By on November 3, 2011

When you wish...

TTAC Commentator Seminole 95 writes:

Sajeev,

I enjoyed reading the responses on my NVH question.

Here’s another question for you. How significant is that Honda uses a double wishbone suspension on their family sedan (the Accord) whereas the Toyota Camry, Chevy Impala, and Hyundai Sonata use the cheaper MacPherson strut? Does the DW suspension make handling better in the turns? Does it last longer than a strut suspension, thereby giving you better ride quality as the car ages? Is the DW something that a car buyer should favor, or is it more complicated than that? I remember that many fans complained when Honda switched the Civic from DW to strut.

It looks like the Ford Fusion might use the DW suspension, but I am not sure. Interestingly, it also looks like the BMW 3 series uses a strut suspension, so maybe the DW is not necessary.

Sajeev Answers:

I think BMW signed a Deal with the Devil to make such an enlightened driving experience, as many of their famous machines run such illogical items like steering boxes (not rack and pinions) and the aforementioned MacPherson Strut design. Just kidding.  Except not…the E39 M5 shouldn’t do what it does with such boneheaded bones. And yet it did!  And still does!

Well, then!

Fact is, the suspension design (by itself) isn’t a big issue for most passenger cars. This excludes killer F1-like race vehicles, if you missed that. Odds are there’s more low-hanging fruit in one’s choice of geometry/alignment, spring, shock, sway bar and tire compound than there ever will be in a MacPherson vs. Wishbone quandary.

When it comes to automotive suspensions, I am a big fan of less is more. Which is laughable, considering the multilink design and air bladders in my Lincoln Mark VIII, one of the finest riding/handling cars out there (once you neutral out the handling with Addco sway bars). But my car needed tons of replacement parts after 10+ years and 120,000+ miles, parts which either do not exist or are far cheaper/easier to replace on a normal MacPherson setup. So maybe my point is still valid. Possibly.

I wager this issue is a red herring, the bigger problem is what I mentioned before: spring rates, shock valving and tire quality. Hell, tires are the most important part of this equation! Best and Brightest, off to you!

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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44 Comments on “Piston Slap: Strut ‘yo Stuff or Make A Wish?...”


  • avatar
    Contrarian

    My D2 A8 has eight control arms plus two swaybar links and two tie rod ends that need replacing at every 100k miles or so. As a DIY I can do it for around $450 and a day’s work. The dealer charges around $2000.

    When they are new, it is a wonderful ride. Worth it? For me, yes, since I only DIY.

    • 0 avatar

      I feel you pain…only much, much less so in an MN-12 based Ford.

    • 0 avatar
      Thabo

      Contrarian – Funny thing, after reading this article and having jacked up my D2 A8 just a day ago I wondered if anyone else had ever marveled at the mass of control arms and bushing on these beast! I have has a clunking sound on the rear left of mine when ever I go over a really big pothole since 2006 and have always been too nervous to even have it looked at even though I’ve got a good mechanic. I even took photos of the offending bushing but one day I will need to replace it – got 166k on the beast.

      • 0 avatar
        Contrarian

        Thabo, Here is a secret for you. If you go for replacing all the arms, buy a set for a 2001 A6. The set is much cheaper and only the front uppers are different – and those you can buy by themselves. I just did that and the results are great.

  • avatar
    Darth Lefty

    The auto manufacturers like the strut suspension because it packages better. You get more room for the engine in front and a lower floor in the back when you don’t need to provide upper arm mounts and clearance.

    The WRX hatch switched from strut to wishbone in the rear in 2008, raising the floor. At the same time they made the back window more raked. The loss in cargo room is noticeable, especially to my geriatric dog. She can’t quite jump that high, scrabbling on the paint, and she keeps getting hit in the nose when I close the hatch.

    • 0 avatar
      nikita

      Beat me to it. To an engineer designing a mass-market car, suspension design selection is mostly about packaging. The devil is in the details. I had an e36 BMW with struts that lasted well over 100k miles and a Mk I Ford Fiesta with ones that lasted 18k, replaced by Koni units that outlived the car. My current Honda Fit has a twist beam rear axle and rear drum brakes, while the Camry it replaced had rear disks and muli-link rear suspension. Guess which car is quicker on a mountain or canyon road?

