Bob Walton's 160cc FF with very FFE

Bob Walton says: 'Basically, this is a twin shock rear suspension fitted to the front end with a big steering pivot through it.'
There is a 2 minute video of the machine being ridden on the road here:
Posted beneath the video is the following long explanation by Bob, which includes the key information:
'This bike weighs in at just 80 kg and does 80 mph with a 160 cc single cylinder engine'.

Now read on...
'This is a low weight, low drag, low centre of gravity concept bike. The low weight and drag give it better performance and fuel efficiency at the same time. And as I hoped to demonstrate in the video, the low C of G and the steering design make for excellent handling. There's nothing complicated here really. The big idea is literally just to put a conventional twin shock rear suspension on the front of this bike, mounted on a big steering pivot. But the bike is 2/3 the weight of anything comparable, it’s got 2/3 the drag, and it’s an absolute hoot to ride. For those who say "If it ain't broke, don't fix it", I say normal bikes are broke. They have the aerodynamics of a house brick. That dramatically reduces top speed and makes most bikes use as much fuel as a family car. And road bikes are much heavier than they need to be. The reason is simple. The handlebars are fitted to the top of the forks. That goes for telescopic and girder forks, Telelever and Hossack suspension and most trailing link and leading link designs. So the handlebars have to be at the front of the bike and quite high up. That means the sitting position is high up and usually upright with the wind blowing right at you. Once you've created a lot of drag like that, you probably want a bigger engine to overcome it, which adds weight and burns more fuel.

But here you can sit lower, with your legs stretched out in front of you, putting a smaller hole in the air as you travel, meaning less drag. And the handlebars can be positioned where they feel comfortable. Once you separate the handlebars from the steering you can have whatever geometry you want. This bike weighs in at just 80 kg and does 80 mph with a 160 cc single cylinder engine. Most normal 125 cc bikes weigh about 130 kg, like a Honda 125 for example. Another comparison is a Vespa 250. They have small wheels and about the same top speed. But they weigh 150 kg. Normally it costs a lot of money to get the weight of a vehicle down like this. But I haven't used any fancy materials or expensive components. Most of them were off-the-shelf- monkey bike parts.

An engineer called Tony Foale experimented with steering rake years ago on conventional bikes with telescopic forks. Each time he steepened the rake, the better the bike steered. The last experiment used a completely vertical steering head. But when he braked, he got an unholy judder. I went one step further. I went past vertical and actually made the rake negative. It steers lovely and there is no judder on the brakes. I've separated the steering from the suspension so there's no bump steer, and there's no chance of stiction in the forks because there's no forks. Hub centre steering designs like Difazio have limited steering lock or limited ground clearance at extreme lean angles, and complex steering linkages. But the steering lock here is about 45 degrees each way and there's good ground clearance too. The steering head leans backwards compared with a normal bike so it self- centres in a straight line and steers the same way you lean. If you sit on the bike at stand still, the steering naturally points forward. On a normal bike it tends to steer fully to one side ("wheel flop" it's called) so the trail needs to be bigger to compensate, but that makes the steering slower and heavier. Some choppers and scooters have quite a large rake so that the handlebars are further back for a more leisurely sitting position. But a large rake makes for excessive wheel flop and compromised handling.

Here the trail is just 5 cm but the bike is completely planted at any speed. You just couldn't use a trail anywhere near that on even the raciest of sports bikes using a normal set up. There's a pushrod on the front brake caliper to stop it going round with the wheel, which also gives it anti-dive. You can use up about four inches of the suspension travel when braking on a conventional bike, leaving only about one inch for actual suspension, and the wheelbase and the steering geometry change. You also get a sort of rocking horse motion when you stop. These are not good things. Also, you don't need dive to have 'feel' on the brakes. Ask any Formula 1 car driver. As for ergonomics, this bike's got roughly the same ride height and seating position as most cars, and I haven’t heard many car drivers complaining about that. I haven't crashed this bike yet, but I guess it’s better to hit inanimate objects feet first - and there's not far to fall if you drop it! So I am saying this bike is much lighter than anything comparable, and it’s got much less drag, the handling is sweet as a peach, it's dead simple and it's brilliant fun. There's some people that will never accept something that breaks the mould, but if you can't join 'em, beat 'em.'
see also:!AnrTeoVMhHXkm1yC84jb4MZcuBsQ!AnrTeoVMhHXkm0sIL5-vQ_nk_qiU

Bob Walton's 160cc FF with very FFE

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Which Publication?

