God is in the Details : 2015 Subaru WRX STi

God is in the details, as Mies Van der Rohe said. Subaru’s recent WRX STi has attracted my attention with an engineering choice that deserves respect.

2015 Subaru WRX STi
2015 Subaru WRX STi

I have two reasons for this article. One is the subject itself, Subaru’s devotion to steering quality, and two is to make up for our neglect of the brand. During our recent foray into engines, DTW failed rather spectacularly to mention Subaru who have championed boxer engines on the grounds that these make for a car with a lower centre of gravity, to the benefit of handling among other boons.

As LJK Setright noted, lowering the centre of gravity is a more effective means to ensure stability than widening the track of a vehicle.  Furthermore, Subaru have developed a boxer diesel engine in order to reap the economy advantages of diesel, while still retaining their signature engine layout. This is worth noting in these days when Fiat throw their engines into Alfa Romeos and PSA have no opinions on engines at all.

I will have to return to that boxer diesel at another time because, in this post, I’d like to consider Subaru´s decision to engineer a hydraulic rack for the Subaru WRX STi despite it being a very specialised model. The numbers involved are in their thousands, a fraction of the overall sales of the WRX generally. They could so easily not have bothered and still have had a good car. But they did bother and I think that’s worth a closer look.

Why did they do this? While the standard WRX’s electric rack is already on the good side, Subaru felt that a hydraulic rack would help further improve the steering feel and precision. For a car as focused as the WRX STi, to have not have made this decision would have been inconsistent, given the long list of other modifications that set the STi apart.

What is steering feel? Philip Harnett’s PhD thesis (2002), ‘Objective Methods for the Assessment of Passenger Car Steering Quality’, has a section which is a good introduction to the matter of steering quality or “feel”:

“Reynolds [1998] describes steering feel as one of the automobile’s most elusive and abstract properties. He emphasises its importance when saying: ‘Of all the things I want to know about cars, understanding steering feel is very near the top of the list’. This comment is representative of many individuals, as steering feel is a term used copiously in connection with the evaluation of passenger cars by the industry, press and the public. Almost everyone involved with or enthused by the automobile will have an opinion on what steering feel constitutes and what represents ‘good’ steering feel.”

Harnett goes on to say: ”Zaremba, Liubakka & Stunz [1998] …write that steering feel is effectively defined by the steering wheel torque the driver senses during steering manoeuvres and by the vehicle response to steering inputs.”

In the light of the importance of steering quality, Subaru made a set of revisions to the STi version of the WRX to maximise this aspect of the driving experience. As something of a steering fetishist, this struck a chord since, regardless of your speed, you always have to steer. Why not make the only constant point of contact (other than the seat) as good as possible? If there is an easy (and strangely overlooked) way to make a car pleasurable to drive, it’s through tuning the steering system.

I asked Subaru’s UK press office for a little information on this so as to see what Subaru did to offer a better set-up for the 2015 STi’s hydraulic rack. The changes included a quicker gear ratio than on the standard car, stiffer hydraulic power steering torsion bars, optimized power steering assist characteristics (presumably the rate and amount of assistance) and an increased spring constant for steering gearbox mount bushings (up by 400%).

A quick look at Hooke’s Law will remind you that the spring constant is a value for each spring determining the amount of force needed to stretch or compress it a given amount.  In layman’s terms, it means stiffer bushings, and that reduces play in the rack when high forces are applied.

2015 Subaru WRX STi interior: robust, in the Subaru tradition,
2015 Subaru WRX STi interior: robust, in the Subaru tradition,

According to Subaru “a quicker steering gear ratio and more rigid system have reduced response lag from lateral G-forces when steering for steering precision and made for a more rigid feel.” At high speeds and under tricky conditions the response lag becomes all the more important. The idea is that the driver inputs should be matched by proportional and direct outputs, and presumably that signals sent back from the wheels should be accurately communicated to the driver too.

Response lag muddies those signals. Ideally the phase lag should be in the range 0.0 Hz to 0.4 Hz . Above that, things get confusing.  The steering gear ratio was reduced, the more so on the RHD models where it is now at 12.7, which requires less input for the desired steering output. As you can see, this all builds up step-by-step to create clearer and more linear controls.

Road & Track´s views of the changes to the steering are as follows: “So precise is the steering that you can select an inch-square hunk of apex pavement and hit it lap after lap. Steering this quick should be darty, nervous, prone to kickback. That it evinces none of those traits is evidence of rigorous development.”

I’ve focused on the steering rack and its effect on steering feel, but for a more general review of the car, you can read Road & Track’s views by clicking here. I note that Road & Track reports that the a-pillars have been made narrower – is this a first in recent years? The other thing I like to do when steering a car is to see what’s in front of me. Thick pillars don’t aid that goal.

Given that the main focus on automotive design is in the gadgets category these days, it’s heartening to see Subaru carrying on with putting engineering first. The next step for steering technology is to try to put back what electric steering has lost. I can see the economy advantage of electric steering for many cars but, at the same time, it reduces involvement and, in a way, detaches the driver from the driving.

