I’ve written before about the fundamental challenge of human-powered vehicles – whether they’re conventional bicycles or unconventional recumbent two or three wheel machines. And what is that challenge? It’s the limited amount of power available to push the vehicle along.

Everything about the machine needs to be designed to operate within this finite power paradigm.

Unlike say a car, where the answer to bad design is to simply add more power to propel the extra weight or overcome the extra aerodynamic drag, on a bike you cannot take that easy route. Thus a bike is the most efficient means of transport ever developed. That is, it uses less power to move you than any other approach – even walking.

Part of that development has been the engineering of efficient gear systems. Unlike in a car, where rear wheel dyno figures often show a 30 per cent power loss between the flywheel and the road (that power loss made up of inefficiencies in the gearbox and differential, and the flexing of the tyre over what is usually a pair of small diameter rollers), in a bike the gearing system losses can be measured at being less than a few per cent. That is, often 98 or 99 per cent of the rider’s power is transmitted to the back wheel. And with the use of relatively large diameter wheels and high pressure tyres, the amount of power transmitted to the road is scarcely less.

All bikes use at least one system of gearing – that created by the different sizes of the front and rear chain cogs. But most bikes use a more sophisticated system than this – variable gearing, achieved by either an internally geared rear hub (eg a 3-speed hub) or derailleur gearing, where the chain is forced to move to a different sized front or rear cog. Derailleur gear systems are more efficient than planetary-based internally geared hubs.

Recently, I read a brilliant engineering book on bicycle gearing. Called The Dancing Chain, it is subtitled: History and Development of the Derailleur Bicycle. However, it is much more than that, covering gearing systems from the very first bicycles to current machines.

Written by mechanical engineer Frank J Berto, the large and detailed book (more than 1000 diagrams over its 400 pages!) reflects the author’s 35+ years of writing about bicycle gearing and a clear life-long interest in bicycles in general.

I found it a fascinating read, able to be perused on all sorts of levels – from reading it as a technical history of a specific engineering innovation, right through to gaining practical advice for current cyclists.

Despite being the ‘updated and expanded’ edition, the book has several major typos and in part needs better editing. It’s also not cheap – but I highly recommend it.

The Dancing Chain, History and Development of the Derailleur Bicycle, Frank J Berto (and contributing authors), 2009, ISBN 978-1-892495-59-4

(The Dancing Chain was purchased for this review)

And if you’re interested in bicycle design, another book worth checking out is An Illustrated Guide to The Cycle Zoo, a self-published book on alternative bike design by another mechanical engineer, Stephen Nurse.

A paperback of about 120 pages, the book covers alternative bikes that arguably can give much better on-road results than traditional upright, diamond-framed machines – recumbent bikes, trikes and tandems.

Read the book as a detailed guide to these machines and it can be a bit frustrating, but read the book as a sourcebook of ideas, information and diagrams and it’s much more satisfactory. Stephen is to be congratulated for writing and publishing a book on a topic so seldom covered, but for anyone heavily into these machines the book will be a bit simple, and for anyone just wanting to learn about what these types of bikes can do for them, the book assumes a bit too much knowledge!

But if for example you’ve read in AutoSpeed about our recumbent pedal trike designs and would like to learn a bit more about these alternative forms of human-powered machines, it’s worth a read.

An Illustrated Guide to the Cycle Zoo, Stephen Nurse, 2009, ISBN 978-1-921488-08-5

(The Cycle Zoo was supplied by the author free of charge.)

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One of the most interesting aspects of getting older is watching one’s internal values change.

It’s complex: some values simply solidify (you know, the more things change, the more they stay the same), but I’m sure that others actually alter. Perhaps as one sees more of Life, the more one becomes confident in taking value-laden positions.

A young person’s “I think maybe I feel this way – but I am not sure, no-one else seems to feel that way,” becomes an older person’s “Hell, everyone else is mad!”

I can clearly remember when I was prepared to sacrifice an incredible proportion of my salary so that I could drive a very fast car; now – despite no less liking driving very fast cars – I wouldn’t dream of spending nearly such a high proportion of my income on such a vehicle. And no, that’s not because my loved one would strenuously object, or because the demands of middle age (I am 46, so arithmetically probably past middle age) mean that money must absolutely be spent on something else like school fees or very small soccer boots.