Where did this photo appear, Bob?

Known space enlarged!

Thanks for putting this photo up. makes it quite clear. Definitely extends the envelope of two wheeler geometry! The trail looks pretty substantial - 60mm or so? and the "negative rake" (Not an ideal description but it'll do) will increase self-centering so the overall self-centering will be pretty strong. Does it self-steer at low speed? Sideways contact patch displacement, the primary force turning the wheel into a lean, will still occur but it'll be resisted by the geometry to a greater extent than I've seen in any other system.

I can see all sorts of problems with this layout, but really the question is 'what's the reason for doing it'? If it works like 'normal' steering goemetry it'll go some way towards showing that geometry, as opposed to mechanics, is somewhat irelevent, something also demonstrated by conventional HCS systems.

I'm surprised it doesn't dive under braking though. Both the trailing link system and the calliper mount seem to be pro-dive, or is there a torque link cunningly hidden behind the brake line?

Gosh, etc.

it was the Oxford Mail. Did

it was the Oxford Mail. Did you see the video? It's here

The trail is 5 or 6 cm now,

The trail is 5 or 6 cm now, but its adjustable. It tried about 3cm but it was too quick - very stable but too sensitive to a nudge on the handlebars. It self steers, but it still needs input at the handlebars at walking speed. But very tight, low speed corners are very easy to do. What sort of problems do you see? The reason for it was to improve the steering. It gets rid of wheel flop and gives quicker, stable steering. The steering is neutral on a normal bike above some particular speed. Below that speed wheel flop is a problem. Not so here.

But you finish up with a bike that weighs 80kg and goes 80 mph. There is a push rod on the brake caliper that pushes up on the front of the bike when you brake to counter dive. You can choose whatever angle you want to dial in whatever dive you want by adjusting the angle. I have given it just a smidgen. You have to cut and paste this in your web browser I think for the video There are some photos at the bottom of the write-up that show the anti-dive link. Hub centre designs normally have a jointed linkage between the front wheel and the handlebars to take out relative suspension movement. It's quite tricky to dial out bump steer. This just has a direct link to the wheel assembly.


OK, there Is a torque link on the brake calliper, so that's the braking dive dealt with. Anti dive is Very sensitive, just 10mm anti-dive on the Voyager HCS is slightly too much (Lower fork pivot 10mm above ball joint at wheel centre).

It's interesting that you run so much trail And negative rake but get light steering at low speed. I'm quite surprised the steering turns itself at all at lower speeds. The small wheel may have an impact on that. I run about 40mm trail with around 15 degrees of 'positive' rake on a 16x120/80 wheel to get light low speed steering and good self-steer, below about 30mm trail on that wheel the steering goes mushy at low speed and doesn't self steer well enough. Geometry isn't very significant in HCS and I've run between 25-60mm trail and 10 - 17 degrees of rake in development. I've aimed for 'unnoticable' as the target feel. (that's my general development target)

I guess my question marks are my usual bugbears. The suspension is steered, adding rotational inertia to the steering and energising any wobbles - HCS systems only steer the wheel, not the suspension. And the whole ensemble isn't very stiff in torsion, reducing control precision and allowing wobbles to develop. HCS is very stiff in torsion, wobbles do not occur and there is high and robust steering precision. An issue here is probably the weights of your FF and the Voyagers which come in at around 300Kgs wet and run up to about 120 mph. Quite a bit of force multiplication there.

Of course you could increase the torsional stiffness in development and use "suspended steering" that only steers the wheel. It would be difficult to use our 'double wishbone' HCS as a trailing link system for purely mechanical reasons, but you could use a Hossack system with negative rake on your existing structure. this would markedly reduce the rotational inertia.

So really it comes down the steering quality/stability of negative rake versus positive rake, once all the usual problems of motorcycle steering/suspension have been eliminated. I hope you find the space to continue to develop your concept!

no wobbles

You seem to assume I have a wobble. I don't. I don't need to increase the torsional stiffness or reduce the steering inertia by using a different design. If you look closely you will see that the shocks are quite close to the steering axis, just like with tellies. You are saying 'once all the usual problems...... have been eliminated', but I don't have any problems.

why did you ask?

Why did you ask about the photo?

Self steering

Great to see an original build. Excuse my ignorance, but as a non bike rider, what is meant by self steering?

