The latest Toyota Corolla has been heavily praised for its newfound dynamic zest. Suddenly, the dullest compact is one of the most satisfying to drive and part of that is due to its trick new double-wishbone independent rear suspension. Where the Corolla hatch may have missed the mark, however, is in its reduced cargo volume. Whether it be for these packaging considerations or simply due to cost, the rest of the segment, including the Mazda3 (above) and Mercedes A-Class, are actually moving partially or entirely away from independent rear suspension. This leaves the Corolla in a shrinking pool of IRS-equipped offerings.
For those unfamiliar with the term, a torsion beam rear suspension uses trailing arms integrated with a crossmember. This is designed to twist as the wheels move, hence why a torsion beam is often referred to as a twist-beam. In short, it’s more sophisticated than a traditional live rear axle but less sophisticated than independent rear suspension. The crossmember can be mounted down quite low, aiding cabin and cargo space, and the set-up is simpler than IRS, often relatively light, and the cross-member also serves as an anti-roll bar.
Mazda, Ford and Mercedes-Benz are the latest brands to switch from IRS to a torsion beam. Mazda’s decision to ditch IRS is at odds with the Mazda3’s more upmarket positioning. In the US, for example, the cheapest Mazda3 now costs $3k more than its predecessor. And though the torsion beam seems to be a cost-cutting move, the new 3’s interior has been thoroughly transformed for the new generation and is richly-appointed with an abundance of high-quality materials.
Though a torsion beam sits nice and low and should therefore improve cargo volume, the new Mazda3 hatch actually sees a slight reduction in trunk space. Mazda has defended the shift to the beam, claiming there are fewer variables when engineering a torsion beam and therefore it’s easier to engineer and fine-tune. They’ve also claimed the switch has helped reduce the Mazda3’s NVH levels which, based on reviews of the new generation, seems to have worked. Few automotive journalists have noticed an appreciable decline in dynamic ability, either.
Another dynamic benchmark in this segment, the Ford Focus, now uses a torsion beam in most models. The smaller Fiesta had always used a torsion beam, even in snappy ST trim. The new Focus has a multi-link “Short Long Arm” rear suspension in all wagon variants and a slightly different version of the system in sports variants. The wagons’ suspension has the dampers sitting nearly horizontal, allowing for more cargo space.
Most Focuses, however, will have the torsion beam, which seems like a step backwards although it does use some of the same parts as the Fiesta ST. In comparing the Focus’ IRS and beam set-ups, Drive found the torsion beam-equipped models still handled excellently but, compared to the IRS models, experienced slight vibration and shake on rough roads. So, there’s not a marked decline in ride comfort and virtually nothing in handling ability. Still, one wonders why Ford didn’t just use the wagon’s IRS in the less powerful hatch models instead of engineering three separate rear suspension set-ups.
Ford C2 architecture chief engineer Michael Blischke went so far as to say Ford only held back from switching the Focus entirely to torsion-beam because of the Focus’ entrenched reputation for dynamic excellence. While that sounds like a humble brag, he explained Chinese buyers in particular value the latest in technology and innovation. Considering Ford’s somewhat shaky situation in Europe and even worse footing in China, retaining the IRS was sensible even if, as Blischke explained, a torsion-beam is arguably fine for 95% of drivers.
GM had already utilized this semi-independent suspension layout in the outgoing Chevrolet Cruze and the now PSA-owned Opel Astra. When PSA launches the next Astra generation – likely to share a platform with the Peugeot 308 – they’ll probably stick with this layout as Peugeot’s 308 also employs it. The same applied to the defunct Citroen C4 and the C4 Cactus, likely to be merged into one model in the near-future. Nissan is another company that’s consistently stuck with the beam, ditching its short-lived IRS from the Sentra in ’95 and not looking back. Partner Renault also uses a torsion beam set-up in the Megane.
Mercedes’ new A-Class has a torsion beam in models at the low end of the range. Mercedes’ compact car development engineer, Frank Weiner (I never sausage an interesting name!), cited the common refrain of the torsion beam set-up’s weight and packaging advantages but also highlighted the need to future-proof the A-Class platform for electrification.
The new A-Class’ program manager, Oliver Zolke, told GoAuto the change was driven by the weight reduction available with the torsion beam. The total weight saving? 44 pounds. That doesn’t seem that impressive but Zolke went on to say this freed the engineers up to do some extra stiffening and stretch the wheelbase. Zolke also believes the torsion beam set-up allows for greater ride comfort so make of all this what you will.
Like Mercedes and Ford, Hyundai and Kia offer IRS only in sportier versions of its Elantra, i30 and Forte/Cerato compacts. Though the Elantra’s trunk volume is the same size regardless of suspension set-up, the IRS models have a space-saver spare while the torsion beam models have a full-size one. The dynamic divide between the two suspension set-ups seems to be more apparent in the Hyundais, critics generally finding the IRS models to ride and handle better. Perhaps because of this, the European Ceed, related to the Forte/Cerato, is IRS-only.
This widespread return to torsion beams in the compact segment seems to be a historical correction. Volkswagen only switched to IRS with the Mk5 Golf, coming shortly after the first Ford Focus and its Control Blade IRS; the current Golf range features IRS in some models, torsion beam in others. Of VW’s other C-segment offerings, all on the MQB architecture, there’s one that exclusively uses torsion beam (Skoda Scala), one that uses it only on base models in some markets (Audi A3), and two that use it on all bar sporty trim levels (Seat Leon, VW Jetta).
Honda is somewhat of an outlier here, exclusively using IRS on the current Civic. Alfa Romeo switched to IRS with the 2000 147 and the Giulietta retains that set-up, while the Subaru Impreza is also equipped with IRS.
Whether it’s to eke out a little bit more trunk volume or (more likely) to save money, IRS is rapidly disappearing from the compact segment right as Toyota introduces a new Corolla with it. Has Toyota misjudged compact buyers’ expectations? Is the promise of a slightly smoother ride and better handling at the limit worth a reduction in cargo volume? Though the less sophisticated beam arrangement is anathema to enthusiasts and smacks of cost-cutting, compacts equipped with the torsion beam don’t seem to be demonstrably disadvantaged dynamically. It’s possible to engineer a car to ride and handle commendably with such a set-up. If you insist on IRS, however, be prepared to pony up for up-level variants. Or just buy a Civic or Corolla.
“Here’s Why The 2020 Mazda3 Has A Torsion-Beam Rear Suspension” – Craig Cole, AutoGuide
“Benz defends A-Class switch to torsion beam rear end” – Daniel DeGasperi, GoAuto
“New Benz A-Class hybrid drove torsion beam” – Byron Mathioudakis, GoAuto
“Ford Focus 2019 review” – Alex Rae, Drive
“Why most Ford Focus models ditch IRS” – Byron Mathioudakis, GoAuto