Getting the steering right

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Andrew Frankel

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Earlier this year BMW posted a corporate video on YouTube. In all regards bar one, it is entirely unremarkable. A man gets into an M235i on a test track and drives off. The car is then put through a series of manoeuvres including a slalom test and a deftly held drift on a wet steering pad.

So what? So not very much were it not for one small fact I omitted: soon after setting off, the engineer presses a button and takes no further part in the test, all of which including the slalom and skid, is executed with inch perfect precision by the car alone.

With the government rightly fast-tracking the testing of autonomous drive cars on our road this is a fairly hot topic of conversation right now, but it is not what I want to write about today. The question that video poses to me is: why, now BMW is clever enough to make a car steer by itself, why on earth is it incapable of fitting a decent steering wheel to its highest performing models?

As the primary interface between man and machine, there is no single component with a greater influence over a how a car feels than its steering wheel, yet if you go and buy a brand new BMW M4 you’ll find it equipped with a thick squishy rim through which any road feel is effectively sponged away. Interestingly, if you buy the Alpina equivalent – the similarly powered and priced B4 – you’ll note one of the first thing the tuning company does is fit a wheel with a far firmer edge.

When I bought my old 911 – a replica of a 2.7 Carrera RS – the first thing I did was swap the horrid wheel with which it came for a Momo with a hard rim and none of the other many things I did to the car thereafter came anywhere near transforming the car in the way the new wheel did. In fact I wanted to fit a 2.7 RS wheel which is one of the most gorgeous and best designed of them all, but I could not find one and would not have been able to afford it if I had.

BMW may be at fault for its wheel rim stuffing material, but its steering systems are in other ways close to impeccable, unlike most. Steering is the first place engineers look if they want to cover their car’s dynamic failings.


Alpina’s B3 with upgraded steering wheel

Got a car that’s too heavy? Give it a really quick rack so you get a big deflection for even the smallest input and you will fool some. Want to make your long wheelbase car feel more agile? Give it a variable ratio so it’s initially very aggressive off centre. Or the oldest trick in the book: fitting a car with a small, thick rimmed wheel because that’s what racing cars have.

Or you can make your car steer as it should whether it is sporting or not. The wheel should be quite large because it’ll be easier to use that way and provide a clearer view of the instruments. Its rim should be as firm as possible without actually being uncomfortable to hold. Its gearing should be slower than modern sporting car convention suggests, with a little less than three turns from one lock to the other for a car with an average turning circle.

And, above all, it should be linear in its response, so that a given input produces a reliable and predictable reaction every time. Not difficult is it? But still apparently beyond the reach of most car manufacturers today.

 

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