Oxford Mail photo + Difazio Tank-slapping

Well, presumably there's an article accompanying the photo?! How about scanning that too? Also, while I'm on, it's not actually true to say that HCS steering never wobbles. The second Difazio CX500 FF known as 'The White Eleffant' could 'shake its head' viciously, and for no good reason, on occasion. I personally experienced it once while bimbling near the Elephant & Castle in London, curiously enough, but I certainly wasn't the only one. We used to call them 'tank slappers' except that the tank was under the seat in the Difazio FFs!

self steering


I took the 'self-steering' to mean that when the bike topples to the left it steers left which makes it sit upright again so the balance is corrected. I am sure someone will correct me if I am wrong.


oxford mail

Copy paste this into your browser but it doesn't say much. The following say a bit more, but some of the photos aren't that flattering to be honest. (Don't show them to anyone.)!AnrTeoVMhHXkjDf-puTLvS-DASz0!AnrTeoVMhHXkjDiPK5EiBOlmbEPP

There was a man from Yorkshire who contacted me recently with a CBX engine and the back end of a normal bike who was asking me for some photos of my front end so he could build one for himself and stick it on the front of his machine. I hope it works out for him.

I said what?

I assume that if you'd experienced any wobbles you'd mention it. I was noting that low torsional stiffness and high rotational inertia are the drivers of steering wobbles - and I make that connection because increasing stiffness and reducing inertia have been shown to eliminate wobbles.

As you don't experience wobbles, even though you use steered susepension and support the front end on a low-torsional stiffness beam, this must be either the result of some unsuspected advantage of negative rake. or that the mass involved, including the small wheel, and the long support beam just do not reach a suitable harmonic. Or some other effect. Obviously there are various experiments, some made possible by your contact with the CBX owner, that might throw light on this and allow further exploration of your concept.

I do not intend criticism of your design, or any feature of it. It's very interesting, throwing into doubt various 'well known facts' concerning two wheeler geometry, something I quite enjoy doing myself. It's perfectly possible that the additional self-centering provided by negative rake reduces the tendency to wobble and these are surely things that should be investigated, no?

If 'you don't experience any problems', using a system that, apart from the negative rake, does traditionally suffer from 'problems', then it is in everyones interests to determine why - by suitable experimentation. And I look forward to hearing more on this.

Wobbles and HCS

It's true that I've said that HCS doesn't wobble. This is because I'm referring to the sort of HCS desgined by Tony Foale, Bob Tait and myself, where the wheel is suported by a top wishbone. Specifially not systems where there is no top wishbone, early Difzio, Tessi and various copies designed by people who do not understand the need for torsional stiffness. The first Banana was the first Difasio system with a top wishbone capable of providing real stiffness and I was repsonsible for that. The second Difazio FF (white elephant) did not have a rigid top wishbone but reverted to the flimsy, non-straight item he'd used previously on some HCS units. Jack himself mentioned to me circumstances where he'd had his system go into a wobble.

That the Elephant wobbles is an elegant proof of the importance of teorsional stiffness. If anyone had bothered to mention this issue to me I could have speedily fixed it. And still can.

I continue to maintain that if anyone experiences a wobble (more than two cycles) on an HCS with a proper top wishbone they should stop and investigate. Something has broken or come loose. I base this on experience, not theory.


That's exactly right. Bob's video shows him riding 'hands off' proving that his system 'self-steers' This is the basic physical effect that makes two wheelers ridable. It's generated by the finite width of the contact patch. When the vehicle leans the centre of the contact patch moves towards the lean, away from the steering axis ground contact point. Rolling resistence then 'drags' the contact patch centre back in line with the steering axis, turning the wheel into the turn and correcting it. To hold a bike in a turn it's necessary to resist this self-correcting effect by applying steady pressure to the steering. Tyre width defines the effort required.

The effect is modified by tyre width and geometry. 'Positive' rake assists at low speed, Trail reduces the effect at high figures and at very low figures, but tyre width is the main determinant. Wide tyres, and fat contact patches maximise the effect.

Bob's system has a fat contact patch, increasing self-steering, relatively high trail, somewhat reducing it and 'negative' rake that might be expected to also reduce self-steering as the vehicle is lifted, rather than lowered, as the wheel steers. However 'geometry' has limited effect compared to tyre sidth, mainly affecting 'feel' and stability in traditional 'steered suspension' systems where the wheel has to largely look after itself.


