I am not certain it will happen: I hope so.

As time has passed, the development of ultra light-weight vehicles has become a more important theme for AutoSpeed (and this blog). It’s rather like our longstanding acceptance and enthusiasm for hybrid vehicles: it’s a change in transport architecture that simply makes sense.

(Of course, ultra light-weight vehicles have existed previously – especially just post-World War II with the German and British three wheelers. But over the last 50-odd years, there have been almost none produced.)

So what do I hope will happen? The development of an increasing number of such machines.

If that occurs, especially on an individual constructor level, then people will face some unique and very difficult problems.

We tend to take for granted developed automotive technology, and to see engineering solutions only within that paradigm. But when it comes to ultra light-weight vehicles, that’s simply wrong.

For example, take Ackermann steering – that’s where when cornering, the inner wheel turns at a sharper angle than the outer wheel, resulting in no tyre scrubbing. If I was to say that I have spent the last three days struggling with Ackermann steering, some people would laugh.

“It’s all in the books,” they might say, “just angle to the steering levers inwards like this diagram shows. Been done a million times. Next problem?”

But you see, that solution largely applies only if steering like a car is used – with a steering box or steering rack.  And, for ultra lightweight vehicles, both steering boxes and steering racks (or, any currently available, anyway) are way too heavy. 

So, how do you achieve Ackermann steering without a steering box or steering rack?

Australian recumbent pedal trike manufacturers Greenspeed have some brilliant solutions. (Disclaimer: my wife sells Greenspeed trikes.)

One of their approaches looks like this (the drawing is not to scale.) The system uses wheels that turn on kingpins, two steering tie-rods, and one central linking member turning on an offset pivot. The steering is by handlebars; these connect at the points marked ‘H’ and have a motion that is a combination of both sideways and fore-aft.

This steering system achieves full Ackermann compensation, and requires only four rod-ends and one pivot point. (These are in addition to the two kingpin pivots.)

That is simply an incredibly light and effective steering system.

I recently spent day after day coming up with alternative steering systems for my recumbent pedal trrike – and then building them. It’s quite easy to end up with steering with two kingpins, six rod-ends and two pivot points – typically, about 50 per cent heavier than the Greenspeed system!

Making things more difficult for me was that, unlike the Greenspeed trikes with the above steering system, my design uses long-travel suspension. And, getting rid of bump steer (ie toe changes with suspension movement) is another nightmare.

Again, people will be thinking only in an automotive paradigm.

“Bump steer? That’s easy – just set the length of the tie-rod so that it’s the same as the distance between lines drawn through the upper and lower ball-joints….” (and so on).

Trouble is, my suspension system doesn’t even have upper and lower ball-joints… Instead, it’s a leading arm, torsion beam, dead axle with a Watts link.

Shown here is (another) rough diagram. In fact, this is pretty well how my system is with Ackerman compensation and zero bump steer. (The really knowledgeable amongst you will have picked a slight error in the drawing.)

The point is that none of this design can take lessons straight out of textbooks – especially automotive textbooks. Of course, the fundamental elements (like the Watts Link, the concept of Akermann steering correction and so on) are all well documented, but in unique applications, actually applying those ideas is another thing entirely.

I am not setting out to suggest I am some kind of hero – all the designers of solar race cars and pedal-powered tadpole trikes have tackled the same ground. But what I am saying is that the challenge is massive, that achieving a good outcome in terms of suspension and steering dynamics – all at a weight that is less than just the steering wheel of a normal car – is difficult beyond belief.

Ackermann and bump steer? If it’s in a typical car textbook, in this class of vehicle it’s usually not the solution…

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I thought that the idea that car wheels just went up and down over bumps, and were steered only when the driver turned the steering wheel, was pretty passé.

Passive ‘steer’ systems have been in production cars for many years, normally of the rear end.

In broad brush strokes, the systems work like this: The rear bushes are set with differing stiffnesses in different planes, such that when the wheel is subjected to a lateral force (as it is in cornering), it no longer remains parallel with the car’s long axis – that is, it steers.

For example, rear wheel compliance steer is often set to give toe-in, thus settling the cornering car.

The original Mazda MX5 / Miata had such a system. (It’s worth pointing out that the MX5 is generally regarded as one of the best handling, relatively cheap, cars ever released.) In their 1989 book MX-5 – the rebirth of the sports car in the new Mazda MX5, Jack Yamaguchi and Jonathon Thompson write:

No Mazda rear suspension is complete without some form of self-correcting geometry, as have been seen in the fwd 323 and 626’s TTL (Twin Trapezoidal Links), the 929’s E-links and the RX-7’s complex DTSS. The MX-5 double wishbones are no exception, though to a lesser degree. The designers need not worry about camber changes; a recognized virtue of the unequal length A-arm suspension is the admirable ability to maintain the tires’ contact area true to the road surface, attaining a near-zero camber change.