As I write this it is ANZAC day, the day that Australians and New Zealanders remember a time in which men in World War 1 died in a particular battle. I am about as pacifist as it is possible to be when no war has remotely threatened my existence, but I certainly recognise that those men chose (note: ‘chose’) to fight to – in part – maintain the quality of existence I take for granted.

And so today when my wife said that she was making a tiny, simple wreath, and when she said that late in the day when all the formal brouhaha was over, she was going to pedal around to the local WWI memorial with our 5-year-old son Alexander, and when she said that she was going to lay the wreath in an utterly private, no-ceremony ceremony, I thought again about my values.

It’s almost too pat to segue into my next idea, but when Alexander returned from his wreath-laying trip, he said:  “And ours was the only home-made wreath on the memorial!”

And what’s that next idea? It’s this: I feel an increasing repugnance at the madness of our consumerist economy.  I mean, isn’t it patently obvious to even the biggest imbecile that constant economic expansion, in an economy underpinned by finite resources, can have only one ending?

I agree it’s a bit rich writing in an automotive web magazine that consumerism is crazy – when, since the 1950s, the car manufacturing industry has been one of the poster villains of those who think we should be greener and conserve the resources we have.

But perhaps that’s part of what I meant by the solidification of internal values: no longer do I agree that because (nearly) everyone says so, it must be the case.

Apart from the small, personal ANZAC ceremony, the other thing that made me think of these ideas is that today Alexander and I visited the local rubbish tip. We do it about weekly – and I have decided that it’s the very best quality time I spend with my son.

I think it is better than reading bedtime stories, better than birthday parties, better than tickling or playing chasey around the house. It’s better because it’s a personal and close (in that potentially dangerous environment, I hold his hand the whole time), and it’s also a challenging and intellectual experience.

Huh? Challenging and intellectual? At the local rubbish tip?

Yes it is, because the whole time we’re wandering round, we’re wracking our brains to come up with great uses for all the fantastic parts we see discarded.

“Hey Daddy,” says Alexander, “Look at this spring!” 

 “What’s this thing? Can’t we use it?”

“Oooh look, a bearing!”

“We can use that can’t we Daddy?”

And often we can, and often we grab it, the dump supervisor turning a tolerant blind eye to the ‘no scavenging’ and ‘children must stay in car’ signs.

I absolutely and emphatically don’t reject all aspects of our consumerist culture; the Web, for example, I regard as the most exciting and potentially most emancipating invention of my lifetime. Even if I chose to reject many other aspects of our culture (eg by living by barter alone) I would utterly want the Web.

But our current  disregard for the economic, social and environmental costs of all those goods we happily throw away every day strikes me deep inside as simply madness.

When I was a kid I read the science fiction yarn ‘The Year of the Angry Rabbit’. The main plot doesn’t matter here; what sticks in my mind is the vision of industry rapidly manufacturing expensive goods that when completed, were dragged out to the end of a jetty to be pushed into the sea – so that the industry could again begin making those goods. Full employment, a booming manufacturing sector – you get the idea.

So today at the dump when I saw late model TVs in a pile of as big as a few rooms in a (Mc)mansion I feel angst – you can be sure that most of the TVs work fine. 

And when I see on eBay a AUD$15.51 Sony 76cm CRT TV that has “absolutely nothing wrong with it and has a perfect picture” but must go because “we just purchased a new TV” I deeply wonder about a society that will waste such resources for utterly tenuous – and ultimately trivial – ideas like a tiny bit of extra screen quality or a having a somewhat smaller footprint in your lounge room.

People – even those naive and ignorant of what was to come – but who were prepared to die  defending a social order which today we (largely) enjoy…one can feel only respect.

But for those who have become so indulgently soft, spoilt and simply incredibly wealthy that they discard perfectly good working goods to a place that tramples them underground with a bulldozer, well, you gotta bloody wonder about them…

The ability of a wheel to move backwards when it hits a bump is a very important ingredient in gaining good ride quality. The movement is accomplished in car suspension systems by the use of rubber bushes; many have asymmetrical voids within them to allow this type of tiny backwards movement without adversely impacting on bush stiffness in other directions.

But what about in a machine that requires suspension pivot points that can’t cater for this movement, ie those that need non-flexible pivots?

In a two wheel machine, especially one that is very light in weight, a leading arm suspension can be designed that will achieve this.

Leading arm suspension systems have been used in commercially produced motorcycles (eg the Earles forks) utilised by BMW in the 1950s, and shown here.  Note that the springs/dampers do not locate the suspension in any way, instead, the leading arms (green arrow) are pivoted at the point shown by the red arrow. The “forks” are indicated by the blue arrow and the springs/dampers by the black arrow.

