Alligator build discussion

[beatr911]

Here is a bobbed Rebel 250. See all the space under the seat? I think the battery lives in the black area just ahead of the rear tire.

Also (to save posts) is a cycle ergo shot of my 6'1" self sitting on a Rebel 250 with the seat 17" above the ground. You can see that extending the swingarm several inches and pegs as far forward as possible may not be too bad.

[Michael Moore]

You'll have difficulty getting the seat height below 18" with a chain final drive. Remember that the chain rises as the rear suspension compresses, and you'll want some extra clearance above the top run for a slack chain to rise without sawing the rider's bottom apart. You could do two chains connecting to a jackshaft betwen the engine and rear wheel and lower things some more with a dropped engine but you have more parasitical losses. I did some Rhino3D drawings for a trackday FF based on a YZF250 thumpette with 58" wheelbase, Hossack FFE and the compound chain:



More details on that project (which is resting like a Monty Python parrot) at

Euro Spares - The YZ250F-FF Project

Here's a photo of a Gurney with a 426/450 Yamaha single engine in it that shows how they have a short intermediate chain running up from the dropped engine's countershaft sprocket:



Here's a photo of Tony Foale riding that bike:



56-58" is likely a minimum wheelbase if you try and keep the feet at or behind the front axle.

Airboxes make a big difference in how the bikes run -- think of all the bikes that had the airbox junked and "pod" filters put on, which never ran as good as stock. But if you've got a side-draft intake the airbox ends up behind the carbs pushing the rider back. The later BMW/Rotax 650 singles have a downdraft intake with the airbox (more) on top of the engine.

Singles and narrow parallel twins are about as far as you want to go with somewhat vertical cylinders. A Kawasaki 650 Ninja doesn't appear to be a "narrow" parallel twin. The problem is that there are very few engines out there that are FFriendly if you are doing a low-seat bike.

My current FF project is an SV325, a Suzuki SV650 less the rear cylinder head and with a faux "balance" piston substituted for the stock one to retain the 90 degree twin balance but eliminating the pumping losses/ring drag of a stock piston. Ditching the head reduces the height of the rear assembly by 6", eliminates running a hot exhaust header past the rider's crotch and lets the rider move forward.

I'd originally thought of using a TL1000 engine but it was easier to buy a running 650 than to get the rest of the parts for some partial TL engines that I bought. The TL has more power, but it is also significantly heavier/larger than the 650. HCS is also in the plan. Here's an early Alibre 3D model/mockup. This PDF is "active" -- if you click on the image and you have a late enough version of Adobe Reader you'll be able to zoom/pan/rotate:

http://www.eurospares.com/graphics/F...OnSV325big.pdf

Here's a CAD (cardboard-aided design) mockup of the SV325 engine/frame from a few days ago. The frame spar matches the top of the rear cylinder with a cap plate:



Here's an active PDF of the YZF250 model:

http://www.eurospares.com/graphics/FF/whole%20bike.pdf

You might find something of interest looking though this FF folder on my website:

Index of /graphics/FF

I will assure you that filling all of that underseat area formerly filled with airboxes, batteries, electrics, water catch tanks etc with the rider and eliminating the conventional fuel tank and looking for a new place to put all of the relocated stuff gets to be a real chore!

FWIW, I'm interested in FFs from a performance aspect, not fuel economy, and so my engine choices are different from what an ecomodder might look at. I want something with enough power and modern 17" sport tires so I can see how it stacks up to a conventional bike. With the SV325 I'm shooting for roughly 1/2 the power of a stock 650, which will put me at a 2-5 more than a stock EX250 makes. If I can end up with something that performs as well (or even better) as a stock EX250 I'll consider it a success.

I had twin-damper EX250 racer project



and the airbox/battery are in the way for a low seat bike (the photo shows CR carbs with open stacks, no airbox).

I don't know how the reliability/economy is of those 180cc Chinese Honda 90 clone engines is, but I'd look at an engine like that for an eco project because the form factor works a lot better for a low seat FF. Perhaps there's a 200cc scooter with a flat-single engine that could be used as a donor. I'm not up on what is available in scooters, but buying a complete and titled/registered bike as a donor has a lot going for it over piecing things together from parts.

I'd recommend avoiding "tiller" bars as you end up with bar motion a lot different from what you'd be used to. Instead, do a remote steering head with a drag link to the front end.

Many of the single-damper rear suspensions are going to intrude into the seat area, and reworking one of those designs to avoid that is not a trivial task. As mentioned above, convential twin rear dampers as used on the Gurney bikes avoids that, works fine (with good dampers) and frees up space under the seat (if you rework the swing arm) for a fuel tank or something else to go there.

