Key learnings and time well spent

It’s been a while since I made any updates here on the site, but I’ve been busy out in the real world laying the foundation it will take for this project to be possible. More specifically, I’ve spent basically the entire previous year working on several different motorcycles. If I had to put a number on it, I’d say that my mechanical knowledge and experience has at least tripled since I first thought of this project. I’ve rebuilt carburetors. I’ve rebuilt brakes. I’ve rebuilt suspensions. I’m in the progress of rebuilding two separate engines into one that will hopefully run.

While none of this work has been directly related to Project Streetliner, it’s all been tremendously helpful in laying a solid foundation of both component knowledge and general motorcycle understanding. As much as the Streetliner looks like a car in the latest renderings, it’s still basically about 90% motorcycle. It’s a three-wheeled cabin motorcycle where the frame is doing double duty as a safety cage. Having now pulled several bikes apart in pretty significant ways, I’m feeling so much more prepared to take this project on for real. I know I won’t do this alone, but thinking back to a year ago, I’m now so much closer to being ready to kick this project off. Funding is still a huge question mark, but money aside, I’m feeling a lot closer to getting this project started from a place where success is that much more likely.

On the funding front, I’m thinking very seriously about putting this up as a Kickstarter project. I’m thinking I’d need to raise about $15,000, which is pretty small by their standards. What I’d love to get everybody’s input on would be this: what incentives sound appealing to you guys? I was thinking perhaps of a range from high-quality prints of the renderings (like a poster series), all the way up to a complete set of kit plans. What do you guys think? What would you pitch in $50 for? How about $500?

The case for ATV drivetrain

Oft contributor and friend of Project Streetliner, Aaron, has more than once made the case for using the drivetrain off an ATV (or “4-wheeler” as we southern kids grew up calling them). At first blush, I’ve always hated the idea because I’m a scooter snob. I don’t know ATVs and I don’t care about ATVs. But there’s one big factor that makes Aaron’s case for the ATV drivetrain impossible to ignore: reverse. From his previous comment:

IMHO… I’d say to go with a small ATV engine for several reasons.

1) They are virtually identical to many motorcycle engines, except their gearbox has reverse, which will save you a lot of hassle later.

2) Many of the “manual shift” variety have an automatic clutch, which will gain you most of a scooter’s “twist-and-go” convenience while still keeping the ability to gear up simply by changing sprockets (something you can’t do easily with a scooter – see Craig Vetter’s woes with his Freedom Machine). Even if you decide to go with a CVT ATV instead of manual, you can still run a sprocket/chain off the bevel drive that normally drives the rear axle.

3) ATV engines are commonly larger bore single cylinders which are setup to generate a lot of low end torque, which will be useful after being geared up to your desired top speed. Many small displacement motorcycles don’t have a lot of torque and may have to be geared down to move a heavier vehicle then they were designed for as quickly as you’d like (especially if you decide to make it a 2 passenger trike).

4) Depending on what you decide to do about the front suspension, you may get many of the parts you need right off the engine donor.

5) If your EV desires grow, you can always retrofit it with one of the Motorcycle EV Conversion kits coming out lately. That option won’t be as easy if you start with a scooter engine/swing-arm/wheel.

6) And last, I don’t think the hp difference will be enough to limit you to surface street speeds with a gearbox to choose your final drive ratio. With a CVT or EV you have the problem of being “wound out” at your peak RPM and not able to accelerate further. Craig Vetter had this problem as well. With a gearbox almost any engine that will move you 55 with “power to spare” (as you dictated) will also get you to 70 for highway runs.

I really can’t argue with any of this. Especially with many of the “sport” ATVs on the market today, horsepower won’t be in issue. I wonder a little about just how these engines are tuned, given that mpg isn’t your primary concern off road. They might be set a lot richer to allow for higher performance. If their carbureted, that’s not so hard to fix, but if they’re EFI, which most are these days, then getting that re-mapped could be quite tricky. I really only have two concerns: weight, and form factor.

Weight is an obvious concern, as the less weight the Streetliner has to haul off the line, the more efficient it will be. Some of this can be overcome with gearing and aerodynamics, but the lighter the better is a good rule of thumb. I’m concerned about weight in the ATV primarily because it’s a 4WD vehicle. I only need to drive one wheel, so I’d effectively have a second output shaft and differential just getting lugged around with no purpose. The most mad scientist thing I can think to do with that second shaft would be to run an air conditioner compressor off of it or perhaps a second alternator. That has interesting connotations, but I’m still not sure.