A leading arm design of this type has anti-dive under brakes built in; as the braked wheel tries to keep turning, it pushes up on the pivot point, so counteracting the weight transfer forwards. In fact, some Earles machines are known to rise at the front under brakes.

But how does this front suspension design allow a movement backwards when the wheel hits a bump? As shown in the BMW design, it doesn’t – or at least, not much.

But as shown in the design of this bike, it does. Again the green arrow points to the leading arms, the red arrow to the pivot point, the blue arrow to the spring/damper and the black arrow to the forks. Note how the pivot point is low and so the wheel clearly moves backwards as it rises.

The bike is a Birdy folding machine and the front suspension travel is only about 15-20mm. I recently bought one and I am amazed at how well the front suspension works, especially given its minimal travel. It’s not effective over large bumps but it works brilliantly at removing vibration and harshness.

It’s also a particularly interesting design because in many suspension types, building-in anti-dive geometry actually causes the wheel to move forward as it moves upward, so making bump absorption worse rather than better. That’s not the case with this design.

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Regular readers will know that I like riding pedal-powered machines (conventional bikes, folding bikes and recumbent trikes) and that I very often ride at night.

Over the years I have developed my own high-powered LED head- and tail-lights, stories that have been covered in AutoSpeed. (For example, see the series starting here.)

However, in technology nothing stays the same and so about a year ago I started closely checking out the new wave of LED headlights designed primarily for mountain bike use. Living near Canberra, perhaps the Australian home of serious mountain bikers, I soon discovered shops selling LED lighting systems costing anywhere up to AUD$500. These typically used multiple 3W and 5W LEDs, lithium battery packs and trick circuitry to maintain light brightness and protect the batteries from full discharge. Different flash and power modes are also available.

In the shop these lights looked excellent, and attending a 24 hour mountain bike race showed how effective these top-line lights are in real-world conditions.

But, hell, $500…

So I decided to take a punt on eBay, buying a light that uses three Cree LEDs in a cast alloy housing, a lithium-ion battery pack and a dedicated charger. All for about AUD$100 delivered.

First impressions were very favourable, and I mounted the light permanently on my Brompton. Riding out into country south-central New South Wales, where the roads have no lighting and quite often there’s no moonlight as well, I found the light excellent in reach, spread and beam pattern. In fact, have the headlight aimed even fractionally high and on these country roads oncoming drivers kept flashing their headlights at me!

But then things started going downhill. Firstly, I was out at night, and a fair way from home, when the light extinguished itself. No warning, no reduction in power – just from full brilliance to off. Luckily I also run a light on my helmet so I could turn that on and get home. The problem? The battery voltage was low and when this happens, the light simply switches off. OK, so charge the battery up again and monitor how many hours of light are available – about 3 hours in fact.

But then a few weeks later I found the same problem occurred – great light then, bang, nothing. And the ‘run’ time was getting shorter and shorter.

On that occasion I found the AA cells in my helmet-mounted light were also getting low, and in addition to the darkness, there was fog. It was a dangerous ride home.

During this time I was running a rear Cateye red flasher, in fact a AUD$50 tail-light with six large, high intensity LEDs. It’s a good tail-light but it has a problem common to many: it’s quite directional and so if not mounted exactly right, visibility to car drivers falls off rapidly. Plus, despite having eight different flash modes, none was all that effective.

Mulling over all of this, I decided to dig out my previous home-made lights and rig up a new lighting system. I wanted:

• Excellent front lighting – at least subjectively 75 per cent as good as the Cree x 3 system
• Much better rear lighting, with more range and vastly better off-axis brightness
• A great ‘run’ time
• Some indication that the battery was getting low in charge
• Little effort and no new cost outlay

So I dug out my front headlight, made from a stainless steel drinking cup, a 3W Luxeon LED and collimator, a heatsink and a 75mm magnifying glass. The tail-light I selected from my odds and ends box uses another stainless steel drinking cup, a lens salvaged from a camera, a red 1W Luxeon LED and another heatsink. (Both lights were covered in the previous series.)

I have a bunch of 12V Sealed Lead Acid batteries I’ve previously salvaged from discarded uninterruptible PC power supplies, and a home-made battery charger detailed here.

