My Cut N Shut FF Ideas

Hello my fellow FF weirdos.

I’m Scott, here in Southern California.
I’ve read the old FF Web for years, and now this website, but I don’t know if I’ve ever posted before.
Anyway, see what you think about these ideas of mine, and please share your feedback.

I think the frame and swing arm of the Kawasaki Concours14 or the very similar ZX-14 may lend themselves very well to a FF conversion without frame modification, and perhaps using swing arm modifications.

This would certainly be no mild-mannered efficiency special, but a high-torque powerhouse brute.

The Concours14, and especially the ZX-14, have monster engines, ABS (more common on the Concours), and are fuel injected. The airbox is integrated into the monocoque frame. The ZX-14 is chain drive vs the Councours’ shaft drive. The ZX-14 is popular in drag racing, and therefore an extended swing arm up to 18 inches longer than stock is available. I think extending the Concours’ rear suspension links and driveshaft would be feasible, which would help avoid a rearward weight bias, and the upper suspension links could be curved to allow a lower seat height.

In the illustrations below I think you can see the area between the frame and rear wheel might make a good place for the rider’s butt to sit, with the rider’s legs alongside the engine. The rear spars of the frame are about 13 inches wide where the rider’s legs would go around them.

The illustration with the extended swing arm shows a swing arm 10 inch longer than stock, and a seat height of about 18-19 inches.

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No shit!

Certainly looks feasible. I'd try had to get the wheelbase as short as possible, to make low speed maouverablity easier, and focus on maximum stiffness in the steering/front suspesnion (maybe use 'coupled' links for the steering rather than just one. It'll make a big difference to stiffness). I think you'll need to sit a bit more upright too, at least the upper body, it will need a bit of wrestling with the steering at low speed. But yeah. Go for it. It should be fast enough and I'm sure Malcolm Newell would approve.

That's am interesting take on 'torque free' shaft drive rear suspension. Should avoid the 'dutch roll' problem experienced by most 'simple' shaft drives (eg. Guzzi 850 etc.) but I wonder about torsional and directional stiffness, Maybe look at triangulation of the upper arms? Especially if lengthened. You wouldn't want to lack stiffness in that!

Is all that black stuff wrapped round the back of the motor chassis? Or just airbox? Be nice to get the fuel tank/battery etc. down as low as possible, and you'll need a bit of air space between you and the motor so you don't cook. Packaging everything into a new layout will be a challenge. Don't overlook the width behind your seat, Quite a lot of space there, not usually used by motorcycles

Hi Royce!

Thanks for your input!
I’m not sure what you mean by using coupled links for maximum stiffness in the front steering. Do you mean doubling up on any linkage I add, like if I add a remote handlebar?
I think that would be wise, too.
As for the rear suspension linkage, the lower link is pretty much a standard swing arm that spans left to right. If I were to lengthen the rear suspension, I think replacing that swing arm with a longer version would be wisest. I think you have a good point about similarly combining the upper left and right links.
The airbox is contained inside the monocoque frame, so a fuel tank would have to be added elsewhere. Behind the rider is my best guess for that, too.

Scott

Coupled

Ref, Twin links on a remote handlebar, yes exactly that. Stiffness, lack of flex in the steering is really important. The Voyagers all use a steering column, connecting a UJ on the transverse arm (that carries the chassis mounted ends of the (coupled)track rods) to the actual hand control yoke. It's 250mm of 25mm x 2mm wall thickness seamless tube. Pretty butch. Yet when I eliminated this feature in later designs, so the steering yoke mounts directly onto the transverse arm, the improvement in steering stiffness, and hence precision, was apparant immediatley,at walking pace.

A problem with this "Sit at the back" layout, common to cut'n shuts is that the lump in front of the rider can feel a bit disconnected. "Like steering a motorboat from the water skiis you're riding behind it" in an extreme case. Stiff, precise steering is an antidote.

