Entry and exit: its ramifications on exterior design

There’s been a lot of activity on the Streetliner drawing board this week. If you’ve been following along, you’re familiar with the shape above. This ’30s era race car inspired shape is what I’ve been showing people when they ask about what I’ve got in mind for this project. I love it, but I knew all along that this shape would inevitably change and evolve.

Likewise, one major aspect of the Streetliner’s design had yet to be worked out in concept: entry/exit. How the hell do I get in and out of the thing? It’s not that entry and exit is terribly complex, but in figuring out a good way to get in and out, it meant big adjustments to the exterior design of the car. So like any design undertaking, this needed criteria.

  • The integrity of the safety cage needs to be maintained as much as possible
  • Getting in and out has to be simple. No folding myself up snaking through impossible openings
  • I must be able to exit the vehicle even if the primary door system fails


So starting with the current exterior design, a handful of things have been adjusted since I first penned Design Concept Alpha. The overall length increased, the front wheels got larger, the wheel pants got longer and no longer turn with the front wheels. I really like this shape overall. The snout shape of the front end is very pleasing, the rear has a lovely duck tail quality, and I especially like this design because the vehicle looks even better with its canopy on. All of that shape, however, is mated to an underlying safety cage and chassis:

With arches as the vertical pieces, the safety cage design is pretty straightforward. Heavy duty curved bulkheads are connected by heavy duty rails, then everything is cross-braced in a truss of smaller diameter steel. The angled front and rear main plates actually create rudimentary “crumple zones” where impact damage would send the motor assembly and or front suspension components under the vehicle in the event of an impact. This design is structurally sound, but it has one major flaw: how the hell do you get in and out of the thing? The height of the cockpit opening lip is right at 36″ in this design. I’m pretty tall, but that’s still quite a height to throw a leg over while getting in and out. I also realized that I’d only given myself a 24″ deep opening front to back. I’m not a whole lot narrower than that myself (it’s winter weight, I swear!). So the practical concerns of getting in and out of a high, narrow opening are pretty significant. But even beyond entry acrobatics, with such a narrow opening, I wouldn’t be able to see my hands or any cockpit gauges. That top opening needs to grow and dammit, I need a door. The tricky bit is how do I add a door without compromising the safety cage?

One thing at a time. I added an approximation of the front suspension “box” and see where and how that should tie into the frame. I lowered the bottom rails to tie in to the front and also simplify the rear subframe where the mono-shock would attach. I also moved the main roll hoop back just slightly where previously it was implied that it would overlap my shoulders. Upon further reflection, I realized that this being a single seater, I only need one door. Even though my diagrams here show the opening on the left side, I think I’m going to opt for the right side having the door. Since the majority of motorcycle accidents involve people violating your right of way from the left, it makes sense to me to leave the left side solid. That written, the underpinnings of the door as I’ve envisioned it are as substantial as the major parts of the cage. That way when it’s closed and latched, the door becomes part of the safety cage. I like to think of it like the harness that comes down and locks in when you get on a roller coaster. Solid. Also, thinking about an impact scenario, that’s a force into the cage, so if the door is structurally captive against being pushed through the opening, it ought to be as good as solid. With the door opening on one side of the vehicle, the canopy (when attached) could hinge along the opposite edge — making for a very easy time getting in and out.

With that adjustment made to the frame, the body shape needed adjustment, as you can see below. The opening needs to be increased to meet my design criteria for being able to exit the vehicle in a pinch through the top without using the door. The bottom profile of the body shape also needed to be adjusted to account for the front suspension box.

Now with the shape updated, I like it even more. The larger top opening not only gives the whole vehicle a better proportion. It looks smaller and more trim overall. Before now, with the length being about that of my MINI (which I know, isn’t exactly big), the Streetliner has looked strangely large. Now it looks much more like the race car cabin scooter it was always meant to be. I also reshaped and shortened the wheel pant to account for the door opening.