The big scooters have a lot going for them as the engines are more in the right shape, but they tend to be low powered, heavy, may have problems getting high performance tires, and the scooter drivetrains are funky/clunky (IMO). But a 400 Burgman FF with a Hossack FFE and lower seat would end up much lower/smaller frontal area and might be easier for a (relatively) quick and easy project (for certain values of quick and easy).

I've never understood why the Gurney bikes didn't ditch the teleforks and steering head. AAR certainly has the ability to build something else. If nothing else I think they could benefit from a remote steering head to bring the bars back towards the rider. The one I sat on at the Chandler museum seemed like a long stretch to the bars that would have gotten old very quickly.

It is possible to do a Q&D "chop" of a bike, but I think you'll find that trying to do a nice/integrated design is going to take a LOT longer than you might think. There are a lot of factors to juggle before you reach a condition of Pareto optimality and then you've got to have the infrastructure/skills and/or money to actually get the thing built.

ETA: in case anyone is interested here's a good side view photo of the SV650 engine with a tape measure in it for scaling:

http://www.eurospares.com/graphics/S...Vmounts054.jpg

cheers,
Michael

[redyaris]

What I hope to achieve with the WR250R is a seat that in over 12" lower than the 36.6" stock seat height. This will result in a reduction of about 2 sq. ft of frontal area compaired to stock seat height. At this stage I am aiming at a seat height of 21" - 24" depending on the swing arm and chain movement. The swing arm extenson will be 6" - 8".

[redyaris]

The foot location and the space needed for the front wheel movement are a problem when attempting to get the seat as low as posible. The lower the seat the higher the feet are above the riders bum. I don't know how uncomfortable this can be for long rides because all the body weight of the rider is consintrated on the bum. The solution would seem to be a small front wheel or a very long wheel base. If the feet are moved forward to be beside the forks they need to be raised to avoid the front tire movement.

The area in front of the rider can/should be filled up as much as posible for aerodynamic reasons. The problem in this area is the space needed for steering...rider arms & handle bar movement.

The space behind the rider is constrained by the rear wheel/suspension movement. An interesting design aproach would be to start at the rear with the cargo space/boat tail and once you have the ...4 bags of groceries... accomidated you then move forward to the rider and seat height that will put the riders body in front of the the cargo space/boat tail. You may find that there is no need to lower the seat to the minimum.

[3-Wheeler]

Originally Posted by redyaris

The foot location and the space needed for the front wheel movement are a problem when attempting to get the seat as low as posible. The lower the seat the higher the feet are above the riders bum. I don't know how uncomfortable this can be for long rides because all the body weight of the rider is consintrated on the bum.....

Red,

I own a Honda Insight and know first hand that the seat/foot relationship is just about "flat", with the feet not much lower than the "bum" (butt).

So with a tape measure in hand, I just went out a measured as best I could the height difference between the two.

It appears to be about 6 inches give or take.

When I first purchased the car about three years ago, I spent about 1-1/2 months fiddling with the seat inclination, to arrive at a comfortable position for good under-leg support and well as the bum.

I would suspect that on a FF motorcycle, this same adjustability would prove to be important for good long distance travel.

So I'm not sure that the feet being at the same level as the seat would prove to be insurmountable from a comfort standpoint.

I would think that this seating position would immediately prove much more palatable than let's say the typical crouched-over-the-gas-tank riding position I perform now to save gas.

A funny side note: I have been using the "crouched over tank" technique now since 2007, and about two years ago, someone called the cops about a "cyclist maniac speeding on country roads". So here I come traveling at 40 mph down this very country road, when I spot a Sheriff down about 1/4 mile "gunning me" in the crouched position.

Needless to say, he had nothing on me and I crept past and scoped out the situation. About 1/4 mile past I decided to turn around and confirm my suspicion. He alluded, that sure enough someone had called in about me "blasting" on a high speed motorcycle at breakneck speeds. LOL!!!

Moral of story: A FF motorcycle would not attract as much attention!!!

Jim.

[Michael Moore]

Don't forget that for the rider position you also have to watch ground clearance. IIRC Alan Cathcart did a test drive on an Alligator and managed to drag a foot off of a peg in a corner, resulting in a broken ankle. When checking that everything on the bike fits into your required full-bump lean angles ensure that the rider will too.

The Yamaha 'gator above has the peg 3" or so below the axle, while many sport bikes will have them at axle height or above and they still need to have folding pegs for extreme cornering.

If you are talking about a slow-speed commuter then you can probably plan on a more upright position and lower pegs, but if you have to make an emergency hard-lean turn you don't want a peg levering the bike off the ground.

