<VV> Steering / some Corvair

[Kenneth E Pepke]

On Fri, 3 Jul 2009 16:09:56 +0100 "Alan and Clare Wesson"
<alan.wesson at atlas.co.uk> writes:
> snip <
> 
> 
> Steering is the single most important aspect of vehicle design 
> (apart from 
> the gear lever and the seat base it is your only point of contact 
> with the 
> vehicle). And the tyres, your interface with which it controls, are 
> your 
> only point of contact with the road.
> 
> And it is the issue where I can best illustrate my oft-repeated 
> statement 
> that new is not necessarily better (in fact in the case of steering 
> new is 
> definitely worse).
> 
> The three issues governing steering quality are weight, feel and 
> gearing. 
> The weight of the steering is influenced by three things: a) the 
> weight of 
> the vehicle; b) the width of the tyres; and c) whether the car has 
> front-, 
> rear- or four-wheel drive. A light vehicle with narrow tyres and 
> rear-wheel 
> drive will naturally have light steering. If you increase the weight 
> of the 
> vehicle, the width of the tyres or switch from rear wheel drive, 
> those 
> factors will result in an increase in weight at the steering wheel 
> rim.


I would like to offer a 4th ... but put it in position #1.
Scrub radius.

Optimum steering is quite a subjective subject.  Manufacturers
put a bit of thought into packaging, weight bias, and cost.  
Customer needs / skills are also a major factor.  Too quick
and too positive steering will most likely cause the average
driver [95+% of buyers] to over correct  [The best illustration
I have seen concerning over-correction is the Falcon in the GM 
movie about the Corvair called 'Car on Trial'] and in the case 
of higher center of gravity vehicles this can result in roll over.

Back in the day when I was building late model stock racing cars
my choice of steering was a manual recirculating worm and sector
gear box from GM with the optional quick steering worm.

Rules required these racers to weigh a minimum of 3250 lbs.
Ours was powered by a 427 Chevy stroked to 467 cu in. and
driving the rear wheels.  Class tires [tyres] had no tread pattern
and an 11 inch wide contact patch.

Most of these cars created a great deal of fatigue in the driver
and rack and pinion steering increased that problem.  Adding 
power steering reduced the strength required and even helped
to cover up the harshness of the R&P system.  Of course, I 
did not want to give up horsepower to drive a power steering 
unit so I contracted a major wheel manufactruer to custom
build wheels that would maintain a 1 inch scrub radius.  The
steering effort was low enough that virtually anyone could 
drive and even park this car.  This was not a great break
through or discovery on my part.  The Chevy Suburban with
manual steering we used as a tow vehicle had the very same
1 inch scrub radius. 

To reinforce Alan's statement concerning newer not always 
being better ... The steering wheel effort of current models
equiped with power steering is now greater than that old
Suburban or any Corvair with manual steering!
Ken P




> 
> The way that the weight of the steering at the wheel rim can be 
> controlled 
> (i.e. reduced) is by making it more low-geared (i.e. increasing the 
> number 
> of turns from lock to lock). The ideal is 2 - 2.5, because that 
> means you 
> almost never have to 'shuffle' your hands round the rim, and can 
> turn the 
> wheel very fast in an emergency situation. In the 50s most cars had 
> narrow 
> tyres, rear-wheel drive and 2-3 turns from lock to lock, and the 
> steering 
> was fantastic - extremely 'nervous', and giving you a sense of 
> intimate 
> contact with what was happening under the tyres (which, if you think 
> about 
> it, is pretty important from the point of view of controlling the 
> vehicle, 
> as it is your only feedback of information about the road surface 
> you are 
> travelling on). So if you encounter a patch of ice, mud or oil, or 
> the car 
> begins to slip or slide for some reason (intentional or 
> otherwise...), you 
> are instantly aware of it and able to control it.
> 
> Here is a timeline explaining how those issues have been compromised 
> by 
> industry developments, and why the steering on cars circa 1955 
> really was 
> better than it is now.
> 
> 1955-65 - rear wheel drive, average weight about 750 kg, tyre width 
> about 5 
> inches, gearing 2-3 turns. This was the golden age - it would be 
> very hard 
> to improve on this.
> 
> 1965-75 - rear wheel drive, average weight about 850 kg, tyre width 
> about 
> 5.5. inches, gearing 3-3.5 turns. The slide from perfection is 
> beginning, 
> influenced at first by increasing weight and slightly wider tyres.
> 
> 1975-85 - rear wheel drive, average weight about 800 kg, tyre width 
> about 
> 5.5 inches, gearing 3.5-4 turns. A bit worse than 10 years before 
> but not 
> much.
> 
> 1985-95 - front wheel drive, average weight about 950 kg, tyre width 
> about 6 
> inches, non-powered steering, gearing has to be quite a bit lower to 
> 
> compensate for the extra weight, FWD and tyre width. Mostly 4-4.5 
> turns lock 
> to lock, which feels very low-geared when being driven, and means 
> that if 
> you lose grip on a slippery surface you are unlikely to be able to 
> turn the 
> wheel fast enough to 'catch' the car. Andrew's Clio is one of this 
> generation, and although Renault are better at engineering steering 
> than 
> most, I surmise that it will be around 4 turns if you go out and 
> twirl the 
> wheel.
> 
> 1995-2000 - front-wheel drive, average weight about a tonne, tyre 
> width 
> 6-6.5 inches, hydraulic power steering. Gearing can be improved 
> because of 
> the power steering, and so goes back to about 3 turns lock to lock 
> (Alfa 
> Romeos are 2, which is the best available). Satisfactory 'feel' 
> because the 
> hydraulics allow that, but not as 'nervous' as the non-powered 
> steering of 
> the 50s. As the power steering is one of the many factors adding to 
> vehicle 
> weight, the cars from this period are also less economical than the 
> generation before.
> 
> 2000-2009 - front-wheel drive, average weight about 1.25 tonnes (a 
> Golf 
> weighs about 1400 kg), tyre width about 7.5 inches, electric power 
> steering, 
> about 2-3 turns lock to lock, but no sensation of being actually 
> connected 
> to the wheels whatsoever.
> 
> Vehicle weights now so high that manufacturers are coming under 
> heavy 
> pressure from the environmental lobby and the EU to reduce them (and 
> so 
> reduce fuel consumption), and so are looking for ways to achieve 
> this. One 
> way is to replace the hydraulic power steering with electric. This 
> reduces 
> the drag on the engine (is it not belt driven) and also reduces 
> weight, but 
> offers nowhere near the quality of steering feel. The gearing can at 
> least 
> be kept satisfactorily high, so a typical 2009 vehicle has 
> high-geared and 
> extremely light steering which gives no sensation whatsoever of 
> contact with 
> the road.
> 
> So we have made our cars massively heavy (which makes them worse to 
> drive 
> and less economical) and then sought to alleviate this slightly by 
> saving a 
> few kg by fitting electric steering, which makes them even worse to 
> drive 
> but gives a minute improvement in fuel consumption.
> 
> And that, ladies and gentlemen, is why steering nowadays is 
> considerably 
> worse than 10, 40 or 50 years ago (but only a bit worse than 20 and 
> 30 years 
> ago). I am not making it up - it is an uncontroversial statement and 
> easily 
> demonstrated, and the reasons lie in the design priorities forced on 
> the 
> manufacturers.
> 
> It is just that we have got those design priorities all wrong...
> 
> Cheers
> 
> Al
> 
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