Alligator build discussion
 

The Dan Gurney Alligator was a limited run bike of about 30 units. He is a legendary man with a colorful racing history and serious design and fabrication skills, along with his team.

The Alligator concept strives to reduce horsepower requirements to go fast by reducing wind drag. If I remember right they did 140mph on about 70hp, not in a tuck. This efficiency concept obviously also applies to reducing fuel consumption.



I thought I'd start this thread to discuss how one would go about building a version of this bike except with fuel efficiency as a priority. Some key points to discuss could be:
-Ergonomics. Would you fit on it. Handlebar location could be an issue
-Suitable donor bikes.
-Swappable parts to donor bikes.
-Fabrication hurdles/solutions.
-Why or why not this is a stupid idea. Not IF it is.
-Fairing ideas.

Anyone interested?

Oh, I almost forgot. The thing that drives this is a LOW seat height to get out of the wind. I think it is about 17" above the ground. This corroborates desired values on the FFWeb discussions from those who've experimented and now know. Apparently the sweet spot is like 12"-17". But much lower than 17" runs into clearance issues with the swingarm with motorcycle wheels and adequate suspension travel.

First check your state laws on motorcycle seat height. Many states like NY require a 27 inch seat height for two wheelers and a 20 inches for trikes. There are some good designs on FF bikes on craigvetter.com

What I look for as a candidate for this type of bike is one that has a bolt on rear subframe so that I can try various versions without giving up the ability to return the bike to its original configuration. Both my WR250 and my KLR650 have bolt on rear subframes. I have purchased a used WR250 swing arm from ebay, that i will be extending after I have built a jig to hold all the peaces in place for welding.

You can't really tuck on a bike like this, can you ?
:D

I believe that Gators are ridden in the "pike" position...;)

That looks like a very comfortable rider postion with built in back support...:thumbup:

The only problem is no b i t c h seat. Which now that I think about it, may be a problem solver...;)

>

So building one of these will most likely require cutting, welding and fabbing the rear frame section, sacrificing the original bike. The bolt on rear subframe bikes like the WR will be exempt for the most part. To make room for the rider the swingarm probably will need extending at least 4", which is commonly done on a range of bikes so is probably not a big deal especially if working with steel vs. aluminum.

Ergonomics:
Humans need small bike cross sections directly in front of the crotch in order to fit without splaying knees out in the wind. When seated just above the swingarm the rear loop of the frame is directy in front of the rider. Perimeter style frames are widest at this point so it will require modification or a narrow section here.

Hands and feet when seated in a semi-reclined position typically require that the feet be forward of the hands to reduce knee angle and reduce reach to the bars. Forward foot controls and rearward handlebar placement is then desired. More fabbing to place foot placement as far forward as possible without interfering with the front wheel. Additionally, a "tiller" style bar to reduce reach.

Electrics: The battery on most bikes is directly under the seat. The open space between the (now forward) footpegs is a good relocation area. It also helps keep the center of gravity low.

Air box: This also is usually under the seat. Hmmm, maybe a short cone filter or piping the intake to another location will work.

Fuel tank: This is tougher if it is to be relocated. Leaving the donor bike tank in place keeps the CG high but may be worth it. Fabbing a tank to fit into the cavity created by the extended swing arm could be a solution also helping keep CG low.

Rear suspension: A single shock system is desirable as it is compact and doesn't require an especially strong rear subframe, easing fab requirements. Dual shock systems reduce swingarm loads, easing extension fab requirements and open up the center of the bike for other uses like a fuel tank, air box or battery.

Donor bikes I'm looking at are 250cc as they have outstanding MPG potential and really need aerodynamic drag reduction to do well at higher speeds. Cheap is also good, so finding a lightly damaged bike is a possible route.

250 Cruiser bikes already have a low seat height, small diameter wheels (lower swing arm height) are pretty common and cheap.

The Ninja 250 is really common, may be even cheaper but bars and frame mods may be more extensive. Attached are some pix of a mod started by an ecomodder that wasn't finished (search for it).

Here is a dualsport DR350 that was bobbed. The seat is low but rear wheel will hit the seat when fully compressed.