I think there's a connection between how well rider is located and how stiff the vehicle needs to be for good feel and precision. Sit on top of the motorised bicycle and it can be surprisingly floppy - a lack of stiffness in the whole package. Bolt the driver in (F.1 style) and anything other than total stiffness feel horrid. FF's are somewhere in between, but the rider is much better located than a motorised bicycle and the FF needs to be much stiffer accordingly.

You're probably right about the fuel tank. Sit on it if you can, then it'll feel the same full or empty. The Voyager passengers sit on the fuel tank, right behind the rider. but I had to split the radiators and batteries to get them off the centre line where there wasn't room. Not ideal, caused a lot of difficulties. You're sorted with the existing radiator but it's worth sticking to a single battery if you can. Packaging is key, you have to get the same amount of vehicle stuff in less space.

Thanks!

Thanks Royce!
That all sounds great to me.

Scott

Doubling up links

If you're keeping the Kawa front end and using a secondary steering head, I recommend to NOT add a play-free connected second link. This is very bad engineering practice because it WILL cause stiffness in the steering. If you're concerned with redundancy, add a second link with enough free play to prevent binding. It's virtually impossible without an extremely stiff (read heavy) structure and higher precision than your bearings to set the handlebar axis close enough to parallel to avoid this if both links are tight. You could also make the handlebar axis somewhat flexible, but I think this is a bad solution. The redundant link would only come into play should the main link fail.

A substantial link from the handlebar to the forks has to take the maximum force your hand can apply. Not that much, really. And this usually only when pushing the bike around walking beside it.

I've ridden FFs with tele forks where a spherical rod end joint in a secondary steering head link was worn. When riding, the free play is undetectable. On the other hand, stiffness in a joint is detectable.

Arthur.

Extended swing arm

Why do you need to extend the swing arm this far? Pillion capacity? Why not keep the fuel in a tank over the engine? Knee room? Mass distribution? Where is the standard fuel tank in the Kawa?

coupling

Sorry but I disagree. I've run coupled drag links on Voyagers/prototype/Difazio for decades, using 3/8" rod ends or Metro track rod ends with no problems with binding. Free play can be eliminated by adjusting the track rods against each other. I don't personally find free play in steering acceptable. I run the pivot angle for the chassis end of the links at the same angle as the steering head (or upright, on HCS) at nominal ride hieght. (Slight variation in the HCS upright angle - rake - through the range of suspension movement, has no effect)

The issue is stiffness, as in lack of flex, in the steering, strength is easy. Any flex reduces precision in the steering, and a big, front mounted motor, makes precision important for good feel.

I do agree that the steering needs to be as free as possible from any binding, for self-steering (generated by the tyre contact patch moving off the centre-line as the bike rolls) to work properely. Coupling eliminates loads on the handlebar and other steering pivots and will always feel stiffer and more precise than a single link - even the bicycle people agree with this. Flex certainly noticable on Malcome's single link systems (Quasar/Phasar).

Coupling

Royce and I don't seem to be talking about the same thing. Free play in the steering itself is bad. The connection between the handlebar and a head stock mounted system (tele, LL, TL) as is being proposed in Scott's project is what I'm talking about. A single rod connecting the handlebars to the forks, properly designed, will be the best solution for feedback from head stock mounted steering. This has zero effect on "structural stiffness". For a redundant link to assist in stiffness, there must be added friction from the redundant link or compliance elsewhere in the system which is being controlled by this link. If coulomb damping is what is meant by increased stiffness (which I'm sure it isn't), then a redundant link will increase this or will be doing nothing at all.

The Quasar's Earle's fork is not structurally stiff so it's not surprising one can detect flex in it. Did Malcolm Newell use plastic lined ball joints with their inherently significant static friction (or are sloppy with free play and probably noticeable static friction as well)? All-metal ball joints have much lower static friction (but don't last as long when loaded). I expect one would get away with plastic lined ball joints in a redundant second link better than all metal joints because of their compliance, but this inevitably leads to poorer feedback. It's very likely that many bicycles and motorcycles with and without linkages have used poor engineering principles and bad design.

