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.