufacturers of lowering systems claim that it will, but would it be measureable?  In my mind even 1 mpg would be significant on certain vehicles.  This question sprung to mind as I was looking at low resale values on fairly clean early to mid 2000s American SUVs.  Those TrailBlazers, Envoys, Raineers, Explorers, Mountaineers, and Aviators are likely as close as were gonna get to a modern version of the all American family wagon and you can buy lowering kits for even the 4wd/AWD versions.  I know lowering a vehicle improves handling a rollover resistance but what about fuel economy?

Sajeev answers:

I hope this isn’t an exercise in mental masturbation, as I sometimes consider this quandary while exiting the freeway in my 1995 Lincoln Mark VIII LSC. That’s because the Mark’s air compressor refills the air springs to raise the ride height 20mm when the car goes below 45 MPH. And, compared to the low-speed ride height, they drive better (variable-assist steering too) and looked pretty cool lowered on the highway…back when they were a common sight on the highway. You may not see a new “Quadra-Lift” Jeep Grand Cherokee perform the same trick, but they do.

Alrighty then! According to this thread, there can be a fuel economy benefit to a lowered vehicle. In theory. Always in theory.

I like the theory of lowering a car to reduce the “frontal footprint” of your tires.  Whether or not lowering the vehicle will mess up downforce to the point of fuel economy detriment is anyone’s guess, unless you have a fluid dynamics lab in your garage. For the purposes of a street car that can be lowered enough to not ruin wheel alignment/suspension travel/load carrying abilities, I suspect lowering a vehicle will improve fuel economy.

 

 

Enough to matter? Maybe not with the massive frontal area of a modern passenger car with zero overhang and nerdy ride heights, but maybe with the long, bullet nose of a Lincoln Mark VIII hugging the ground. Your guess is as good as mine.

Send your queries to sajeev@thetruthaboutcars.com . Spare no details and ask for a speedy resolution if you’re in a hurry.

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42 Comments on “Piston Slap: Raising the Bar by Lowering It?...”


  • avatar
    Rod Panhard

    What about the blog-o-sphere isn’t mental masturbation?

  • avatar
    MrWhopee

    Some cars with adjustable suspension has been known to lower itself at high speed for lower drag resistance, so I suppose this would rang true for tall, bluff-nosed SUV as well. Plus you’ll get added stability and less chance of rollover due to lower CG.

    Just don’t expect miracles.

  • avatar
    redliner

    The last gen Jaguar XJs did this too. In fact, it was possible to catch the system off guard. If you where traveling at high speed, and then came to a sudden stop due to traffic, the system would very noticably increase the right height at all four corners. Unlike some other systems i have experienced, it was not completely unobtrusive, always having a somewhat artificial feel.

    Even if lowering your SUV doesn’t yield a measurable increase in fuel economy, it will improve to handeling.

  • avatar
    Zackman

    Lowering the vehicle will reduce drag a bit, that’s one reason why NASCAR vehicles have effects that virtually miss touching the asphalt by an inch or so.

    The Trailblazer SS is lower than a regular Trailblazer, so there is a (very) slight benefit.

    To get any real noticeable improvement, I suppose you would have to track mileage over a given period of time at varying highway speeds. Whether this makes sense for a “normal” vehicle is anyone’s guess, but obviously someone at Ford thinks so.

    Come to think of it, I’d like to try that on my Impala, as my long commute is mostly highway, at a constant sustained speed. It would be interesting to see the difference, if any, if my car were lowered a bit compared to its normal height. Might be able to break 36 mpg?

    • 0 avatar
      mikey

      @Zackman……If I’ve learned anything from countless vehicles I’ve owned, it would be “if it ain’t broke, don’t fix it”

      The basic platform of your Impala dates back to the mid eighties. Over the years they have tweaked the design,moved air dams,played with gear ratios, fuel delivery and timing.

      36 miles per US Gallon……not bad. As a Canadian I’m a little heavy footed on the highway. Roughly translated, litres, to US gallon,then klms to miles. I’m getting 34 mpg with 09 LTZ 3.9, under ideal conditions.

      Your doing fine.don’t —– with it.

      • 0 avatar
        Zackman

        Hey Mikey!

        No, I’m not fooling with my Impala – I love it too much and when it sleeps in the garage on a winter’s night, it smiles at me in the morning when I start ‘er up for my daily drive!

        I did reach a high of 35.44 mpg back in September. Generally, if I use it only back-and-forth to work, I’ve been averaging 30.5 mpg. Not bad for winter time…

        I sometimes wonder if I should replace it before long, however, but I guess that’ll be a “Piston Slap” question some day.

    • 0 avatar

      Dan, I’m inclined to think there’d be a benefit…but the investment required to lower a car correctly may offset any mileage improvement you’d see.

      The front air dam idea certainly has merit.

      Zackman, you’re pulling down 36 MPG with your W-body!?

  • avatar
    KalapanaBlack

    Now is when I would post a picture of one of those minitrucks slammed so low that the rear wheels come up through the wheelwells in the bed. Think of a Lincoln Aviator lowered that far!