I'd assumed that If I put an entry in directly under the entry I was replying to it would appear there. This doesn't appear to be the case. meaning this interesting mult-thread discussion will rapidly become incomprhensible. So it goes. Maybe there's another way?

geometry vs tyre width

I am sure the tyre width affects the steering, but I think the geometry is the overriding driver. I made some inline skateboards once with quite thin, hard tyres. The front wheel was a forward leaning caster (negative rake you might say). At standstill the front wheel would steer in proportion to the lean angle. But when moving this was modified by the caster effect which tries to keep the wheel pointing in the direction of travel, like the casters on the chair I am sitting on now. The net effect was that the skateboards were easy to ride (even without handlebars) and I guess the contact patch was tiny. If I had made the caster steering axis 'positive' (like a motorbike headset) I wouldn't have been able to ride the skateboard at all. I wanted to reproduce that effect with my bike, using a negative rake, and it seems fine. I think the principle is the same, but the geometry is the important thing.

See the video here:

One of the skateboards has fat tyres but it balanced just the same.

Skateboards are different to two wheelers!

I have to disagree with you. I'm talking about leaning wheels, skateboard wheels do not lean and both ends are steered mechanically by leaning the board. The geometry just defines how much steering angle you get for a given lean. Although the experience of skating is very similar to the experience of riding a two wheeler - they both 'feel' like single track vehicles and 'counter steering' is needed to initiate a turn - the actual dynamics of the two are quite different. It works to think of the pivot bolts as the contact patches of a single track vehicle, with the trucks doing the same steering job as the contact patches of a two wheeler, but using a different mechanical system. The rider is the rest of the vehicle...

(I was a skater for deveral decades until my joints wore out, included a stint as techncal editor of Skateboard magazine and member of their first 'test team')

Self-steering two wheelers rely on leaning to 'operate' the self-steering effect. It can be shown that rider movement has virtually no effect, unless they actually steer. Experimentation with different tyre widths easily demonstrates a consistent relationship between tyre width and what I call the "Stabilising effect" I described above, (using the same geometry). It's not something I made up in my head, it's the explanation that most completely describes the observed effects.

But don't mind me, everyone has their own theory as to how two wheelers work and you're welcome to yours! I get consistent and reliable rssults designing vehicles around my theory, so I'm happy. You don't have any problems with your set up, so you're happy. I'm not going to do endless discussion of what seems to me a simple mechanical relationship. My interest in FFs is seeking production manufacture of proven vehicles with hundreds of thousands of miles of development behind them. I applaud your project to reform understanding of two wheeler geometry and look forward to the result of your experimentation with interest. Pure research is always valuable.

Really I'm suggesting that you need to demonstrate that negative rake is the reason you 'don't have any problems' rather than anything else. But it is just a suggestion!

Sorry, misunderstood

I just realised they you probably mean a two-wheeled free-steering skateboard when you said 'in-line' skateboard, with circular section wheels. This obviously renders my comments about lean-steered four-wheeled boards irelevent. Apologies, Although the rest stands.

I'm somewhat baffled by your terminolgoy. Office chairs have massive trail, the steering axis usually leads the contact patch by at least half the wheel diameter, but has no castor/rake at all. (in my world 'Trail' is the amount the centre of the contact patch 'trails' the point where the steering axix meets the ground, and Castor or Rake is the angle to vertical of the steering axis). I'm interested to hear what actual geometry your skateboard has, particularly at the rear - but from a skater viewpoint, I doubt if rear wheel steering applies to PTW's.

Castor/Rake may affect the wheel position when leaned at a standtill but trail keeps the wheel in line when moving and contact patch width defines how much the wheel will turn into any lean - but only when rolling. Rolling resistance is the actuating force. Please feel free to make some free steering wheels with zero-width contact patches (sharp edges) and see how they self steer, on a hard surface. It's an easier experiment with skatewheels than pnuematic tyres! (I've only researched 90/90 through to 120/80 tyre widths).

Really I'm interested in what you believe the benefit of negative rake is. Obviously we all want to avoid the deficiencies of steered suspension, hence the painstaking development of HCS. Incorporating negative rake is somewhat tricky, although it can probably be done most tidily with HCS, allowing leading link suspension more directly connected to the main vehicle structure, but what beneift will be achieved compared to existing, in-use, systems that already avoid the problem of conventional motorised bicycle front suspension and steering?

following your comments...

I am using the same terminology as you for rake and trail. The rear wheel of the skateboard does not steer. I guess you didn't copy paste the link into your browser.