I think some recumbent push-bikes have very high pedal positions relative to the seat and some of those rack up a lot of miles. No doubt it is attention to all the details that will determine how comfortable any given position will be.

cheers,
Michael

[redyaris]

3-wheeler
You got me thinking... so the solution would involve how/where to distribute the load over as large an area as posible of the riders body. So the feet could be suported under the heel rather than on a foot peg under the ball of the foot, this would take half of the leg weight off the bum.
The seat would also need to be made as wide as posible and go as far under the thighs as the movement of the legs would allow. If the rider is able to be leaned back then the load bearing area would be increased, although the distance from the handle bars may not permit this unless a remote steering head is used.

Michael Moore
Good point about the ground clearance of the feet. This would suggest that a fairly high foot position is inevitable unless the feet are positioned close together.

[3-Wheeler]

Originally Posted by redyaris

3-wheeler
You got me thinking... so the solution would involve how/where to distribute the load over as large an area as posible of the riders body. So the feet could be suported under the heel rather than on a foot peg under the ball of the foot, this would take half of the leg weight off the bum.....

Red,

Yes, that's exactly what I had in mind as well.

The backs of the legs are supported as shown below, and a hinge at the rear and height adjustable in front.

The swing arm pivot could have been moved down as well, maybe allowing the seat to drop further.

That would have also negated the need for a second chain right behind the engine up to the swing arm pivot.



Jim.

[beatr911]

Great discussion! And Michael Moore, great detailed post! It's great to have several heads discussing this with efficiency in mind. Especially from those with experience.

The FFWeb seems to be much more performance oriented. I personally think that FF design could serve efficient designs best. I seem to recall that a high cg is desirable in a high performance bike for traction and lean angle reasons. But then again, I may be all wet.

Scooter power does have the packaging advantage, but shifter motorcycle power plants have the efficiency advantage as the CV belt turns power into heat. 250cc motorcycle engines have just enough power, are compact but a re-orientation of the intake may be in order to fit. Yes, the easiest solution is cone filters on the carbies, but a remote filter on the end of a long pipe bending immediately adjacent to the carb could bring the much needed airbox volume back.

The SV325 power plant has been a fascinating concept, one that may also be applied to a number of small bore cruisers (v-star/Virago650, Shadow 500/750, VLX 600, and others) with a similar effect. Obviously, significant frame modification is required to take full advantage of the engine reconfiguration.

As has been discussed, the onion keeps peeling, one thing leads to another and before long one has completely re-fabricated a unique bike from scratch. My original thought is to keep it as simple as possible by using a platform that is already close. Maybe that is not possible? I, personally, do not want to build a bike from scratch, but it is really really interesting to learn the problems and solutions from those that have.

[Michael Moore]

beatr911, the FF pioneers like Creasey and Newall saw it as a way to improve performance, economy, comfort and safety all at once. Lower the rider and reduce frontal area and economy and top speed (and acceleration from reduced drag) should all improve which is no news to the ecomodders.

There are several FF'd EX500s in Ireland and France, with the Irish one getting out for track day action:

http://bikeweb.com/files/images/PFGPZFF01.jpg

http://bikeweb.com/files/images/gpz400_ff_td_1-271.jpg

Arthur Middleton's GPZ400/500FF | FF Web

Arthur loaned his bike to one of the faster club racers who quite enjoyed riding it. You can see that his heels are above the front axle level. Look at the fairing and tail section that Arthur designed for his VFR500FF in the image album. That sees significant street miles (or kilometers).

Clearly, you can modify an existing bike (and on the Kawas above that's mostly extended swing arm, remote steering head and lowered seat and FF pegs). I figure that any motorcycle project worth doing is worth doing to excess so I want to build a complete new one and optimize (or at least fiddle with) everything that I can.

The SV325 is the closest modern equivelant to an Aermacchi/Guzzi/Motobi "flat" single that I could afford to build (I considered doing a Duc but that jumps the costs up, and I've had Ducs before and wanted to try something different), but it is a type of project that requires a lot of technical infrastructure.

Jim, running the swing arm as you've drawn in may have been avoided by the Gurneys because of poor squat/anti-squat chain geometry. I did a quick model with a steeply angled swing arm and matching sprocket and it seemed to have a lot of squat under acceleration. With an already low bike having significant pro-squat characteristics could be a problem. You'd also have to move the top damper mount forward to avoid a falling rate, and that would then intrude on the rider space.

The Gurneys all seem to be pretty tall (at least Dan is) and I think they designed their bikes for themselves. I'm 6' and the one I sat on was a long stretch to the bars, and you can see that Tony is having to lean forward off of the seat back on the Yamagator. He's several inches shorter than I am.

http://www.eurospares.com/graphics/F...gator2crop.jpg

I think Royce is not very tall and this photo shows where he thinks the Gurney handgrips should be:

Royce Creasey tries the Alligator, 2003 | FF Web

cheers,
Michael