This sounds like something I would love to do on my sr185. it's already so narrow you wouldn't need to change that any, but the old school rear suspension would be a little tough to modify. I would think a 200cc single would be the perfect candidate, maybe a dual sport or converted dirtbike as they typically have the monoshock setup, and narrow profiles.

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.

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:

http://www.eurospares.com/graphics/y...ine3chaina.jpg

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:

http://www.eurospares.com/tfoale/200...Sprocketsa.jpg

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

http://www.eurospares.com/tfoale/200...ney_Foale4.jpg

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:

http://www.eurospares.com/graphics/F...5FFside014.jpg

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

http://www.eurospares.com/graphics/ex250/exts6.jpg

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

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".

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.
:confused::eek:

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.

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

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.:confused:

:thumbup:

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.

http://ecomodder.com/forum/attachmen...1&d=1347229590

Jim.

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.

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

Michael,

I thought about this as well, in that the change in swing-arm inclination *could* affect the amount of squat.

The same is true of shaft drive bikes, but this is another topic for discussion.

However, being that my intent with a FF design, is to get better mileage, then acceleration and the amount of rear squat is pretty much a moot point, within reason.

A side note, you probably still remember the ATAC sprocket that was sold for a few years, way back in the late 70's if memory serves. These sprockets were supposed to help with the topic you speak of, but then they disappeared. Maybe they did not *fix* a problem after all?? Who knows.

To get a rising-rate shock setup, I usually think of the shock top being inclinated at about 45deg or so from horizontal, not the almost upright position seen in the Yamaha above. From a purely technical standpoint, you are correct, but I'm not sure it would matter enough for a fuel sipper.

Jim.

Michael, Just curious. For the club racers that rode the FF, were the lap times comparable or did they at least feel the times could be comparable or better than thier regular bikes? Excuse me for this basic question but I just don't have a feel for the track performance other than it's enjoyable and fun.

I can see that using a 17" wheel is preferable for tire choice. The small cruisers use a 130/90-15 (~24" OD) tire which is about equal in OD to a 130/70-17 so that evens out with tire choice. I was hoping that the small cruiser 15" tires would be a height advantage, but this is not the case.


Any smaller and it's all scooter tire choices. Or heavy LRR 12" or 13" car tires only good for another ~1" lower swingarm pivot (2" smaller OD). Maybe not worth the tradeoff.

For a low power bike, lowering the swingarm pivot into pro-squat may not be a significant problem. Harleys (not that they have exemplary handling and ride) often have pro-squat swingarm geometry with much more torque. The handling performance envelope target for this bike would be at least as good as the Harley. Probably better.

Rereading, the Burgman 400 does look like a good prospect. It seems to have one of the most efficient transmissions of the scooters, being bathed in oil and such. Form factor is close. Searching, I have not been able to find one hacked into ultra low form. Do you know of any?

Jim, I did a quick "low sprocket/low pivot" model in some of Tony Foale's software. I took the default settings for a simple "damper near the axle" model rear suspension with 133mm of travel. The rear ride height is shown as 830mm and the CG height as 650mm. That shows that 1G acceleration without anti-squat being considered. That changed rear ride height to 764mm and CG height to 618.5mm. Factoring in the anti-squat on that default model had rear RH at 790 and CG at 630 so you can see it kept the bike from squatting so much.

I then dropped the pivot 100mm and the sprocket height 130mm to keep a somewhat similar relationship of the chain. For this version the RRH is 830 and the CG is 650mm (no change). With the 1G accel no anti-squat is 764mm and 619, with anti-squat 777 and 624.

Even though the rear now squats an additional 13mm the CG doesn't drop as much because the front is presumed to stay topped out under acceleration.

830-777= 53mm, and again, this is from a "full droop" reference position.

I have little doubt but that juggling the pivot/sprocket locations might be able to improve things for either model, though the caveat with the anti-squat is that "improved" doesn't always mean the same thing to all people/uses. GP bikes often have adjustable pivots and they use that because the squat geometry will vary with sprocket size changes. But I don't think they normally change more than +/1 1-2mm at most once they find a relatively sweet setting.

