BMW E36 Blog

I’m sure that many of you guys will be interested in knowing why BMW M3 cars handle so good. This is an article that Jim has sent me couple weeks ago. I think this article is great and since it’s too long, I decided to make it on 2 parts, this is the first one. If you like this post, I will be posting the second part very soon, so stay tuned and let me know what you think.

This article was published on the Motor Trend Magazine (November 1998)

By Kim Reynolds

It’s 11:00 A.M. and Contributing Editor Paul Van Valkenburgh, Road Test Editor Patrick Hong and yours truly are lost in concentration. Video screens are painting our faces with the glow of computer-generated stock cars sliding through the streets of San Francisco, rock-scattering rally cars slithering precariously near mountain-edge precipices, and mighty Indy cars hurtling past blurred super speed way grandstands. Behind us, kids walking past our video game stations at the Park Palace amusement arcade are giving us odd looks, and not just because we’re the oldest gang of truants ever to set foot in the place. The odd looks are because it’s obvious that we’re not really playing these games; we’re just twisting the steering wheels back and forth, holding their rims with the ends of our fingers.

What’s going on here? Shush…this is research.

In fact, we’re in search of one of the automobile’s most elusive and abstract properties – steering feel. Quite frankly, of all the things I want to know about cars, understanding steering feel is very near the top of the list.

It’s such a mysterious, ethereal thing, steering feel. I mean, how does it happen that when I close my eyes for a few seconds while behind the wheel of a great-steering car, the wheel’s torques and tiny kickbacks manage to conjure in my mind such an accurate rendering of the road’s texture and the tire’s dynamics? It’s analogous to how our gray matter can translate the vibrations of a phonograph needle upon a record into a Bach fugue, a Benny Goodman solo, or the Beatles’ White Album.

But enough abstract philosophizing; what the heck is mechanically going on between my hands and the road surface to engender such communication? To get to the bottom of it, we borrowed a BMW M3, arguably the world’s current prime example of proper steering feel.

Hoisted in the air atop our garage lift, the M3’s underbelly yields no obvious clues. There’s a robust structure of welded steel tubes corseting the engine’s belly, no doubt greatly stabilizing the M3’s front suspension geometry. Pokes with an X-Acto knife at the synthetic bushings isolating the ZF steering box from the subframe identify them as unusually stiff. A notably stout structure, but so far we’ve uncovered no big answers.

However, wrap your hands around the M3’s steering wheel while it’s idling and you’ll notice there’s a remarkable amount of engine vibration being transmitted up through the steering column. The wheel’s rim almost hums, a characteristic we’ve come to closely associate with small BMWs. A clue perhaps? Being a suspicious sort, I immediately deduced it to be a deliberate engineering ploy to enhance the M3’s impression of low-speed road feedback by sneakily feeding-in engine vibration. Paul, more clever than I, postulated that the vibration might be a smart way to continuously break up the steering gear’s natural stiction, resulting in an impression of unusual fluidity. These BMW guys are geniuses!

Smug in our penetrating insights, I addressed the question to the Bavarian Motor Works. Answer? It’s just something they can’t get rid of. Great steering feel, they stated, requires a very solid structure with minimal flex anywhere in the steering gear. In other words, that steering rack I noticed so rigidly mounted to the engine’s subframe just can’t avoid also being awash with the inline-6’s tremblings. According to Munich’s engineers, the steering wheel’s buzz is simply part of the deal. Lesson one: Minimal compliance is the first ingredient of sensitive feel.

All right, then how about an element that’s vastly less stiff – the tires? A call to the M3’s tire supplier, Michelin, put me in contact with Dr. Bill Post, whose specialty is just this sort of thing. The good doctor’s most interesting point on the subject, and an entirely unexpected one, is that the most under-appreciated factor in facilitating linear steering behavior is a good rear suspension. Rear suspension?

Dr. Post explained that when you turn into a curve, steering linearity relies enormously on the rear tires loading up with cornering forces in a nicely progressive manner. If there’s anything unpredictable about the car’s rear end, it’ll destroy the car’s steering quality. Makes sense.

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