I added the Pulser  module and used simple ceramic resistors to regulate the LED currents.  I then added a diode and a handlebar-mounted switch so that I could easily operate the headlight in flashing or steady modes. The Pulser is set for a 3Hz flash rate with 12 per cent duty cycle.

It’s a relatively simple system that is also heavier than the professional approaches. But it’s also a system that has heaps of duration (something like 5 hours should be easily achieved, night after night if necessary), provides better overall safety than the previous system, and cost me nothing much to make. It also shows, by the very simple indicator of declining light output, when it needs to be recharged.

Kinda back to the future – something that on paper looks inferior but for me, works far better.

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I did an automotive electronic installation the other day. It’s a particular job I have done many times before – installing driving lights on a vehicle – but I came across a problem I’ve never before experienced.

After bolting a pair of Narva 175 driving lights onto the front of my wife’s Skoda Roomster, I decided to buy another pair for my own car. Simply, considering the cost of the Narvas, I was very impressed with the quality of the illumination upgrade on the Skoda. In addition to a relay, switch and terminals, the Narva package contains both wide and narrow beam lights; I found the effective combination of spread and penetration makes a huge difference to night-time driving safety. 

And not just safety – I’ve done a few long distance drives in the Narva-equipped Skoda and it’s a lot les fatiguing driving with good lights.

On my Honda the installation was always going to be relatively difficult. As with many cars, the Insight has no real mounting spots for additional lights. The approach taken by many – install an adaptor held in place with the number plate screws – didn’t do a lot for me so I searched on the car for places where brackets could be mounted. In the end I welded together a square tube assembly that sits just in front of the radiator but behind the bumper, held in place with welded-in spacers and bolts that pass through original sheet metal holes. The lights themselves mount on 10mm threaded rod through thick flat steel brackets brazed to the square cross-tube.

I also took some pains with the wiring, choosing not to use the relatively thin wire provided with the kit. Instead I ran thick, dual-core cable from each of the lights back to the Narva-supplied relay that I mounted on a new bracket located close to the battery. I added a 20 amp blade fuse in a holder and triggered the relay from the high beam headlights.

Being a slow worker and taking my time, it took about a full day.

That night, I went out to aim the lights. Driving around the country town in which I live there are plenty of dark streets and country roads to use – things were going smoothly until I suddenly found a major problem. After the driving lights had been switched on for a few minutes, they wouldn’t turn off! I had to actually pull over, lift the bonnet and physically tap the relay to get the lights to extinguish.

That made me unpopular with oncoming traffic and so after this had occurred a few times I gave it up and went home.

The next day I measured the voltage across the relay’s coil’s contacts. Relays disengage at a much lower voltage than they pull-in (for example, a 12V nominal relay might not disengage until the voltage has dropped to 3V) and I wondered if there was a residual voltage keeping the relay engaged. However, a check showed that while there was a voltage on the wire (even with the high beams off), it amounted to only 0.3V – and any 12V relay should be turned off at only 0.3V!

So what was going on? I swapped the Narva relay for another relay I had in my spare parts drawer and the new relay operated without any sticking problems. So the original relay was the issue.

I then pulled open the Narva relay to find that, on the contacts, there was a tiny but obvious burn mark (arrowed). The relay contacts, despite being quite large in area (as befits a 30 amp relay) were in fact touching at only a tiny spot. The contacts were literally welding themselves together!

That’s pretty weak in a brand-name driving light kit. So while I still admire the light output, I think if I fit any more of these lights, I might supply my own relay…

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For these two days, I have an electric bike on test. The ‘test’ is ostensibly for me alone; a local dealer of electric bikes was offering a no-strings electric bike for a two day loan (“just give us plenty of feedback”) and I eagerly took up their offer.

The AUD$1399 bike is a Chinese-manufactured, purpose-built electric machine with seven Shimano derailleur gears, a 250 watt rear hub brushless motor, and a removable lithium-ion battery. The bike has a real-world range of well over 50 kilometres, the battery weighs about 5kg and takes five hours to recharge, and the control system allows twist-grip power-on-demand or you can set three different levels of assistance that kicks in whenever you pedal.

The electric system is quite effective but the bike itself is not so good. The front suspension forks offer plenty of stiction; I’ve seen them move only when subjected to at least 1g bumps. The wheelbase is long, the castor quite great – but, oddly, on loose surfaces you can easily provoke steering shimmy. The mechanical disc brakes growl and screech and grate, and I found the riding position rather uncomfortable. On the other hand, the carrier is well designed (it will take panniers without modification) and there are effective mudguards.