To get a similar chart on the wheel rate the low pivot damper needs to have the top mount moved about 50mm forward, which is some but not a huge amount.

You are thinking of Horst Leitner's ATK sprockets, and that does actually reduce the variance in squat geometry a significant amount on a long travel dirt bike. There's less variance to cause problems on short travel so the net change there from the ATK is not as great

A commuter bike with 8 BHP that never exceeds 45mph can probably work adequately with an amazingly wide range of settings. You could even go with a hard tail, eliminating chain geometry concerns, and use a cushy seat instead. :) My concern is for people who start hacking away when they have little to no idea that what they are proposing to do has any effect at all. A crash at 45mph can still put you in the hospital or morgue. The 8 BHP engine may not have enough torque to cause significant loss of ground clearance even with hugely pro-squat geometry, but it is always good to do some research first and try to get at least a mid-level "OK" design. If you've made things so the bike can't ground when leaned over at full bump, you could still have problems if the pro-squat bottoms out the suspension while leaned over and the suddenly infinite wheel rate causes a loss of traction.

beatr911, keep in mind that it was just a few laps on a different bike. The track is very short so a lap is about 1 minute. I looked through some old emails and found these comments where Arthur said "BTW, Emo thanked me for the spin on the bike, and said he could easily get 5 seconds a lap with minor changes. I believe him; he's a seriously quick rider. He wasn't specific about what these changes were. I will ask next time, especially if I can get another rider to test it." and "Given that proper racer Emo can do a 1 minute lap on my bike 5 seconds quicker than I can" and "I thought when other guys said they were impressed at my being "only" 5 seconds off Emo's time that they were just being polite. . . " but 5 seconds off the fast guy's time was respectable. So the fast guy hops on, reels off a respectable time, and says he could get another 5 seconds off.

Arthur's Kawasaki has a stock engine and doesn't run super-sticky tires as Arthur isn't interested in putting the money in it, he'd rather spend it on more track time. Other than the FF riding position the only real chassis change is the swing arm extension, so it probably is safe to say it will have performance much like a stock EX500.

The important thing IMO is that Arthur's bike shows that an FF riding position doesn't necessarily preclude riding in a respectably sporting fashion. And having a respected "fast guy" go out and come in saying he'd like to ride it some more adds some street cred to offset those who'd dismiss it out of hand.

One of the FFers was doing a Yamaha TMax with a Hossack FFE on it:

http://www.bikeweb.com/image/tid/101

And with that, I'm back to the garage to see if I can get things mocked up with wheels and the new cellulose composite chassis parts. :)

cheers,
Michael

Michael,

Thanks for the detailed response.

As you referenced that the ATAC was used on dirt bikes, I do recall seeing them on road bikes and reading about the merits of such an install. But as mentioned previously, as good as they may have worked, they did not last long in the market, and thus my comment that they may have fixed a problem that did not exist from a practical standpoint, still stands. :)

Well said.

From a practical standpoint, even a speed of 65 mph does not cause much squat in the rear because it typically takes about 8 hp to run at this steady state speed on a typical motorcycle. This also means that there is not much "load" on the rear swing, and thus the largest forces on the swing-arm arm from road imperfections, and/or cornering forces, as cornering would put more load on the suspension compared to 8 hp steady load (and resultant compression).

This still means at the acceleration I will be taking off at, the rear end squat is simply not much of a factor. In fact since one on a FF would be sitting lower in the frame, the overall CG is lower than a stock bike, and thus cause even less squat at the same acceleration.

I think if a person had no idea what they are doing in this regard, the project probably would not come to fruition in the end. At least I hope so.

Let's say a person botches the swing arm geometry, and it has a terrible amount of squat. The only time the motorcycle will be able to accelerate at full throttle, is with the bike upright. In other words, accelerating in a straight line.

Now let's say the squat allows the suspension to reach full compression. What will happen? Right, the under carriage will scrap hard enough to counter act the acceleration, and will quickly inform the rider that he/she has an issue to contend with. LOL!