I don't agree that rolling resistance is really the 'actuating force' exactly. The caster on my skateboard, because of its lean angle, steers the way you lean even when it is not rolling, so there is no rolling resistance, but it still steers. The casters on my chair would point the way I pushed the chair whether they were square or round section or very thin - again the steering doesn't depend on the tyre shape. It's the geometry that counts (although tyre size and shape does have an effect)

The advantages of the negative rake are that you can get rid of wheel flop, you can have very quick and stable steering, and it's very simple. The design means the handlebars don't have to be high up and quite a long way forward so the sitting position can be low and streamline. I thought that was the main point of FF bikes. So although a negative rake is an inherent feature of the design, it is not the only feature that gives the overall design it's advantages.

In addition to the above, this system has specific advantages over hub centre steering. They are: that you don't need a complicated steering linkage to avoid bump steer. Lots of pivots and joints in the system can lead to vagueness (the 'mushiness' you were talking about earlier) and each bearing can wear with time developing play. Also the cost depends on the number of components. The other thing is that the design here simultaneously allows a 45 degree steering lock while not scraping the ground when cornering.

there's some detail photos here

O.K. Is it potatos. Or potatos?

There is some basic disagreement here in that I don't see any connection between the behaviour of rotating and non-rotating wheels- due to the absence of rolling resistance, and an office chair wheel doesn't lean - the 'stabilising effect' of contact patch width relies entirely on the reaction to lean. But really any discussion of the related effects of trail, rake and tyre width must rely on experimentation, one can hypothesise indefinitely.

I've only experimented within the parameters relevent to PTW's, reducing trail and rake from motorcycle settings that prove excessive on HCS equipped FFs to the point where self-steering stops working and similarly with tyres, running sections between barely acceptable load ratings and excessive stabilsing force levels. This has provided consistent results leading to the settings that I normally 'fit' to FFs and my understanding of these effects (such as it may be).

I am therefor interested in experiments outside these limits as they should increase understanding. A 'zero-width' contact patch experiment would be very interesting. and your negative rake experiment, following on from Tony Foales work is also interesting. It could be argued that what has been shown by the very wide variation in rake achieved by all researchers, is that rake has very little effect. unless it is excessive (e.g. 'choppers' etc.), except in marginal 'feel' quality. I do not make this argument, just watch with interest!

But your critique of HCS ("double wishbone" as in Difazio/Tait/Creasey/Saietta) is obsolete. The Voyager system has 38 degrees of lock each side, perfectly adequate on the 1575mm wheelbase Voyagers snd could be easily increased. There is no bump steer and the simple linkages use ordinary car joints (Metro) which cost a few pounds and last, in some cases, indefinitely. The shortest life item, the (MGF) balljoint in the wheel centre lasts for around 50,000 miles, costs less than £10 and can be changed without removing the wheel. The mush I mentioned was caused by a very short trail experiment - sub 25mm - where contact patch damping overwhelms the trail effect at walking speed. These systems have no inherent dive, low rotational inertia, very high torsional stiffness and a level of precision (or lack of vagueness...) unknown in motorised bicycle systems. They have demonstrated excellent crash performance and are unoticable in use. Unit cost is less than most telescopic assemblies. Importantly for FF use, the assembly needs only be about 50mm higher than the wheel itself. It is not possible to ground any part of the system. It's interesting how myths perpetuate(see "read this first").

Hopefully eveyone on this site agrees with your general remarks about the FF layout. It's why the site exists. Low frontal area is certainly one of the big advantages of the FF layout but the dynamic advantages of low CG and the control advantages of a secure seat are more central features. "Comfort, Handling, Safety and efficiency" I agree that the aerodynamics are the most challenging and interesting feature though. I hope to live long enough to get them right!

not just rake

This isn't just about the rake. This is a whole steering and suspension design - a whole machine, one aspect of which is the rake.

But regarding rake since it is an essential feature, when you say "any discussion of the related effects of trail, rake and tyre width must rely on experimentation", does building a whole motorbike from scratch and demonstrating it not count? Also, my in-line skateboard steers the way you lean it whether you are moving forward or not, with thin and fat tyres. I would call that proof positive. This is not a hypothesis. :)

But if you really want an experiment with a bike with wafer thin tyres, here it is:-

This isn't a hypothesis either. It's a working machine, and you can ride it no hands.

When you say you hope to get all the parameters right one day, are you saying that I haven't? :(