More.

Thanks, Arthur, for your ideas and advice.
I think I understand what you and Royce are each getting at, and I believe you both are making different points that both make sense.
The Concours and ZX14 both use a fuel talk in the standard position in the rider’s lap, but also extends below the seating surface, so using that stock piece would be unsuitable. A different fuel tank could be used in that same standard location, though. I think the stock frame and integrated airbox shape would be well suited to sit behind with perhaps a smoother, or even soft cover, though, so a fuel tank would go elsewhere.
I considered a longer swing arm in case the new FF rider position moved the weight bias too far rearward, and also to make room for a passenger.
I think the ultimate FF motorcycle design so far has been the Monotracer, and if I dream big, my ideal, no-limits creation would resemble something semi-enclosed and refined like that, with similar passenger seating behind the pilot.

Thanks for your input!
Scott

BMW R1100-1150-1200?

I’ve also put some thought into using a BMW R1100/1150/1200.
This would make a much more nimble, lithe, and lightweight result.
The modular construction of the R bikes would allow the rear subframe and suspension to be completely removed, while the front suspension remains.
I’ve stumbled across some custom DIY chopper builders using Harley Softail rear shocks slung under the engine for rear suspension, allowing the rider to sit just forward of where the rear shock would normally be.
These bikes were used by police here in California, making them easy and cheap to find, too.
I’ll add another illustration as soon as I figure how.

(No subject)

I just added another illustration of my ideas about a slightly different approach using the BMW.

Thanks.

Couples

"The difference between theory and practice is bigger in practice than it is in theory"

Arthur and I are talking about the same thing. The connection between the front wheel and the hand control.

In practice steering systems using a single link (eg Quasar, Phazar etc.) to connect the unsprung steered parts, either fork or upright (HCS) to the hand control, are observably more flexible than ones using coupled links. Even the 250mm Voyager steering column, stressed in torsion, produces detectable flex complared with the same system absent that column. By flex I mean any deflection between the wheel and the hand control. This is a matter of observation and experimentation. I haven't used couples in this system as a hobby, but to (successfully) eliminate flex and lack of precision in steering. Coupling the drag links eliminates resultant loads on the steering pivots and hence any flex at those locations.

This is quite apart from the massive flex usually found in fork type steering/suspension systems, eliminated by HCS.

Once free play and obvious flex is eliminated, the tiny, constrained, deflections acheived by using non-metal bearing joints (automotive etc.), or rubber suspension bushes (lower fork on HCS) are not observably detectable in direct comparison, in the same system, with all- metal joints and bearings. The tyre is itself flexible, the objective is to make the steering stiff (non-felxible) enough to be able to feel that tyre flex and the input loads that cause it, without other deflections, free play or binding, obscuring it.

But don't mind me, Do your own experiments, make your own observations. I don't really have anything more to add to this discussion.

BMW boxer option

The problem with this motor is that the cylinders get in the way of the 'foot down' position

Unsprung vs sprung and redundant links

The unsprung parts are the wheel, hub, etc. The handlebar on a head stock mounted steering system is sprung.

A structure to support a handlebar should be sufficiently stiff that any deflection from steering loads is not detectable. If a second link is required to counter deflection, then something in the supporting structure, either the handlebar axis or the top of the forks, is insufficiently stiff. This isn't anything to argue about; it's simple engineering.

My own extensive experience with my FFs equipped with tele forks and secondary steering heads confirms this. I can't speak for other builds as I'm not well enough acquainted with them.

Giant First Step Taken!