So what is the electric bike like in performance?

Firstly, the effect of the 250 watts is uncanny – compared to old fashioned electric bikes, the power is much stronger. I assume that’s because the hub motor has no losses in transmitting the torque to the tyre, but it may be that the power is actually greater than the stated figure. Set on Low, the power is obvious. On Medium the power is sufficient to propel you at 20 km/h, and on High the speed on the flat and without a headwind is 30 km/h. This is all with gentle pedalling – but rather than use this control, you can choose to not pedal and instead use the hand throttle (although I found this curiously unfulfilling).

My initial ride was out on a long country road, one that is largely flat but pocketed with small, sharp hills. It’s no use comparing the electric bike with and without the motor running – at 25kg, the electric bike outweighs any non-electric equivalent and so the comparison isn’t valid. Instead, you need to consider what another bike is like on this route.

Compared with the two pedal machines I’ve often ridden on this road (a Brompton folding bike and a self-built recumbent suspension trike) the electric machine was 50 to 100 percent faster – averaging a speed of something like 28 km/h. That was with my normal pedalling effort – the scenery simply flew past.

And up those short, steep hills? The electric bike was an amazingly three times as fast as my other machines, just rocketing up the hills with “where’s that hill?” nonchalance.

But after riding the bike for a few days, I didn’t want it. I ride for recreation, and so the pedalling effort is part of the enjoyment I get. Take that away, and a bike isn’t really a bike. However, for elderly people, or for those who do a daily commute (perhaps including some steep hills), an electric bike could both make the trip faster and allow it to be much longer.

Now, I wonder what this electric system would be like on a really good bike, or even a recumbent trike?

Switched on Cycles

AutoSpeed was launched way back in 1998 – a grand venture in what was then the near-new medium of the Web. 

Unlike many other contemporary modified car and car technology websites, AutoSpeed has always been a commercial enterprise – paying staff members to not only prepare editorial content (words and pics) but also for layout and web hosting.

Over the 12 years, we’ve used a variety of financial models: from generating income by advertising revenue alone, through to paid member subscriptions – and then back to advertising revenue.

And of course, over that time the Web has also changed enormously.

Once, the idea of paying for content was seen (by some) as ludicrous – in fact, wasn’t it the whole idea of the Web that things should be available free? But over time, the idea that quality content doesn’t cost anything to produce has come to be realised as the mirage it is. Someone has to pay… and the revenue generated by web advertising alone is very unlikely to be sufficient to generate good content.

So what’s this about a cost to generate content? If you want good writers and photographers to produce quality material over a long period, they need to be paid. To put this another way, if those people are competent professionals, they’ll be able to earn decent money elsewhere – so why would they do it for nothing?

In fact, taking an average over widely differing research costs, and word and pic counts, a typical new AutoSpeed article costs about AUD$500 to produce.

In recent times we’ve dropped new content from two new articles a week to one new article per fortnight. We’ve also been running more material from other published sources. The reason for this decrease in new content is simple – not enough revenue.

The corollary is also pretty straightforward – more revenue equals more new articles.

But let’s be clear. AutoSpeed is not about to disappear from your screens. Our advertising revenue pays for hosting costs, and our readership numbers remain very strong. This is no ‘save AutoSpeed’ campaign, where if you don’t make a donation we’re gone.

So what is this all about? Simple – if you chose to make a financial donation to AutoSpeed, we’ll be able to produce more new content. For example, we could return to the format of one new article per week – or even two new articles per week.

If you’ve enjoyed AutoSpeed for a long time, or even if you’ve more recently been attracted to reading our content, consider making a donation. The amount you donate is up to you – but you can be sure that money will go directly to producing new content.

Go here to contribute.

Recently I read Thrust, the book by Richard Noble on his life in breaking land speed records, culminating in the development of the ThrustSSC car – the current world land speed record holder. The record was achieved in 1997.

The book is outstanding on a number of levels, including its honesty and clarity. The section where driver Any Green describes his techniques for steering the car is just amazing, as is the constant battle for funds that occurred every day of the project.

But one small part of the book particularly interested me: the section where the primary designer Ron Ayers describes how he went about designing the car.

The text is reproduced here:

How do you start designing a vehicle that is totally unique? Here are the characteristics of the problem that faced us:

1. By travelling supersonically on land we would be exploring a region where no-one had ventured, where even the problems could only be guessed at, so there were no known solutions.