    Might look kinda neat, actually…

  • avatar
    vbofw

    Jeez, that Mark 8 is one good lookin car! Why can’t Lincoln replicate some of that magic? Styling seems to be heading back to that sleek design anyway — in a world of Camcords the only cars that ever catch my attention on the highway anymore are the 4-door coupes. CLS, A7, CC, maybe the next gen Fusion will.

  • avatar
    mikey

    @vbofw…..Off topic,but I couldn’t agree with you more.

  • avatar
    DC Bruce

    As far back as the early frog-nosed Citroen DSs of the late 1950s, it was known that managing airflow underneath the car was an integral part of overall drag reduction. The DS had a hydro-pneumatic suspension which raised and lowered the car and a solid, smooth floorpan underneath. It also had the rear wheels mostly enclosed inside the body. A combination of a low-riding car, a “chin spoiler” and “side skirts” diverts the airflow that ordinarily would pass underneath the car (and get blocked by various suspension and drivetrain bits) and makes it go around the car at speed.

    I’m not sure how well this would work with an SUV, because even a lowered SUV rides pretty high. But, you would have to work the full aero package: chin spoiler and side skirts as well. If you’re seriously concerned about fuel economy and aerodynamic drag, consider that frontal area is the largest contributing factor . . . and SUVs and most crossovers have a big frontal area. That’s why a station wagon of the same weight and carrying capacity gets so much better mileage than a similar SUV — e.g. the original BMW X5 vs. the 5-series wagon. (Neither vehicle had a third row of seats and the X5 actually had less cargo capacity.) The two vehicles had the same engine, althought, with the AWD hardware, the X5 was probably heavier.

    • 0 avatar
      Slow_Joe_Crow

      The GM XFE fuel econmomy package for the Silverado/Sierra pickups does just that. The package includes lowered suspension, a deeper front air dam, a tonneau cover and low rolling resistance tires.

  • avatar
    70Cougar

    Rather than lowering a car to increase fuel economy, try adding a few different colored body panels. This will discourage your wife/children/attractive woman you met at a bar from riding with you, thereby reducing your gvw.

    • 0 avatar
      dts187

      Ha +1

      Around my home town I used to see a slammed S-10 with “Too Low For Fatass Hoes” across the back window.

      The lowered vehicle and concern about total weight show his commitment to better fuel economy. We should all be so green.

  • avatar
    TEXN3

    You’d be better off fabricating a front air dam to move the air around the vehicle instead of under. You’ll notice that alot of CUVs, SUVs, and even pickups have a lower front dam to do so…and improvements are 10-20%. Cheaper and more easily “undone” than lowering a vehicle.

  • avatar
    Downtown Dan

    Common feature on Range Rovers for years. It makes sense to me, though as others have pointed out, the fuel cost saving might not be enough to justify the cost of the conversion. One other thing to watch out for– tire clearance!

  • avatar
    tedward

    Oooh oooh, pick me. I’ve done this before!

    I “experimented” with ride height quite a bit on my last car and I saw repeatable and measurable differences in fuel economy. My results were the obvious…fuel economy was improved when the vehicle was lowered but only if I maintained the factory proportions between front and rear ride height. For a while I was running with worn rear springs (nose high relative to stock) and it hurt fuel economy a bit. Then I was running with stock springs rear and loweing springs front (waiting for replacement parts) and it shredded my economy numbers, absolute murder. Nose pitched down turns the entire windshield/hood/roof into an airbrake/downforce generator.

    Please don’t pile on to call me an idiot for the experiment, it was due to manufacturing defects in suspension components, not a desire to hi-low my ride. On the plus side my fwd sedan (at the time) was a hoot with massive front grip and a “compromised” rear… Who knew a ridiculously front-biased chassis weight distrubtion could lead to any sort of positive benefit?

  • avatar
    TR4

    If you look at vehicles specifically designed for ultra-low fuel consumption (e.g. the Sunraycer) they are not particularly low to the ground. Therefore I would guess there is little or nothing to be gained via this route.

  • avatar
    wstarvingteacher

    I would think that this would decrease the turbulance under the vehicle which is significant. However, you would get lost more bang for your buck by installing panels under the vehicle which would do the same thing and probably do it better. When I searched for aerodynamic improvements that kept popping up. I have some choices to make but that has to be done pretty early. I sincerely doubt that I will alter the handling characteristics of the vehicle by lowering it. Might do the airdam spoiler bit though.

    • 0 avatar
      Educator(of teachers)Dan

      By that logic then skid plates should help fuel economy… :)

      • 0 avatar
        wstarvingteacher

        skid plates are normally under the engine only. They are also heavy. What this is talking about it lightweight and not for off the road vehicles. It wouldn’t last. It is for the whole undercarriage of the vehicle.

        You also will see those covers for the wheelwells as well as smooth wheelcovers. There are many things that probably improve aerodynamics but there seems to be some controversy as to how much. Google something like improve aerodyanmics toyota pickup and you should find the guy from Denton Texas who wored on the aerodynamics of his t-100.

