By on October 5, 2018

2015 Hyundai Elantra rear torsion beam suspension, Image: hyundaipartsdeal.com Sam writes:

I have a 2015 Hyundai Elantra SE. It has 25,000 miles and serves its purpose of a street parked commuter car that is comfortable enough for the occasional 600-mile round trip on weekends. The only real issue I have with the car is the cheap-car torsion beam rear suspension. Over large bumps on one side of the car the rear of the car feels like it oscillates extremely in each direction.

In a straight line it is controllable but I worry that in a off ramp taken a little too fast that a unseen bump could actually upset the car enough to lose control (or surprise a fiancé who is used to the handling of a 200S). The 2007 Honda Fit and 2015 Chevy Volt I drove I believe have similar setups but didn’t feel at all like this, and neither did the 2011 Crown Victoria I drove. I’ve read online that some aftermarket replacement shocks would help with this.

Is this really the case? Would a lighter set of wheels also help?

Sajeev answers:

Of course the Crown Vic won’t skip about: Panther Love for dat Watts Link, Son! 

Seriously, the number of reasonably adjustable variables (i.e. keeping factory pick up points) provide a staggering number of end results to vehicle performance. And just because a suspension expert journalist gives you two cents doesn’t mean you or your fiancé agree. Perhaps only a tire pressure change is needed?

If not, the Hyundai Elantra’s torsion beam bump steer (more precisely roll steer) could merit a spring/shock upgrade, or a bolt-in upgrade from Pierce Motorsports or Progress Technology. I’ve enjoyed the latter: the ancient TTAC review has yet to sour after 9 years and 60,000+ miles, though I’d love to dial out some sway bar to add spring and/or shock firmness.

Such theories are only great in vacuums. However, owner feedback from Hyundai forums suggest aftermarket shocks also fit the bill: there’s a KYB Gas-A-Just performance rear shock available.  Will a higher performance rear shock adversely affect ride/handling with original, 3+ year old dampers up front?

Only YOU know what’s right. I’d tinker with rear tire pressures first: try ’em on the same bumpy turn at the same speeds.  If you still demand satisfaction, keep the factory suspension intact and slap on those aftermarket torsion bars. Even better, this is such a well known problem you can likely sell it on Craigslist and claw back some cash after you sell the Elantra!

BONUS!  A Piston Slap Nugget of Wisdom:

We’re overlooking the handling band aid nanny available in damn near every late model car: standard electronic stability control. Provided you’re driving to the road conditions, not sawing at the steering wheel back and forth (i.e. rocking the car into body sway), and have good tires with plenty of tread, this problem is a non-starter. 

[Image: hyundaipartsdeal.com]

Send your queries to [email protected]m. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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15 Comments on “Piston Slap: Torsion Beam Bump Steer Solutions?...”


  • avatar
    gtem

    It’s a new Elantra under warranty, leave it alone, it handles fine.

  • avatar
    greaseyknight

    You say it happens when you go over bumps on one side for the car? Makes me think that one of the shocks have failed? Try the bounce test, and then do a good visual inspection to see if any parts have failed. Yes it’s 3 years old, but stuff happens.

    In re-reading what you wrote, I see that it only has the condition when a single rear wheel (either side) hits a bump. It’s still do the bounce test and a visual inspection, start with the basics.

  • avatar
    IBx1

    It’s a hunday; you knew what to expect.

  • avatar
    don1967

    The Elantra’s torsion beam setup is very sensitive to tire pressure, so if you’ve got more than the recommended 32 psi you need to dial it back. It only takes a couple of extra psi to make the rear end significantly more skittish.

    That said, many owners report dramatic improvement with the KYB shocks.

    • 0 avatar
      PrincipalDan

      Recommended pressure (on that nice little sticker on the door jam) is there for a good reason. Generally it is the best compromise between ride and handling.

      My Highlander recommends 30 PSI, which is where the tire shop makes sure it is set every time I do a rotation. Makes the ride very cushy with 65 series tires.