Now if the same rider was foolish enough to try the same trick in a corner while being bent over at 45°, well then the rider would get a nice view of the road from the side of their helmet, as the under carriage would drag hard enough to make itself known very quickly.

I think this is what you are alluding to above.

Jim.

Back in the mid 1980's, there were 3 tire choices for sport bikes, the 16, 17, and 18 inch rim size.

My bike has a 16 front and 18 rear, and there was much discussion about this in the press.

My choice for the front would be maybe a 17 or 18 instead of the 16. The 16 is faster from a fast transition standpoint, but I prefer more feedback to steering in the front than the 16 provides. Just my preference. I've had numerous bikes with 18 sized wheels, and they felt "normal" to me.

Before 1985 or so, all the typical Japanese bikes came with 18's front and back, and then in the late 1980's switched to mostly 17's.

I really think it comes down to a personal choice.

Jim.

One bike I am considering has a 16"/15" the others are 18"/15" wheels. I too prefer good feedback especially in the front. The rear not so much, but stability and durability is important. The 17s just have so many choices on width, aspect ratio and compounds.

As for squat, you folks definitely have the experience edge to figure out how much squat/anti-squat geometry might be acceptable/required for say 20hp and 4" of travel.
I'll have to experiment with Tony Foales software to gain a better understanding of what might work well.

For the WR250R lowered seat aero project, my plan is to keep the steering/handle bars fairly standard. This will probably limit the amount of seat lowering I can do. I want to keep the fabrication requirements within reasonable limits on a first attempt. It usualy takes about 3 attempts before one has debuged the whole thing.
The stock fuel tank is only 7.5 L total [2 US gallons] this presents an interesting challenge, how fare can I go on 5.5L [1.5 gal]? can I get the fuel consumption down low enough to get over 400 km [250 miles] on 5.5L? This is 1.375L/100km [171 mpg US]? I do have a 15 L tank for this bike so if all else fails I can put it on and get the range I want.

When building a motorcycle project I think the first thing a person should do is ask "what are the best tires for this bike/application?" and once you've chosen those, they dictate what rim size/width you'll run. The tires are the one major item that you can't modify in the garage and that are a big factor in the ride qualities.

I had 16" wheels on my EX250, and tire choice was very limited and people would spend money to have their stock wheels converted to 17" (this was before Kawa switched to 17" on the EXs). 17" is where the tire companys have focused their efforts for the last couple of decades, but that focus is on 250cc+ bikes, not little bikes.

There's a fair choice in 18" because of the vintage bikes. The 250x18 Bridgestone BT39SS that came on the Dream 50 are very popular with the people racing CB160 Hondas, and they are very light and stick very well though they may be a bit too lightweight/soft for general street riding. Heidenau has several sport tires in small 18" sizes, and I think they also have some 17" for small bikes as they are used in "moped" race events in Europe. Heidenau also has some tires for different size scooters that are made with reasonably sticky rubber (as opposed to "rim protector" rubber) .

Heidenau Tires



Tony's software is very handy. The drawback is that it is up to the user to decide which set of numbers are the ones s/he want's to use; the software doesn't offer any "this is better" comments. It sure beats trying to do a bunch of manual computations but it can easily get to a "too much data, can't tell what is best" situation where I have to just pick one and go with it.

cheers,
Michael

Michael,

I agree with what you said above.

And to add to that. :)

Let's say we have a motorcycle that is setup with a good inclination of the swing arm while under power (anti-squat).

Now we are entering a curve, while still under power and we have adequate ground clearance to make the turn.

Suddenly a deer runs across the road in front of us, and yikes, we have to back off completely (let's not even talk about grabbing the front brake hard).

What happens?

The power is lost so the suspension drops and now the undercarriage hits the ground, making it very hard, if not impossible to make through the turn.

This is exactly what happens to a bike with shaft drive and a big, powerful motor too. It has natural anti-squat tendencies.

I would prefer to design the rear swing-arm so that it squats under hard acceleration and therefore does not "drop" when you remove the power source while in a bend in the road.