So the chassis designers’ efforts were directed at obtaining a desired amount of toe-in attitude that improves vehicle stability in such maneuvers as spirited cornering and rapid lane changes. Toe-in was to be introduced when the suspension is subjected to lateral force, not to accelerative or braking force. They considered that the MX-5 with its configuration, weight and suspension, would have sound basic handling characteristics, and the lateral reaction would be all it would require to further enhance its vehicle dynamics.

The lower H arm’s wheel-side pivots, which carry the suspension upright, have rubber bushings of different elasticity rates. The rear pivot is on a firmer rubber bushing than the front. The front rubber bushing deforms more under load induced by lateral force, and introduces an appropriate amount of wheel toe-in, which is in the final production tune a fraction of a degree.

Pretty well all current front-wheel drive cars have some form of passive rear wheel steering. The Honda Jazz uses a tricky torsion beam rear axle in which, according to Honda, “the amount of roll steer and roll camber has been optimised to deliver steady handling”.

But even better, the company has released graphs showing the toe variation over suspension travel (note: travel, rather than lateral force), with the current model compared with the previous design. As can be clearly seen, in bump (as would occur to the outer wheel when cornering) the Jazz (especially the new model) has an increasing amount of toe-in. Also note the differing shape of the curves in rebound (droop).

And it’s not just the ostensibly non-steered end that uses toe variations built into the suspension design.

Several suspension textbooks that I have suggest that setting up the front, steering wheels for non-zero bump steer can be advantageous. Chassis Engineering by Herb Adams (incidentally, a very simple book much under-rated) states:

Exactly how much bump steer you need on your car is like most suspension settings—a compromise. It is common to set the bump steer so that the front wheels toe-out on a bump. This will make the car feel more stable, because the car will not turn any more than the driver asks.

To understand this effect, picture what would happen if your car had toe-in on bump. As the driver would start a turn, he would feed in a certain amount of steering angle. As the car built up g-forces, the chassis would roll and the outside suspension would compress in the bump direction. If the car had toe-in on bump, the front wheels would start to turn more than the driver asked and his turn radius would get tighter. This would require the driver to make a correction and upset the car’s smooth approach into the turn. The outside tire is considered in this analysis because it carries most of the weight in a turn.

Assuming that your car has the bump steer set so that there is toe-out in the bump direction, the next consideration is how much toe-out. If the car has too much toe-out in bump, the steering can become imprecise, because the suspension will tend to negate what the driver is doing with the steering wheel. Also, if there is too much bump steer, the car will dart around going down the straightaway. A reasonable amount of bump steer would be in the range of .010 to .020 per inch of suspension travel.

Fundamentals of Vehicle Dynamics by Thomas D Gillespie positively describes using roll steer, where the toe variation of the left-hand and right-hand wheel is in the same direction, to alter understeer and oversteer effects.

Even that most exotic of road cars, the McLaren F1, had designed-in passive steer.

Writing in an engineering paper released in 1993, SJ Randle wrote of the front suspension: “Lateral force steer…. was 0.15 degrees/g toe out under a load pushing the contact patch in towards the vehicle centreline. This is a mild understeer characteristic – precisely what we wanted.”

In the case of the rear suspension, “the net result being a mild oversteer characteristic (ie toe out under a force towards the car’s centreline) or around 0.2 degrees/g. We had hoped for an understeer of 0.1 degrees/g.”

Such passive steer suspension behaviour would become especially important in vehicles that, in order to achieve other design aims, have dynamic deficiencies. So for example, a very light car that is aerodynamically neutral in lift, and has a low aero drag, is likely to be susceptible to cross-winds. On bump the passive toe-in of the rear wheels, and toe-out of the front wheels, would help correct this yaw.

Note that adopting these techniques doesn’t require the actual mechanical complexity – or weight – of the suspension systems to change.

But of course it’s quite possible to over-do these effects. As indicated in the quotes above, we’re talking very small steer angle changes. You can’t even transfer the ideas from car to car: the current Honda Jazz steers fine; the Honda City (that apparently uses the Jazz rear suspension) has an unmistakeable, unhappy, ‘rear steer’ feel that is disconcerting on quick lane changes. 