The more troubling concern is that of form factor. What I’ve designed so far has a wheelbase about 4″ longer than my MINI. Granted, the MINI is not a big car by any measure, but getting much longer than that worries me in terms of low-speed maneuverability. I don’t want the thing to be so long it can’t easily park. The guys who build those impossibly long chopper motorcycles run into this all the time. Their stretched-out bike can barely turn around coming out of a parking lot without doing a 12-point turn. I know that’s hyperbole, but I still don’t want to go down that road if I can help it. The scooter drivetrain has not just an economy of engineering simplicity and bolt-on convenience, it has an economy of space. Without knowing more about the ATV powerplant, I’m not sure if I can cram it in behind the seat on the Streetliner the way I’d want to. I doubt it’s impossible, I just need more information.

So it’s certainly on the table. I need to get some measurements and figure out which ATVs would be good candidates. Looking around online, the tricky thing is finding one that isn’t shaft drive. For this to work, I really want to have the final drive be chain and sprocket so that I can adjust the end gearing as easily as possible. I guess we’ll see.

Any thoughts?

Existential crisis of criteria?

Things have been quiet here at Project Streetliner for a while. Progress is paused on my small-scale prototype while I wrench on a pair of old motorcycles. Meanwhile I’ve had a lot of ideas rolling around in my head. Thing is though, these haven’t been ideas of progress, but rather ideas on how this project might drastically change.

Right now, the vehicle is designed as a tilting, petrol-powered, highway capable commuter vehicle. Thing is though, my commute now is mostly city streets. Do I really need to do 70 mph? If I’m just zipping around surface streets, is the leaning really needed? Is there actually an opportunity to do a full EV or an EV + generator hybrid vehicle? That has me wondering if I shouldn’t re-spec this project for something closer to my actual use scenarios. Should I shift to more of a velomobile-style bike path runner?

For example, one idea I keep thinking about is basically taking apart a golf cart f0r its motor and controller, welding up a custom solo frame, then maybe adding Honda’s smallest generator for onboard charging. If it’d just be a bike path / lane vehicle, then there’s no real need for a full cage. I’d still be wrapping the whole thing in some sort of aerodynamic body. That’d be pretty sweet.

The other idea I keep tossing around is a non-tilting version of the Streetliner — something perhaps a tad lower and a bit wider up front. This concept would still be scooter or motorcycle based and highway capable, but having a flat trike setup means a slightly simpler chassis and suspension setup. I’m really ambivalent about this one, simply because it isn’t that much of a complexity save. It would mean a control change that could be nice — that is, I could use conventional car controls rather than a handlebar and motorcycle controls.

Speaking of motorcycle drivetrain, that’s been on my mind as well. I understand those mechanicals a LOT better than I used to. An older, air-cooled japanese motorcycle engine is simple, reliable, powerful, and even reasonably efficient. Parts are still abundant, and whole, running motorcycles are available for less than $1000. Changing sprocket sizes for different gear ratios is really easy if I go the motorcycle route. That coupled with the aerodynamic gains from the body shape should make my 60 mpg goals pretty easy to reach. The disadvantage there could be weight. But if my efficiency goals can be met, then does an extra 100 lbs really matter?

The last conceptual quandary I’m trying to figure out is broader purpose. That has a couple of connotations. Do I optimize the vehicle as an in-town commuter with highway capability for getting around town on the bypasses? Do I optimize for surface streets only — so a top speed of 55 mph or less? Or do I optimize the Streetliner as a long-distance touring vehicle? A coast-to-coast road trip at 60+ mpg would be pretty cheap to do. But it’s not just me these days. For a long-distance tourer, I’d want to be able to have my wife with me and we’d need at least a little luggage space, even if we’re traveling light. That’s a pretty big change to design criteria. I’m open to it, but like any of these questions, it’s a significant shift from the current concept. Decisions, decisions.

Any thoughts?