        Guys like you and I who talk about this are not experts. There are some guys tht have done it. Instructables also has some. Just look and you will see.

    • 0 avatar
      bikegoesbaa

      “I sincerely doubt that I will alter the handling characteristics of the vehicle by lowering it.”

      I sincerely *guarantee *you that you will alter the handling characteristics of your vehicle by lowering it.

      You might make it better, you might make it worse, but you will absolutely change it. It would be almost impossible not to.

      • 0 avatar
        wstarvingteacher

        @bikegoesbaa

        I said that badly. Lowering certainly will alter characteristic many ways. Some good, some bad, some tbd.

        I sincerely doubt that I would do that. I know that if I did it would have consequences. I learned that 51 years ago and agree with you.

  • avatar
    Educator(of teachers)Dan

    There’s more at work than just the lowering thing too guys. My fiance is a great woman save one little quirk, she is dead set against station wagons and minivans. The unfortunate bias against wagons (cept the Ford Flex which she adores) comes honest in that she had some very unfortunate experiences in a Custom Cruiser that belonged to her day care provider and constantly smelled of vomit. Most of you know I adore station wagons and my favorite car to date is my 1997 Escort wagon (now being driven by my exwife’s new husband.) My lady does however LOVE SUVS and would be tickled pink if I presented her with a Suburban(!) or her fave of current vehicles the Buick Enclave.

    Since I can’t have my B-body wagon I would so dearly love I’m trying to be subversive. Clean BOF SUVs in the Explorer/TrailBlazer range are going for peanuts. Now I don’t need off-road capability (though 4wd for snowy days would be nice). I guess I’m trying to have my cake and eat it too. I’m not trying to turn an Aviator into a Prius but getting one to pull down Panther/B-body fuel economy would be pretty nice. (FYI lowering kits go for a few hundred bucks and I know a few places I could get one installed.)

    That’s my story and I’m sticking too it.

  • avatar
    texan01

    I lowered my 95 Explorer mainly to reduce the tippy feeling. I dropped it an inch all the way around and it did improve the handling quite a bit.

    As far as fuel economy goes…. it gets 23mpg at 70, and 16mpg at 95. Did that before I lowered it, and still does it years after lowering it.

    For my instance, lowering improved handling immensely but economy-wise didn’t improve.

    • 0 avatar
      Educator(of teachers)Dan

      I’m noticing most of the kits for the 2002-2005 models of Explorer, Aviator, and Mountaineer (first generation with fully independent suspension at all corners) lower the vehicle about 3 inches all the way around. That might make a difference.

      • 0 avatar
        texan01

        that might, I didn’t want to go lower because it’s already close to the bump stops at 1″ and I wanted some semblance of wheel travel.

        The IRS models have more wheel travel than the solid axle models to do. You can lower an older one that low, but it’s on the stops or you have to cut them down.

        The IRS models also have wider tracks than the earlier ones to quell the tippyness.

        I kept the same rake as factory, but now time has lowered the rear even more, but I still didn’t see much in the way of a fuel economy improvment. Best observed mileage was 30.1mpg at a steady 55mph.

  • avatar
    autojim

    It’s anecdotal, but on long highway trips, I got better mileage out of my old Probe GT when I had it loaded with the autocross tires, jack, tools, luggage, etc. than when I made the same trip empty/lightly loaded.

    I also spent a lot of time mucking around professionally with Mark VIIIs back when they were still prototypes and the 20mm lowering job realized a measurable drag benefit at highway speeds, which is why they did it — it was enough that they were able to reduce the drag factor for the EPA fuel economy test dyno rollers on the highway portion.

  • avatar

    I suspect that the smoother the undercarriage is, the less difference lowering will make. If the car’s plastron were as smooth as the carapace, the only thing that would make a difference would be less exposure of the tires to airflow on the lowered car.

  • avatar
    Slow_Joe_Crow

    The GM XFE fuel economy package for the Silverado/Sierra pickups does just that. The package includes lowered suspension, a deeper front air dam, a tonneau cover and low rolling resistance tires.

  • avatar
    TR4

    I see the rationale of covering the tires up to reduce frontal area but consider this: The top of the tire is traveling forward at twice the speed of the vehicle so covering it up should certainly help. The front of the tire is moving forward at the same speed as the vehicle so covering it up with the body could well be a wash. The bottom of the tire is stationary (assuming you are not skidding)so covering it up with the body might actually increase wind resistance.

  • avatar
    don1967

    The shape of the car’s nose must be a factor. I would imagine that a wedge shape which pushes air over the hood is best-suited to lowering, whereas a buck-toothed bumper that swallows air underneath might actually add resistance if lowered… perhaps more than enough to negate any benefit of the reduced tire frontal area.

  • avatar
    MusicMachine

    OMG…every example of one of these still around has the suspension completely blown out.

  • avatar
    flatout05

    I lowered both my previous ride (’98 Explorer) and my current one (’06 Ridgeline). Didn’t do a damned thing for fuel economy. Wish it did, but it didn’t.


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