  • avatar
    jpcavanaugh

    It was always my understanding that the double wishbone (or short long arm or A arm) suspensions are preferable because their geometry permits more camber change through the suspensions travel. In other words, as the car leans in the turn, the outside wheel thrusts its lower side out while the inside wheel pulls its lower side in, allowing a better tire contact.

    The struton the other hand, allows much less camber change, so that under hard cornering, the tires are able to plant less firmly.

    Or is this obsolete information? I prefer the non-strut systems for the ease and economy of replacing shocks, and better access in the engine bay (at least the upper half).

    • 0 avatar
      cdotson

      jpcavanaugh, what you say is correct but is also a generalization. For an average daily driver a well-designed strut suspension will perform equally well as a well-designed SLA (short/long arm or double wishbone) suspension. For a track ride, struts just don’t cut it.

      Maybe I’m biased, having dabbled in some SLA suspension design, but I’m firmly in the SLA camp. My experience however has proven to me that a poorly-designed SLA suspension will likely perform WORSE than a poorly-designed strut suspension and it’s probably easier to eff-up an SLA design if the designer doesn’t know what they’re doing.

      The biggest impact that strut vs. SLA has that particularly pertains to emergency handling or track usage is the control of roll center and roll axis locations. Designers just getting into suspension design often make the mistake of assuming that the roll centers and roll axis (the imaginary axis between the front and rear roll centers) always lie on the vehicle’s centerline. They don’t. In a strut suspension it is much easier for the roll center to migrate further from the vehicle’s centerline. It is not difficult at all for the front roll center of a strut setup to migrate to or outside of the outside front tire which can wreak all kinds of havoc on tire wear from overloading.

      The roll center of well-designed SLA setups is much more controlled both laterally and vertically as there are may more design parameters that can be changed to affect the roll center movement. Vertical roll center migration changes the over/under steer tendency of the chassis. A roll axis that is higher in the rear and lower in the front tends toward stable understeer, but the steeper the slope of this line the more pronounced the tendency becomes. The larger the migration of the roll center during hard cornering, the less “predictable” the car is because it’s understeer tendency is constantly changing magnitude.

      Again, little of this matters for average cars for daily use, and all of it assumes that time was spent bothering to whip up a competent design. I’m willing to bet that more often than not the emphasis on the former outweighs the emphasis on the latter.

  • avatar
    psarhjinian

    Sajeev is right on the money.

    Honestly, struts versus DW is mostly fan-forum wankery. Hell, fully-independent versus torsion-beam in a front-driver is similarly wankish (wonkish? both?).

    For a “normal” car most people don’t care, won’t notice, and as Sajeev notes, shocks, springs, sway bars and tires make as much or more of a difference.

    And again, as Sajeev says, this isn’t to say there’s not a good reason for, say, a independent rear suspension versus solid-axle at the rear, or multilink versis struts up-front for different types of high-performance driving, but outside of that even most performance car drivers wouldn’t know/care if you swapped out the Mustang’s rear axle for an IRS.

    Personally, I’m totally fine with struts up front and a torsion bar at the back**. It keeps the price and complexity down and the cargo space up. If you’re less boring than me, you might sing a different tune.

    ** Other things I’m okay with: rear drum brakes, four-speed automatics, conventional fuel injection and hard plastics where your elbows never go. Does the car do what it needs to do well? Yes? If so, then anything else is sophistry.

    • 0 avatar
      carbiz

      Shocking! Absolutely shocking! Heresy, I say! Off with this man’s head for speaking absolute common sense!

    • 0 avatar
      chaparral

      I’m a lot less boring than you on this count, but agree with rear drums, 4-speed autoboxes, and Dacron and plywood rather than carbon fiber. Unequal-length A-arms have a huge advantage on ride and handling over any strut suspension.

      First off, you can get a decent amount of suspension travel in there – bump and droop travel aren’t limited by how high the shocktower top can be. This is the primary limitation of struts in a street car. You either get a wallowing marshmallow that bottoms out all the time or train springs and more suspension movement through compliance than through travel. Typical wheel rates for 2500 lb sporty cars with strut suspension are in the 300-500 lb/in range which isn’t enough to keep them off the bumpstops. With double wishbones, you’re looking at 200-400 lb/in springs with a motion ratio that takes it down to 120-300 lb/in.