Donor bike options

Last weekend I laid fresh eyes on Kymco’s Xciting 500Ri and think that it could be a very viable contender as a Streetliner donor bike. Up to now, I’ve been leaning toward the Suzuki Burgman 400. The Burgy’s mileage is good, the motor is powerful, it’s a twin disk brake up front (meaning one disk/caliper set per wheel) and it’s a popular bike so the second-hand market should be pretty good. However, the Kymco has more than a few things going for it. The weight is the same, the mileage is similar, two front brakes, 12V accessory plug-in, good looking gauges, it’s got an extra 100cc of engine, but most interestingly an adjustable twin-shock rear suspension. The Xciting is also a bit less expensive, but still with Kymco’s proven Taiwanese build quality. In fact, I can’t help but feel a tad more confident in the Kymco, as they have so much more experience with scooters than Suzuki does.

But back to the suspension, which is what I’m most interested in. The rear suspension on the latest generation of the Burgy is a mono-shock underneath the frame. The Kymco uses the more traditional twin rear shock setup like I have on my Vespa GT. Previous Burgy models used a similar setup. What I’m wondering now is which will be better in my intended application? It’s easy to assume that the more sport bike style mono shock underneath the newest Burgman models is in fact an upgrade. But it could just as easily be a cost-saving measure. I’d probably have to ride both bikes to see if there was a difference in feel. But beyond the performance in the stock bike, how would that rear suspension behave plugged into a likely heavier vehicle with completely different geometry? A beefier shock will likely be needed. Will I be able to easily source one for the Burgman? The more traditional twin shock setup on the older Burgman models and the Xciting seem to offer greater flexibility. There’s already a nitrogen shock upgrade available from Kymco. But more than that, with the mount points so straightforward, I could conceivably use almost any shocks I want. In order to tune the suspension on the Streetliner, I’m going to need both dampening and pre-load adjustment. Although the current Burgman shock has seven levels of pre-load adjustment, it may not be the correct dampening. Fitting a different shock may involve some serious modifications. One of the guiding tenants of this project is to do as little engineering as possible, so the idea of having to re-engineer that more complex subframe to accept a different shock is not appealing. The sacrifice is that if I’ve got quite a bit of room above the engine for storage in the body of the vehicle. If I’ve got to have shock mount points above the motor, that could encroach on some of that space. But in the end, it’s not about maximizing cargo space, it’s about maximizing efficiency, comfort, safety, riding fun, and style.

Surprising weight

I’ve refined my safety cage a bit and done some more research into safety cages used in racing. I found a kit that featured 1.75″ tubing with .135″ thick walls. Running that through the online weight calculator I’d found, that comes out to 2.133 lb/ft. I also did a calculation on 3/4″ tubing of the same wall thickness for use in cross ties and such. Figuring out the length of the tubing in this design, I was able to do some weight calculations:

This is all obviously napkin math, but the result is pretty surprising. If I use the 1-3/4″ tubing for the main structural hoops, then tie it all together with 3/4″ tubing, my entire safety cage and main chassis would only weigh about 100 lbs 130 lbs. This doesn’t include some sub-frame pieces and none of the front suspension components, but still, that puts me well on my way, I think, toward making my < 600 lb design criteria.

Wheel size, wheel pants, stability and leverage

They were apparently absolute murder to ride, but nothing quite says vintage transportation like the Velocipede. The thing I’ve always found fascinating about these is their huge front wheels. The physics of a bike like this must feel very odd compared to bicycles of today. The force of angular momentum of a wheel (the force that makes it want to stay upright and that leans it when you top turn it) is directly proportional to the torque moment of that wheel. Or, said in non physics babble, the bigger and/or heavier a wheel is, the more stable it is when its rolling. It’s kind of an amazing force, when you think about it. The two tiny rollerblade-like wheels of a little razor scooter generate enough angular momentum to hold an adult upright. In larger, powered two-wheelers like scooters and motorcycles, wheel size makes a huge difference in the character of the machine. Scooters have traditionally had much smaller wheels. Most vintage small-frame Vespas had only 8″ rims, while their large frame brothers weren’t much larger at 10″. My modern Vespa has 12″ wheels, but still feels very much like a scooter — agile, and a tad butt-heavy. Motorcycles tend to have anywhere from 14″ to 22″ rims depending on the style. When I test rode a Triumph Bonneville in 2008, what I noticed immediately was that it took about half the speed I was used to in order to get rolling stability. Once moving, the larger wheels and rolling mass of the Bonneville felt so solid — like it was on rails. What would wheel size mean for the Streetliner?