2. As the aerodynamic forces involved were so enormous, any accident was likely to be fatal.

3. The project would always be underfunded, short of people and time.

4. There would be only one chance. The final car was also the first prototype. The first lines drawn on paper could well be the ones that are made. The very first assumptions and decisions, if incorrect, could put the project on the wrong track and there would be no chance of starting again.

Problem: how do you make those crucial first decisions when so much is uncertain?

First, every decision had to be a robust one. That meant it couldn’t be invalidated by subsequent decisions.

Second, we could only use technology we were very confident with. This militated against using the very latest technology in some cases.

Third, although direct experience of supersonic travel on land did not exist, we consulted widely, with aviation and automobile experts in industry, universities and research establishments. Experience with Thrust2 was invaluable, particularly in pinpoint¬ing practical and environmental problems that might otherwise be overlooked.

Fourth, where possible we left room for adjust¬ment or change, so we could incorporate knowledge acquired subsequently. Nothing was “hard wired”. One reason for using a steel chassis was that it could be modified if necessary.

Fifth, we didn’t try too hard to integrate the systems. If we needed to change one of them, we didn’t want to be forced to change them all.

Sixth, our choice of a twin-engined car made the design massively overpowered. Thus weight was not a critical factor.

The design resulting from such an approach must necessarily be “sub-optimum”. A second attempt, incorporating the lessons learned, would undoubtedly be better. But the design was proved in practice, and there was little about the basic concept that would need to be changed.

The more you read those notes, the more you realise the clarity of thought being employed: it’s also food for thought for anyone building a unique design of anything.

Noble and Green are currently involved with another land speed record car bid – the Bloodhound SSC.

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The trouble with suspension roll centres is that they’re often rather obscure in concept, let alone in location.

In this article I tried to simplify the concept of roll centres, largely by using geometric drawings.

(So what actually is a roll centre? It’s the imaginary point about which the car rolls. The front and rear suspension roll centres can be at different heights above the ground [but always on the centreline of the car] and on different vehicles the heights can vary from being above the ground, to at ground level, to below the ground.)

Normally roll centres are located by careful drawings of the suspension, a prerequisite being that you need to know the exact location of suspension pivot points, lengths of suspension arms and so on.

However, as shown in this diagram, the roll centre of an existing vehicle can be located by directly measuring the way the car behaves. If the car is physically rolled from side to side, there will be one point that never moves (or moves only minimally). That’s the roll centre. If multiple photos are taken of the car in end-view, this point can be easily located. 

This is a very useful technique – you can locate the roll centres for either the front or rear suspension, and no difficult measurements of the suspension geometry need be made.

And it’s not just the roll centre(s) that can be located in this way. In addition to roll, cars pitch – that is, the front dives and the rear rises, or vice versa. This occurs not only under acceleration and braking, but also over bumps in the road. The amount of pitch – or, more precisely, the pitch accelerations – are a major determinant of ride quality.

So how do you find the pitch centre? A book I have – Fundamentals of Vehicle Dynamics by Thomas Gillespie – devotes a number of pages of mathematics to locating the pitch centre of a car. However, as with the roll centre, pitch centres can be found by direct measurement.

I did this the other day for my recumbent, pedal, suspension trike. I am doing a lot of work on its suspension, including measuring real-time pitch accelerations over bumpy surfaces. After making a host of measurements of these accelerations, I thought I should find where the pitch centre actually is.

I had two photos taken of the trike (with me on it), both in side view. In one pic, the front suspension was at max extension and the rear in max compression. In the other pic, the suspension extensions were the other way around. (I use air suspension and for this test I interconnected the units front to back, so giving zero resistance to pitch. To get the front to adopt max compression, I added some weights.)

I then overlaid the pics, playing with the image until I could find a point around which the trike body was rotating in pitch. This was best shown by placing radii centred on that point – the circular lines intersect with the same part of the trike in both pitch extremes. (It’s harder to explain than it is to do!)

In this pic, the pink dot is the pitch centre. As can be seen, the greatest mass on the machine (that’s me) is located above the pitch centre. Furthermore, a lot of that mass is located a fair way from the pitch centre, increasing the pitch moment of inertia. This is one reason that over rough ground, the pitch accelerations of the machine are very low.

Talking about moments of inertia in pitch is taking it a further step in complexity. But back to ‘centres’ –  if you’re grappling with the suspension design of a custom vehicle, it make things a lot clearer when you can so easily locate not only the roll centres, but also the pitch centre.

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