      Second, you can design in some camber gain, so the tire can be kept something like flat in roll without a forearm-sized antiroll bar. You also don’t automatically kill the outside edges of your tires trying to drive faster than a meter maid who’s paid by the hour – with struts you choose between that and killing the inside edge of the tires on freeways with static camber.

      Finally, the hoodline can be a lot lower with the double wishbones, as the spring and damper can be mounted to the lower arm rather than starting above the axle line, and the motion ratio also allows you to have a lot less than 1″ of damper travel per inch of bump or droop travel. It’s no accident that old Hondas are fishbowls.

      • 0 avatar
        jhott997

        What?!

      • 0 avatar
        psarhjinian

        Unequal-length A-arms have a huge advantage on ride and handling over any strut suspension

        I don’t disagree on this in absolute terms. I’m positing that it doesn’t matter at the Accord/Camry level where people do drive, well, like meter maids most of the time, the tire and shock/spring choices make as much or more difference, and people would rather the dollars be spent on things that matter more to them.

        To the point about hood height: you’re right, but again this more a stylistic choice than anything else. The current Accord retains the wishbones, and older Camries also used struts. The truth of the matter is that we could have cars with better visibility, only designers like drawing sleek pillboxes on dubs more than they like drawing riffs on the MkI Golf.

      • 0 avatar
        burgersandbeer

        As I understand it, the raised hood lines of contemporary cars is the result of European pedestrian crash standards. There needs to be at least 1″ in between the hood and the highest hard point in the engine compartment (often the engine) to cushion the fall when a pedestrian gets hit and flipped up onto the hood. Maybe in some cars the high hard point would be the strut towers, in which case suspension packaging would impact the hood line.

        Either way, high hood lines and pillbox designs are form following function, not the whims of contemporary car designers. The pillbox design with side windows shows up when designers decide it is cleaner to follow the hoodline to the rear of the car than create an abrupt drop after the A pillar. For an example of what you get when that line drops after the A pillar, see the MKV Golf. I think it works on the Golf, but wouldn’t on the majority of sedans.

    • 0 avatar
      Dynasty

      “** Other things I’m okay with: rear drum brakes, four-speed automatics, conventional fuel injection and hard plastics where your elbows never go. Does the car do what it needs to do well? Yes? If so, then anything else is sophistry.”

      All those things are fine. But unless the envelope of design is constantly pushed, we’d all still be driving a pushrod V8*, with two speed powerglides. Or building homes out of sticks and mud.

      I agree a lot of things are gimmicky, but as time progresses the bad ideas are dropped, the good ones are refined, and new ones join the pack. Then the good ones which have been totally refined and which people have come to love are eventually discarded for new exciting complicated and unreliable and unproven technology.

      * And I’m totally fine with pushrod V8s.

  • avatar
    George B

    From what I’ve read, the Honda double wishbone suspension is more readily modified for lower ride height. I left my Accord Coupe stock, but I see many that have been lowered. I wish some German engineer had sweated over the details of the Accord suspension tuning to make the ride a little less jittery.

    So far I haven’t replaced any suspension parts in 132k miles, but I live in an area with no road salt and relatively few pot holes. YMMV. I doubt that suspension configuration had much to do with longevity. I suspect that a decade ago Honda was designing cars to last about 10 years without repairs and their engineers selected parts to meet that goal. Other manufacturers, burdened with high legacy costs, aggressively beat up part suppliers to cut costs at the expense of more repairs after the warranty.

    • 0 avatar
      TEXN3

      I can say the same about my 98 3.2TL, original suspension components after 13 years and almost 140k miles. The shocks are getting a bit soft, but the car tracks and drives well. I do need to replace the transmission (not transaxle) mount though.

    • 0 avatar
      geozinger

      @GeorgeB: Your very fortunate to live in an area that has no pot holes and road salt. If you never have, you have no idea how little time it takes to beat up a car any car.

      I’m not buying into the suspicion that Honda was engineering their cars to go 10 years w/o repairs, that just seems unlikely to me. Especially after witnessing (what seems to me) the high number of axles, tie rod ends, struts and etc., that seem to need replacing on all kinds of cars in this environment. Maybe a high end luxury car has that kind of threshold, but mass market ones are built to a price.

      • 0 avatar
        200k-min

        My ’99 Accord had lived its entire life in the rust belt. I can attest that Minnesota pot holes will kill any suspension…even a Honda DW. I replaced all the shocks/coils back around 120,000 mi. A drive axle went out at about 180k but I think that was wear. Sway bar links have all been replaced. But the real bitch is upper ball joints. Those bastards just hate pot holes which are pretty much unavoidable.