Bigger front wheels
While playing with the proportions and broad strokes design details of the Streetliner this week, I wondered what would happen if I swapped out Burgman-size front wheels for larger wheels from another bike in the Suzuki fleet. The size of the rear wheel is likely fixed because of the shape of the engine/transmission casings. Big wheels up front would definitely give it a stronger visual connection to the old race car designs that have inspired the project. Especially if I grabbed the spoked wheels off of something like the Boulevard S40. But beyond aesthetics, it would make some significant differences to handling comfort, lean feel, and possibly even make the front suspension easier to build. It looks the business though, doesn’t it?

That’s an 18″ rim up front as opposed to the 14″ stock Bergman rim on the rear. It definitely calls back some nostalgic racing mojo. Larger diameter wheels would mean that the front end would take bumps better and have greater rolling stability. It’ll also mean more room inside that wheel for all the tilting mechanicals, brakes, and steering attachments. What it would also mean is that the lower and upper swing arms of the tilting suspension could be further apart — letting me have not only better ground clearance, but deeper leaning on the same distance between the wheels.

If you go back to my initial lean study, I explored the relationship between body height and leaning. With the larger wheel size up front, a couple of good things happen. First, I’m able to spread the swing arms apart, meaning that at the same lean angle, there’s less interference. This is important at both the wheel attachment points and where the dampening assembly will go (the shocks and their connecting structure, which isn’t shown). The more room there is to work in those assemblies, the better. Not only will it be easier to build, but it’ll mean more opportunity for building fine tuning and adjustment points right into the structure.

The biggest difference may indeed be felt in leaning stability. The greater mass of those larger wheels would mean nearly instant leaning stability. Whenever I see a Honda Goldwing slowly lean its way through an intersection turn, it amazes me that the 900 lbs or so of the Goldwing are able to be held up at such low speeds. The Goldwing has an 18″ wheel up front and a 16″ wheel in the rear, and that’s enough to keep it stable, even at low speeds. With two 18″ wheels up front, the leaning stability ought to be massive. But more than that, having the swing arms further apart vertically, means that the side-to-side forces generated by the wheels when they precess (based on steering input) will not only be greater, but have more leverage on the body of the vehicle.

The one thing I wonder about, however, is what it will do to the driving feel of the vehicle? Greater stability means that it will take more input force on the steering to induce the lean — and that force will grow with speed. That’s a good thing, as you wouldn’t want the vehicle to be all twitchy at 70 mph. I’m not worried about it, I just wonder what the feel will be. I imagine it wouldn’t be much different than a big cruiser motorcycle with the Tilting Motor Works kit installed.

Wheel pants
From the beginning, I’ve envisioned the Streetliner with wheel pants for added aerodynamics and efficiency. This inspired by both ’30s era aircraft like the Gee Bee but also similar projects like the Aptera. Exposed wheels simply aren’t very aerodynamic. Putting a streamlined shroud around the wheels will add effeciency (and look fantastic). However, I’m not exactly sure just how much efficiency is gained. Adding wheel pants will definitely add time and complexity to the build, and at some point I’m going to have to do an aerodynamics study to see how much more efficient the shrouded wheel is than a naked wheel. One thing I have to keep in mind though, is that unless I can put a decent tail on the pants, there won’t be much advantage in the wind. However, that tail will quickly limit how far I can turn the wheels (because the tail of the pants will hit the body). That means a large turning radius, and for a vehicle intended for mostly city use, that’s not a good thing. So if I have to sacrifice wheel pants for the sake of turning ability, that’s a compromise I can’t not make. But I do just love the look of the pants. I hope I get to keep them.


Surprised by size

Tonight I’ve done some further playing in Illustrator to try to flush out the reality of the Streetliner’s real world dimensions as I’ve envisioned it. What I found is surprising, namely in just how much bigger the vehicle is than I imagined. Like many of yesterday’s discoveries, it’s a pretty big “duh” once I step back and think about it. If I move the motor back and place the driver in a long, recumbent position, then I’m going to end up with a vehicle quite a bit longer than its Bergman donor. Observe:

The driver representation is calibrated to my height, and I’ve even been able to reproduce the Bergman powerplant close enough for this kind of ballpark purpose — including some of the Bergman sub-frame for the engine mount. I was pretty surprised to find that by bringing the driver down and leaning the seating position back into an ergonomically correct position it added about 40″ to the overall length. That got me thinking, how would this vehicle compare size wise to say, my MINI Cooper S? Turns out, the Streetliner in this configuration would be roughly the same length as my MINI hatch. I discovered yesterday that in picking up the body relative to the wheels, it put my eye height at roughly the same height of my MINI as well.