I now own the beast for my conversion!
I have added pictures on to the first post of this blog, of the bike as it is, and illustrations of what it could possibly look like in FF mode.
I found a GREAT deal on a 2008 Concours 14 and snatched it up.
I had never ridden one, this thing is no joke.
Fastest bike I’ve ever owned, by far.
A few modifications by the previous owner and it’s a little over 150 horsepower!
Very smooth, excellent suspension, fantastic brakes, and acceleration like some giant tightly-stretched rubber band is always ready to shoot you forward at any instant.
I’ve been riding it as it is, nonstop for the past few days. It’s an awesome machine.
If I can bring myself to tear it apart, the plan is to strip it down without any non-reversible modifications, and only temporarily make it able to be test ridden in the FF mode.
Then I can decide if I indeed want to permanently modify it into the machine of my FF dreams.
I have learned that in addition to the airbox and air filter, the battery of the Concours/ZX14 is inside the monocoque frame. How cool is that?

Scott

splendid

That thing will a rocketship... Good news about the battery, it's a big lump to package otherwise. You just need a fuel tank then. I see a seat height of 17.5", that's fairly high so you wouldn't want to raise it with a sit-on fuel tank. There should be plenty of room behins the seat(base). Don't miss the width available behind your seat, it's a big space. You're building a 'proof of concept' protoptype so it can run with a tiny tank to start with.

One thing you might want to consder is gearing. With stock gearing you'll probably run out of revs in top gear. This isn't going to be much of a problem due to the high terminal speeds involved but you might get easier cruising with a higher ratio - might be worth looking to see if there are other ratios in the model range. Given reasonable aero's 10% higher ratio seems to work.

Given the potential speed range, pushing towards 200 mph, aero's are going to be essential. I've ranted endlessly about this subject so I'll just suggest More Tail, Less Nose... It's a subject that wil reward study of modern vehicle aero's (Motorcycles are not a Modern Vehicle)in theory and practice. I'd go on, but I'm still learning about it it myself...

Thanks, Royce!

I hadn’t even considered the top speed of this thing. A stock 2008 Concours 14 tops out at 186mph(!!!) so I think that’ll be good enough for the foreseeable future. Easier freeway cruising at reduced rpm could certainly help attain better fuel economy, though, so that’s certainly a worthwhile consideration.
I am a aware that a shorter nose and longer tail would help aerodynamics, but the front-engined nature that comes with leaving the frame and swingarm stock makes a shorter nose, or larger forward half to make a more teardrop shape, impractical unless I enclose the rider inside the body. A longer tail would, I think, take away from the everyday practicality of the machine, and perhaps increase side wind sensitivity.
The more I ride this bike as it is, though, the more I love it!
That makes it hard to imagine tearing it apart.
To keep motivated to make such a big commitment, I’ll have to keep focused on my idea of what it would feel like to swoop through high-G corners, go from full lean in one direction to the other, and accelerate out of turns in a low to the ground, fighter pilot, feet first body position.

Thanks again,
Scott

Aero's

Not the dreaded Teardrop! Not Flying is your priority and the teardrop is a flight shape. I wrote a longish, possibly incomprehensible piece about aero's on this site at;-

http://bikeweb.com/node/246

But the 2010 Cmax shape, which has telescopic forks, would work at 200 mph and is good in cross winds and stuff, although I'd fill in the undertail area with a bit more 'fin' (The stock exhaust prevented this) FJ, also seen in that link, is obviously similar, but the tail tapers too sharply. 3-5 degree taper is the ideal. also now has better 60 degree windscreen taper. The front of the Cmax cockpit is rather blunt, imposed by the stock headlights. 60 degree taper is, again, the ideal. The Cmax 'pitot' style radiator intake works very well. Separation features are much more obvious on FJ.

http://bikeweb.com/image/tid/114

Don't think teardrop, think 'bullet' Snub-nosed bullet with a fin. It's side area, not length that needs to be bigger at the back. See how the top half of the Cmax 'Bullet' moves further back to the cockpit, moving the centre of pressure rearwards and reducing frontal side area. Note the airflow separation features alongside the nose - which is, in sideview,an inverted aerofoil.

Given that you're doing proof of concept with a reversible conversion you're really just looking at a seat and footboxes, a fuel tank and some bodywork. Make a list, work out the most difficult bit and do that first. I can also advise on sucking eggs...