        As for high end, they are no different. Know people that have had pretty much same replacement cycles with high mileage Lexus/Acura. Nobody keeps a Bimmer long enough to find out and Audi’s usually crap out before the Japanese.

      • 0 avatar
        golden2husky

        I have found that Honda struts/shocks seem to last longer than most factory units. My MarkVII front struts had lost their edge by 70K, albeit on frost heaved roads. Those people who I know that have Hondas, I have been in their car and I did not notice much degradation until 90K or so and I am very sensitive to the effects of worn dampers…I hate being in cars with worn suspensions…

  • avatar
    Thinkin...

    FYI – the forthcoming redesign to the BMW 3-series has switched to double wishbone suspension up front. And although nobody’s really taking notice (at least not yet), it’s actually quite a significant design change for the car that’s been a benchmark for handling and precision for the past 25 years.

    • 0 avatar
      jhott997

      well there we go, unequal length upper and lower “wishbone” type of suspension architecture *must* be better.
      Wonder when the 911 and the Boxster will migrate from McPherson Strut designs to unequal length “wishbone” suspension.

      • 0 avatar
        chuckrs

        Wonder when the 911 and the Boxster will migrate from McPherson Strut designs to unequal length “wishbone” suspension.

        Tradition demands a return to swing axles.

      • 0 avatar
        srogers

        Yes, buyers and fans of Porsches and BMW 3s need to be told that their cars handle and ride like crap. I wonder if the academic superiority of wishbones is equal to using “pure” tire nitrogen to make cars better.

    • 0 avatar
      Tuce

      The F30 3-Series hasn’t switched from the front struts. The new 5-Series has.

  • avatar
    jhott997

    The rapid decline in the quality of comments on TTAC over the last few months saddens me.
    This comment included. It saddens me that I feel compelled to write this post.
    TTAC has jumped the shark.
    Moving on now…

  • avatar
    stuntmonkey

    I like the ‘feel’ of wishbones, but i don’t know if this was me or not, but my sense is that there’s less ‘slack’ in a strut setup (less linkages, moving parts)… the turn can feel quicker when turning the whee from dead center.

  • avatar
    JimR

    Most people don’t care one bit that they’re driving a positive-cambering, bump-steering, tire-killing hot mess.

    BMW bakes in lots of cleverness into its McStrut setups, including loads of caster. You can’t band-aid everything away, though. Drive a bone-stock RX-8, Mazda6, or Miata. They just work. The composure shines through when the road surface is less than stellar and you’re applying cornering forces.

    The upcoming BRZ/RF-S has some packaging problems due to the boxer engine, but most cheap-driving suspension are just that: cheap. Things like the REVO knuckle or the multilink front suspension on my G20 show just how much tech you can pack into a small space.

    Bottom line cost favors the standard stamped steel lower control arm, one ball joint, a strut, spring, and a few bits to bolt it all together.

  • avatar
    Gedrven

    SLA vs. strut has advantages in front suspensions, where they are far less noticable than in rear suspension setups. BMW in particular used semi-trailing arm rear setups (not quite a strut, but closer to that than a DW), and the lighter E21, E30, and its derivatives, going as late as the Z3 in the 00’s, were known for somewhat twitchy rears once traction was broken. When the E36 3-series came out in 91, the rear got much easier to handle beyond the limit. You can also note that Porsche doesn’t use struts in the rear for much the same reason, though I don’t know if they ever did (the original Beetle used swing arms with the same kind of scary beyond-limit handling as rear struts).

    It should also be noted that at least older BMW front struts aren’t proper MacPherson struts, but have a more complex lower arm geometry that affects camber changes in more subtle ways, especially when turning.

    BTW, I don’t know about the E39 M5, but the recirculating-ball box on the previous E34 (also the E39 540i) is probably the most-hated feature of that car. Contemporary reviews raved about the overall chassis setup and suspension setup, but the steering was always a weak point. 20-some years later, things haven’t improved. The box wasn’t there for feel or handling; driving enjoyment of the car happened in spite of that overweight, overcomplex, slop-tastic and numb contraption, not because of it.