But it seems to me that if you are building any bespoke vehicle and simply state point-blank that there should be no bump steer at the front, and no lateral compliance leading to toe changes at the back, you’re taking away a pretty important string from your bow.

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This week in AutoSpeed we start a new series that I’ve immodestly called the ‘Ultimate DIY Automotive Modification Kit’.

It’s not the sort of material that you’d find anywhere else but at AutoSpeed – and, perhaps for that reason, longstanding readers will have seen much of the content before.

What the series does is integrate the testing and modification techniques that over the years I’ve discovered  to work for all cars.

Yes, all cars.

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Today I was lucky enough to drive an interesting car.

A 2003 model AMG Mercedes Benz E55, it comes standard with a supercharged 5.4 litre, 3-valves-per-cylinder V8 boosted by a Lysholm compressor spinning at up to 23,000 rpm and pushing air through a water/air intercooler.

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Back here I covered how, when I first started to design my Air 150 recumbent trike , I spent a lot of time looking for the lightest possible springs.

I tried rubber springs (in torsion, shear and compression), carbon fibre, elastomers and others.

My initial desire was to use torsion bars, preferably made from spring steel. However, I gave up on doing this for a number of reasons – weight, stress level in the steel (best addressed by using multiple leaves, Volkswagen Beetle style), and the difficulty in fastening the ends of the bar without introducing even higher stresses.

And the Firestone air-springs I chose to use in the final design are still my pick for springs in ultra light-weight vehicles.

But the other day I came across a product that might have changed the situation. It’s a type of skateboard that uses two wheels, mounted in line. The two halves of the board can pivot relative to one another around a longitudinal axis, and the two wheels can rotate, castor style.

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Suspension design is great fun, and very challenging.

I am not talking about ‘design’ as in picking which upgrade kit to buy for your car, but much more fundamental aspects like developing a whole new suspension – anti-dive percentage, camber change, longitudinal and lateral virtual swing arm lengths… stuff like that.

I haven’t done it for a car but I have applied exactly the same concepts to human powered vehicles.

When I designed the double wishbone front end for my first recumbent trike, I struggled with setting the ground rules. Like the:

• Position of front upper wishbone mount
• Position of rear upper wishbone mount
• Position of front lower wishbone mount
• Position of rear lower wishbone mount
• Position of upper ball-joint
• Position of lower ball-joint

With each location defined in three planes, that’s 18 variables. Add to that wheel offset and diameter, and inner and outer steering tie rod positions, and you’re looking at 26 or more accurate dimensions needed before you can even start.

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In my hand right now I am holding a bolt.

More specifically, it’s an Allen-key bolt (sometimes called a ‘cap screw’) that’s 30mm long and 10mm in diameter. It uses a metric thread.

It’s a high tensile bolt, which means – in plain terms – that it’s bloody strong.

I’ve just stepped over to the digital scales – it weighs 28 grams.

Now the reason that the bolt was sitting on my desk is that a moment or two ago I took it out of my pocket. And the reason it was in my pocket is that I’ve just stepped in from my home workshop, after finishing for the evening.

I’ve been building ‘Chalky’, my recumbent, full suspension touring bike that I hope to be one of the best human-powered touring machines in the world. Best for me, anyway.

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The other day I made a purchase that can only be considered an amazing bargain.

I first saw the goods (and then bought them) on Australian eBay, but by going direct to the manufacturer’s site, you can get them even cheaper.

So what am I talking about? Hose clamps – no less than 150 of them!

For just AUD$64.90 you get 150 stainless steel hose clamps to suit hoses from 6mm to 60mm. The clamps are packaged in boxes and appear to be of good quality.

And not only that, but you also get a flexible drive screwdriver (complete with three different sized socket bits to suit the clamps), a travel mug and a carry bag!

The company claims the retail value to be $240 – and that sounds about right.

The $64.90 cost includes postage to anywhere in Australia, and mine came delivered in a good quality cardboard box.

The deal is ‘while stocks last’ so you’d better get in fast!

Go here for the details.

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Over the years I have built plenty of simple structures that I’ve wanted to be both light and strong.

Those structures vary from little brackets that might be holding something in the engine bay, to complete human-powered vehicles that I trust my life to.

In all cases, the starting point for the design is to consider the forces involved. How does the force of gravity act on the structure? What direction do braking loads act in, or short-term transient loads like suspension forces? Will this tube be placed in bending (not so good) or is it being subjected to compression (good) or extension (better)?

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