      The dealer however – every time they do an oil change sets it at 35 PSI because it keeps the TPMS from freaking out when the temp drops. Makes the ride bouncy to the point where my wife can tell the difference (and she’s no enthusiast.)

      • 0 avatar
        Featherston

        Some Toyotas and Lexuses actually have an owner’s manual instruction to add an extra 3 psi for extended driving over 100 mph. I find it both amusing and optimistic. Alas, the vision of a North America where I could drive an Olds Turnpike Cruiser or an Avanti from one Mad Men-style city to another on pristine, lightly trafficked highways never came to be.

        But 5 psi? That’s annoying. Totally agree that recommended pressure is there for a reason. Absent a well-researched finding that a given vehicle needs to be changed from the original factory spec, I’m casting my lot with the people who have engineering degrees and designed the car.

  • avatar
    notapreppie

    I sometimes get a similar feeling in my RX-8 with its multilink rear when one wheel hits a bump that the other one misses. The tail feels like it’s trying to skitter in one direction or another.

    It’s my indication that my rear alignment is out a hair. I roll up onto my buddy’s alignment rack and set the rear toe to zero and it’s all good again.

  • avatar
    DenverMike

    It’s the same unsettling feeling you get in any pickup truck or Mustang, unless IRS. For a nanosecond, yes you are going sideways and you think you’re gonna die.

    It’s irrational, you’re perfectly fine, even if you do crash. But at that point, you did a bunch of things wrong and no doubt would’ve crashed anyway, even with IRS.

  • avatar
    bludragon

    I don’t think an aftermarket (stiffer) rear sway bar is the answer here. Stiffening up the rear is going to make the car less stable, and more likely for the rear to come around.

    This sounds like it is more than a tire pressures issue, but that is the easiest thing to check.
    Shocks are definitely worth looking at. Has it always done this, or is it worse than when new?
    Wheel alignment is also worth checking.
    Take a look at the condition of the tires as well. That might point to one of the above being a problem.

  • avatar
    Dan R

    Torsion beam suspension is a very elegant solution to rear wheel handling. Your problem does not lie with the setup. Tires, tire pressures, shocks?

  • avatar
    rpn453

    I’d check everything back there, but focus on the bushings.

    Any chance you have mismatched tires? I couldn’t believe how badly that affected my R50 Pathfinder. It was like it had randomly activated electronic rear wheel steering whenever there were any grooves in the road.

    Some new KYB shocks would probably improve the ride and handling regardless of the condition of the OE shocks.

  • avatar
    Greg Locock

    Rear twist beam suspensions have a couple of problems when it comes to steer over single wheel bumps. One is that the whole axle steers in response to the inevitable longitudinal force as it hits the bump, the other is that twist beams always have some roll steer, and in a single wheel bump you get half the roll steer, if you see what I mean. These can be reduced (I hesitate to say eliminated) at the design stage by an appropriate choice of hardpoint (usually unfeasible) and rather fancy bushes. Between those two some manufacturers manage to keep it together. Some don’t.

    Altering the vertical forces is a roundabout way of coping with a steer problem, but once you’ve got the geometry and bushes defined that’s your only tuning knob. The reason it is disconcerting is that there is little feedback that it is occurring via the steering wheel, whereas front suspension single wheel bump kicks back through the wheel, so at least you know where it is coming from.

  • avatar

    I won’t buy a car with Torsion Beam Rear suspension. Even my Base 1.4 Jetta has IRS, although the much hyped new MQB version again goes back to sold rear axle, VW assuming that if you care, you’ll buy a Golf.

    • 0 avatar

      Torsion beam is adequate for 99% of drivers in 99% of daily driving. The other 1% is why the walls of freeway off ramps and flyovers have those big ugly crash marks on ’em.

      The 101 South to I-10 Eastbound ramp in Phoenix has not one but two lovely expansion joints / gaps designed to give the drivers of torsion link cars a little excitement.

      Torsion link rear suspensions should be illegal.


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