    • 0 avatar
      burgersandbeer

      What’s even worse than the recirculating ball steering is the steering wheel they attached to it on the earlier years of the E39 540. It is commonly nicknamed the boat wheel. At the very least, it belongs in a bus.

      Things did get better though – BMW managed to package rack and pinion steering with the V8s on the E60 5s.

  • avatar
    KitaIkki

    Mazda6 and its platform-mates Ford Fusion and Lincoln MKZ have DW/SLA front suspension. So do Honda Accord and its platform mates Acura TSX, TL and RL.

  • avatar
    ppxhbqt

    The previous-gen NF Sonata used DW up front and ML in rear. The current YF gen uses struts up front and ML in rear. I don’t think anyone will say the previous version had any ride or handling advantages. The big thing is how much travel you give it and how you tune it.

  • avatar
    Seminole 95

    Thanks everyone for their responses. This has been a great education and very entertaining.

    P.S.

    @cdotson, I’d be interested to hear who you think executes the SLA suspension correctly.

    • 0 avatar
      cdotson

      Actually I haven’t taken the time to check out a wide cross-section of the automotive samples of suspension design lately. My experience was primarily in light-duty off-road vehicles but also in FormulaSAE.

      The average FormulaSAE team does a pretty good job of getting it right. I don’t know about too many teams, but it seems like most NASCAR teams follow myth and legend and don’t bother to actually “engineer” a front suspension, which is also common among light off-road vehicles.

      The average American vehicle with SLA front suspension built before the early/mid-90s pretty well screwed it up and/or phoned it in, but much of that may have been a failure to update their methodologies and “tribal knowledge” from the days of bias ply tires to the new realities of radials.

      When the Chrysler LX cars came (300, Magnum, Charger) came out I noticed they had a remarkable design with an incredibly tall upright. You could nearly see the UBJ above the tire! It is a pretty good design, as are many other DiamlerChrysler-era suspension designs. They primarily “borrowed” Mercedes C-/E-class suspension design which have tons of caster, but work really well. Chrysler vehicles have maintained this characteristic since then. Other than these I haven’t bothered to look too much as I no longer have much opportunity to do vehicle design.

  • avatar
    Seminole 95

    P.S.

    @cdotson, I’d be interested to hear who you think executes the SLA suspension correctly.

  • avatar
    racer-esq.

    I think this is a comfort issue more that a performance issue, kind of like the live rear axle on the Mustang. On the right roads my Miata feels much smoother than any car with struts that I’ve driven, but I don’t think they make a critical difference at the limit.

  • avatar
    Beerboy12

    MacPherson strut struts are typically on the front wheels. With a front wheel drive the drive shaft plays a role as part of the suspension, sort of like the upper wishbone. This is one reason why, sometimes, when a CV joint breaks the whole wheel can come off. I believe the main difference is that with the double wishbone set up, wheel alignment issues are less likely to happen.
    My Accord handles surprisingly well. I can chuck it into a sharp turn or take it fast around a long high speed bend and it soaks up both with no fuss or tier squeal.

  • avatar
    Educator(of teachers)Dan

    Meh… worry more about shocks/struts and the bushing that the suspension rides on. That with tires and wheel sizes will have more affect than anything else.

  • avatar
    niky

    I’m in the “comfort” camp. I’ve noticed you can make a double-wishbone front end ride better while maintaining the same handling characteristics (or better) as a stiffer McPherson front-end. The Miata and Mazda6 are wonderful in this regard… though I feel the current Mazda6 iteration has a little too much front-caster for everyday use… it’s still much better in terms of feel than the front end of the BMW 3.

    The MX-5 is simply otherworldly. Double-wishbones and lightness allow it to run a very soft set-up very successfully.

    But in the end, get the suspension tuning right, and you can make anything handle. Even a live rear axle…

    • 0 avatar
      Morea

      … provide the road is smooth. Cornering on broken pavement is the true real world test of a car’s suspension.

      When Colin Chapman said “Any suspension — no matter how poorly designed — can be made to work reasonably well if you just stop it from moving” he was referring to race cars on glass smooth tracks.

      Just listen to racers (and HPDE students) complain if the track surface is not in perfect condition (e.g. Sebring).

    • 0 avatar
      yaymx5

      “The MX-5 is simply otherworldly. Double-wishbones and lightness allow it to run a very soft set-up very successfully.”

      Yup. :)


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