The cars I have liked best are the ones whose steering I can remember and I think that’s not a coincidence.  You can see why Subaru has such a loyal following.

A full set of details of the car can be found here.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

5 thoughts on “God is in the Details : 2015 Subaru WRX STi”

  1. I have great admiration for Subaru’s engineering, and am pleased to see they are putting work into good steering, which really is one of the pleasures of driving. At 12.7:1, the steering ratio is at the fast end and with good feel should be fine, though I should point out that a Citroen SM’s steering was quoted at 9.4 :1. That car’s steering was also not darty, nervous or prone to kickback but, of course, it had no feel at all. The Citroen shows (or should have shown in a sensible world) that precise, low input steering has a place outside the world of sporty cars. So that’s why I’m disappointed that such a set-up isn’t available in the more mundane Subarus.

    As you say, Subaru retains a loyal following and, even outside owners, it has masses of goodwill. Twenty years ago the WRX seemed hugely attractive to me. It’s not that I’ve got older, but roads and policing have changed so much that it seems irrelevant today. Is the WRX a distraction for Subaru? If it didn’t have that as a halo, would it feel more inclined to produce some really distinctive cars at the lower levels. I guess that suggesting to Subaru that it should be the 21st Century Citroen is hardly tempting for them, when they consider what happened to Citroen, but that’s really what I’d like to see.

  2. Richard has made me feel guilty too about not speaking up for Subaru. I remain a fan of the marque, having been an owner of Spec-B Legacys beween 2006 and 2011. These cars were possessed of the delightful 3.0 litre H6, which is the nicest engine I have ever encountered, embued, like the rest of the car by a very mechanical feel to everything. The gearchange was a little clunky, but also felt connected to something substantial. You could hear the LSD working underneath the car. The steering had a lovely broad-shouldered feel to it (especially in the facelifted model). All in all, a very robust-feeling car that gave me no trouble (come to think of it, WHY did I replace it with a C6?). Some might have described such things as showing a lack of refinement, but I always sensed that Subaru wanted the owner/ driver to feel that connection with the engineering, rather than marvel at the “infotainment architecture”, or whatever. Such a stubborn approach does seem to be being proved wrong by market performance (in the UK at least), but I have admired their integrity/ arrogance in sticking their tongue out to the rest of the world. Except that those days now seem numbered, if not already departed.

    Since the mid-noughties, it has seemed to me that Subaru has been kissed by the customer clinic effect. My beloved Legacy was definitely a victim – larger rear door apertures, over-emphasised wheel arches (because people are too thick to realise the cars are AWD without such a styling trick – apparently), larger headlamps … they were all ushered in following “feedback” and the result was an uglier car. The Forrester, which could once have claimed to be the original “cross-over”, has become a “proper” SUV just as “cross-overs” have become the vogue. The rushed (and nasty) XV is little more than a jacked-up Impreza, and in unsophisticated next to a Yeti or Quashqai. The BRZ is refreshing in holding the line (but why no turbo or AWD?), but is an enthusiasts choice which is not selling even to enthusiasts (see this month’s EVO if you want proof).

    You see, like Citroen, I’m holding out for a day when Subaru produces something to give me an excuse to buy one, again, but it’s proving a long wait. I once thought that the Holy Grail was a car styled by Alfa and engineered by Subaru – given recent developments in both arenas, I’m not quite so sure any more, even if, as, Richard points out, some of the old engineering spark looks like it is still there.

  3. SV. I remember toying with the idea of a grey import GT/B Legacy Estate in the mid 90s and, on and off since, I have been tempted by Legacys. It sounds as though they have all the virtues of my aged Audi S6 Avant, plus a few more (like steering feel!) Why did I never get one? I’m not sure, though the fact that the Audi’s bright blue paintwork and co-ordinated seats sealed the deal probably shows that I am just too superficial a person to deserve Subaru. And the fact that the World is full of people like me might be one of their problems. For all their pandering to the Scooby crowd, they remain an oddly unworldly company in many respects.

  4. I may not be the most astute, but I found nothing to criticize on the steering response and feel of the electric boosted Honda S2000 I owned for 100,000 miles. I never faced it off against the Subaru you describe herein on the same afternoon (or ever) so perhaps I might have quantified some difference, however nuanced. At any rate, I think I am more interested in the BRZ today, whatever it uses. Also curious to learn if it and its sibling Scion got different rack bushings. I retired from Ford over a decade ago, but remember obtaining overall steering component rigidity throughput was a stated consideration in selling a new rack gear for the Lincoln Towncar.

  5. I may also fall in “steering feel” enthusiast category.
    Somebody once wrote that it’s actually a steering that gives you primary information about cars behavior, about 0.2 seconds before what your eyes see……
    And really, having driven quite a few modern cars, they all seemed to lack honest, direct steering feel of non-asisted Peugeot 205 on narrow 155 tyres, or even my Yugo!
    One of the inexplicable, almost irrational reasons I enjoyed driving a Yugo more than my old Mazda 3 diesel was probably due to more steering feel, although coming at the expense of rather slow rack.
    Well, you can’t have it all… 😉

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