Normally when a seasoned rider is in a turn, there is a slight amount of throttle held on to keep the same momentum through the turn, and not scrub it off with the front tire. This action keeps the chassis stable and also keeps adequate ground clearance throughout the turn. One typically would only add an excessive amount of power in a turn in this scenario, 1) if they are wreckless, or 2) want the undercarriage to hit, or 3) want to see how close they can come to crashing.

I tend to use the "Kenny Roberts" technique of rounding a curve, which if anything implies that I ere on the side of too much throttle through a turn as this would kick out the rear slightly and still allow the front to steer the motorcycle. This action is a polar opposite of how Kel Carruthers (spelling) of the Yamaha racing team used to ride through turns. His front tire was gone after a race, while the rear looked pristine. The main drawback to this of course, is that if he pushes too hard and looses the front, the odds are that it's gone for good, and he's down!

Obviously this also implies that one is not going too fast through the turn to begin with!!

Sorry I did not think of this sooner as it came to me in bed last night.

Jim.

Jim, another consideration, which Tony mentions in his book, is that having the wheel (either one) move up and back when hitting a bump makes for a better ride. With a dropped s/arm pivot you'll see the rear wheel moving up and forward.

FFers have mentioned that it is important to have a some "spring" in the seat back so that bumps don't jar the rider so bad. You can't "post" on the pegs over bumps as with a conventional riding position. Gurney may have gone to the extra bother on the Yamagator chain run to improve the way bumps are transmitted into the bike.

Owners of shaft-drive bikes (especially BMWs) do learn to not chop the throttle in mid-corner. I've never ridden one of the more modern shaft setups that float (like a BMW paralever) but they should have less jacking in the rear suspension from drive forces.

No doubt the importance of squat effects depends on how fast/hard/powerful the rider and bike are. For high gas mileage and gentle riding they are probably not a huge concern.

Oh good, someone else who suffers from "project insomnia". :) I have a bad habit of waking up about 2-3AM and then getting started thinking (for the next 2-3 hours) about whatever project I'm working on.

cheers,
Michael

Michael,

Is Tony Foale's first book worthy of a purchase?

After your nice discussion through this post, you have my curiosity up.

Jim.

Jim, do you mean the one with Vic Willoughby as co-author? If you find a used copy at a low price I don't think you'd go wrong getting it. But Tony's latest edition "Motorcycle Handling and Chassis Design" incorporates everything in that first book and adds a great deal more so if you are only going to have one or the other, go with the current book.

John Bradley's books are a two volume set, with the first book being the "design" book and the second book being the "build it" material.

When I was John's US distributor I also sold Tony's book and software, and I encouraged people to get all three books and never had anyone say they'd regretted it.

Tony and John's books have some common material (not surprising) but they had different goals in writing them. Tony goes into much more detail on theoretical aspects, while John wanted books that would inspire people to take it out to the garage, do some measurements and calculations (as illustrated in the Volume 1), and then move on to changing/building things. Of course, Tony discusses construction topics too, but John goes into much greater detail in Volume 2 on material selection, construction techniques, etc.

So by getting all three you get a broader spread of knowledge than with just John or just Tony's book(s).

cheers,
Michael

Doing a few mental exercises of trying to figure out where to put all the components on a FF design (radiator, engine, battery, oil tank, fuel tank, airbox, etc), it seems like it would be very hard.

Then I thought about how this might be much easier with an EV setup, especially if you are making your own frame.

Take one of the Zero motorcycles for the components (electronics, battery, motor), and then you can mount the motor and chain drive with a shorter chain behind the passenger, while you can put the battery down low between the rider's legs and the electronics on top. I would probably go with a longer wheel base and a remote steering head, but there may be ways around that.

Just a thought.

Oh, and don't forget Velomobiel FF aero scooter. He put the foot pegs on bars running down parallel to the forks (wider) and thus kept out of the way of the front wheel turning.

You also need to consider the effects of different locations for the parts on the center of gravity of the vehicle. E-bikes may eliminate some parts (you'd think no radiator, water pump, hoses etc but then some more powerful electric motors use those parts) but a sufficient quantity of batteries may be both very heavy as well as bulky. You might be able to locate individual cells/batteries in different spots instead of all in one location, but you have to then consider if that makes it more difficult to service or swap out discharged/damaged cells.