I really felt like the new shape came into its own with the canopy in place. Not only was it less bubble-shaped, but it completes the curve created by the tail. I can also imagine much better visibility and comfort within the cockpit. That led me to consider some alternate front end shapes. One of which was the sloped, Ferrari GT-style nose. It would borrow its hood scoop aesthetics from a different era than I’d previously been thinking, but I really like it. Forward visibility would be better and overall aerodynamics might be a tad stronger with this sloping approach.

All that remained at this point was to add some visual interest to these basic shapes. This included sculpting the rear and adding a sort of LeMons-style front lip to the wheel pants. I really don’t want to overlook subtle details throughout the shape. Sure, a perfectly smooth Velomobile kind of shape is terrifically aerodynamic, but without at least some minimal sculpting, I think the shape would look like it were stuck in the ’70s and just generally unfinished. These details will surely evolve as the project progresses, but I’m loving it so far.

As I look back on the progression, it’s amazing how much influence a little thing like a door can have, but all for the better! This shape still has a lot of classic Italian sensibility, a lot of race car mojo, and plenty of salt flats shape credibility. As much as I love the ’30s sensibility of Concept Alpha, I like this even better. But more than that, I’m glad to have another big piece of the conceptual design puzzle in place.



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.


Evolution of design

There are innumerable details that will need to be worked out and documented before I cut the first piece of steel or even purchase a donor bike for this project, but I am very excited to see a lot of the big picture stuff starting to come together. Yesterday I was introduced to the Cycle Kart website and on that site is a PDF that lets you play around with your own race car designs. I took that a step further and what I’ve come up with may very well be the alpha design for Project Streetliner.

Starting with the original artwork, I kept the european style race grill. I am completely in love with this era of race cars. There’s a more contemporary tie-in though — a whole class of open-wheel streamliners that race for land speed records at Bonneville.


First step was to make a trike out of it. Go go gadget Photoshop!


With the correct number of wheels in play, it was time to scale them down to the correct proportion, about a 14″ wheel. It was at this point that I also realized that the “engine compartment” of a car like this would make a splendid luggage compartment for the Streetliner. I also faked a bit of the tilting suspension and removed some of the superfluous body shape details.


With the wheels properly sized and placed, I added rough wheel pants. I love the open-wheel look, but with efficiency the name of the game, wheel pants are a must. It’s amazing how much they alter the character of the vehicle. What before still looked like a toy ’30s era racer, now looks like a ’30s era airplane. Whatever the final shape, if the vehicle is strongly identifying with a particular era, I want to carry that through in the design details. I’ve also thought about perhaps a steam punk influence — lots of wood and brass.

I also lengthened the rear end to accommodate the rear engine placement, and raised the rear up to serve as more comprehensive roll protection.

I corrected the perspective on the luggage door, and moved the louvers down to act as somewhere for air to exit after it passes through the radiator up front. I also deleted the steering wheel and added a small windscreen. Like with a motorcycle of scooter, it needs to stay low enough that its lip is just below my line of sight. My plan is to have a soft top tonneau cover for those days I get caught in the rain unexpectedly, but also a removable hard-top canopy for those days when I know it’ll be raining.


One thing still troubled me. As I looked at fitting a canopy, the head-and-shoulders profile of the rear end had to transition to the smooth arc of the windscreen. Not only would that make for quite a troublesome fabrication, but the visual distortion would be like driving in a fun house. No thanks. It’s a little less aerodynamic, but this shape is going to be infinitely simpler to construct both the underlying safety cage and the canopy. I could always vent the areas left or right of my head for less drag when open.


Finally, a mockup of the canopy.


The more time I spend with this design, the more I really like it. Obviously, it’ll evolve, but this style has a lot going for it. It’s incredibly low profile, should be relatively straightforward to construct, and with the ample luggage compartment it ought to be very practical. It’ll also look like absolutely nothing else on the road, and I love that. But it ought to also be very comfortable, impressively safe, and downright useful.