The MINI makes a very convenient measuring stick for me because it’s not only a small car by normal, American standards, but I drive one almost every day. In a lot of ways I feel like the MINI is about as small as a car can be before it starts getting hard to see by other drivers. I’m used to driving hyper-defensively from riding my Vespa, but it’d be nice to be that much more visible all the same. It was a surprise though, to see that the Streetliner in this configuration would indeed be a bit longer than my MINI and only a few inches narrower in track.

It’s important to remember that the width of the actual vehicle body will be about half that of my MINI and much more aerodynamically shaped. This should present perhaps as little as a third of the frontal area to the resisting wind. Combine that with this vehicle weighing less than 25% what my MINI does, and likely using an engine with about 25% the displacement and funny enough, 25% the horsepower. That should make for impressive mpg gains without even touching the engine gearing. All while likely retaining a top speed of around 100 mph.

It’s exciting stuff. I also started mocking up the basic configuration of the safety cage/chassis, but that’s another post all together.


Body height to lean angle study

With the broadest strokes of the exterior design penned as far as is practical at this point, it’s time to do some real work. Up to now, I’ve pretty much just eye-balled it. With the pieces starting to come together, it’s time to get more specific and more precise. So today I explored the relationship between body ground clearance and tilt geometry. There are a lot of factors effected by this relationship. Some I anticipated, some I didn’t.

The major factors are these:

  • Lean angle
  • Ground clearance
  • Center-of-gravity shift
  • Eye height of the driver

Tilting Study A

I started with a low profile body height that would keep the suspension swing arms essentially level. From studying the Brudeli Leanster, it looks like so long as the swing arms are parallel, they need not actually be level. This makes sense as I start to lean the elements visually. One of the things I was most curious about was the relationship between body height and maximum practical lean angle. Tilting things over in Illustrator, it looked like 35º was about all I was going to get before bodywork was likely to start scraping. My first surprise was how far the rear wheel slid right, which made instant sense, but was unexpected. It’s exciting to see just how far over that body swings from centerline — pushing the center of gravity deep into the apex of the turn. Given that it’s nearly impossible to low-side a tilting trike, moving that much mass to the center of the turn has me pretty jazzed thinking about the cornering capabilities of a vehicle like this. My one hesitation is in line-of-sight. Sitting too low is a major safety concern.

Tilting Study B

So what happens if the body gets picked up quite a bit higher than the wheels? Using the same length swing arms, this obviously brought the front wheels in tighter to the body. The end track of the vehicle is yet to be determined, and it’s not as though the swing arms can’t be lengthened if needed. I was again surprised at just how far the rear wheel swings from side to side. A deeper lean angle of 45º seems likely in this arrangement. 45º is considered the standard of a deep lean, as this is the depth to which sport bikes are able to lean — their riders laying padded knees into the asphalt. In essence, this is what having two wheels up front does for the Streetliner. There is an issue with this kind of arrangement, however. A closer examination of the swing arm attachment makes it look pretty obvious that unless I bend the ends of the swing arms, they’re going to interfere with the outside wheel. Also, if the body is too high, then I’ll need a really wide track to meet one of my minor design criteria — that leaned fully over, the vehicle will not actually tip over and fall if not moving. With no ability to put my feet down, this little detail is crucial. On the positive, it’d mean a nice high line-of-sight. It would seem prudent to find something in between.

Tilting Study C

In splitting the difference, I found a nifty elegance. By aligning the bottom of the body with essentially the axle height, I think I’ve found the sweet spot. 40º seemed easy with only the wheel pant in danger of interference. I bet 45º would be possible depending on the engine and transmission casings.  With further study and measuring, this configuration yields an eye height of approximately 47″. This puts it almost exactly where my line-of-sight is in my MINI, which is actually very good. But more exciting is as much as 9″ of ground clearance. That should make for both very clean aerodynamics and easy road going over fairly substantial road hazards.


Obviously, this is all just estimation, but it’s been a fascinating thought experiment. It’s also yielded a deeper understanding of seating ergonomics, but that’s for another post.