A spread sheet is useful for determing the overall CofG by having a line for each component along with its weight and where the component CofG falls in the assembled vehicle. You sum all of that together to arrive at the combined CofG. Don't forget to include the CofG for the rider/passenger too.

You need a reasonably accurate scale, and everything needs to be weighed. You'll probably need several scales in different ranges. A freight scale suitable for weighing a 160 pound motor is probably going to lack resolution for getting accurate numbers on light parts. If the CoG of the part isn't obvious (say a rectangular battery vs an exhaust system) you'll need to determine the location of it. That can be done by hanging it from different points and drawing a line across the part directly below the hanging point. Where the lines intersect is the CofG. Here's an example where I hung a motor from different motor mount bolts with a plumb line from the attachment point on the hoist:

http://www.eurospares.com/graphics/y...f/yz250cog.jpg

That will help on the footpeg bracketry, but you still need to ensure the rider's legs clear the tire. I'd have some concerns about the parallel footpeg mounts being more prone to flexing because of a longer unsupported run of tubing. You can work around that by increasing the tube diameter but that might end up bulkier or heavier than a triangulated structure. With a lot of this stuff you will probably start off with several different possible ways to build the component and then you have to mull it over and figure out which works best, keeping in mind that "best" for that component may mean "not so good" for the way it interacts with some other part. Try to not design a part in isolation, but rather keep in mind how everything may best work together.

It can drive you mad trying to keep track of everything. :)

cheers,
Michael

Michael,

I ordered John Bradley's first book this weekend.

Around $40 used if I recall correctly.

Thanks for the tip!

Jim.

If you see a copy of Volume 2 you should buy it. I had an email from John over the weekend and he said that he's out of V2 and it will be a while before more are printed. Powell's in Portland OR has carried both John and Tony's books and might have some on hand so you don't have to order from England (John) or Spain (Tony).

I think you'll like the chapter in Volume 1 on aerodynamics. There's a full page listing the results of about 30 wind tunnel runs on different changes to an LSR bike and I found that very interesting.

Here's John's website:

Broadland Leisure - Publishers of The Racing Motorcycle

and Tony's:

TONY FOALE DESIGNS - Home page

cheers,
Michael

Michael, thanks for those references! Lots learned just from the sample pages. I'll be ordering soon.

http://www.eurospares.com/graphics/c...CS for R6 hub/

I've added a some photos showing recent progress on the hub center FFE (funny front end) for my "gator-ish" project. I've made the bearing carriers and the new carrier for the 315mm Brake Tech/Axis cast iron rotor.

I didn't find a photo of how the lightening holes in the Axis R6 carrier were done until after I'd played things safe on the one I made. I'm not going to spend the time now to try and shave a few more ounces off since this will be a street application.

I was forced to do some tidying up in my office room and the garage as I couldn't find the small bag with the rotor buttons. It eventually turned up in a middle layer in a tub sitting next to the mill. I suspect it had been sitting on the welding table when I needed to clear it and all the miscellanous stuff got pushed off the table and into the tub. I must admit that the extra floor space in the office and the stack of empty boxes and tubs in the garage are proving to be mood improvers. :-)

cheers,
Michael

FF info
 

Royce Creasy very kindly supplied me with a pristine Voyager brochure and
a copy of his FF Info Pack and said it was fine to scan them and his "What Ever Happened" (I used my somewhat wrinkled copy) and make them available.

I've put them in this folder on my website:

Index of /graphics/FF

There's an 8MB

FFInfoPack.pdf

three pages of the brochure (I stitched pages 2 and 3 together)
that are 4.4, 13 and 5.1MB :

VoyagerBrochure001.jpg
VoyagerBrochure002plus003.jpg
VoyagerBrochure003.jpg


The color brochure scans are fairly large format/high res and should
look nice if printed off.

And Royces retrospective at approximately 14MB:

WhatEverHappened.pdf

cheers,
Michael