My Elio Alternate Project Is Underway.

[Mark BEX]

I spent a surprising amount of hours today in CAD getting a bracket/mounting setup for the rear swingarm that I was happy with. Took the file to the laser shop, and their computer was down, so hopefully tomorrow they will be cut.

Note the front of the swingarm is very wide, this is to stop it coming forward into the passenger compartment in the event of a vehicle hitting it up the rear. I will try to design it so the wheel goes under and lifts the BEX up the taking impact energy away.

The rear suspension strut should be something like this:

Great news for me for future stuff, the laser shop has taken delivery of a laser tube cutter, the first one in our city. Here is one in action for those who don't know what they do ..

 

[84mpg]

That laser tube cutter is a sweet piece of equipment. Pretty amazing...
My Dad wouldn't believe his eyes if he saw it. (He was around metal his entire career...)

 

[JEBar]

if the rear tire leans in turns, can an automobile tire be used or does it need a wide motorcycle tire ?

 

[AriLea]

if the rear tire leans in turns, can an automobile tire be used or does it need a wide motorcycle tire ?

A motorcycle tire will be slightly more compliant to oddball angles, and will not change the tire patch area as much. It is however already a smaller patch than what a car application provides for the same tire width. It maybe hard to find a motorcycle tire that is actually wide enough, if your gross weight is high.

But also the motorcycle tire was already not the best in a non-tilt application and not designed for fully horizontal side forces. So this can add subtle and odd over steering or maybe unexpected loss of traction (or road grip) in a high speed turn.

Car tires are designed to perform better with side-forces, but only up to a point. Once that tire patch is distorted enough, it may not be as compliant to the road as it was before. When that happens it can have the handling issues like those noted above. That is a very high bar that only racing and poorly design cars encounter. (or tikes with flimsy swing arms)

These dynamics are all more subtle affects in our FWD trike, than the same dynamics in a trike with power at the rear.

The combination of the tire patch area and expected loading puts a level of engineered PPSI matched to the rubber compound and performance expectation. Too light a loading and the tire will not conform to the surface or even the rubber will ride on top of the surface lifted by articulate mater such as sand or gravel. Too heavy of a loading then the tire geometry will distort, or the rubber will deform, which creates some wear and heat and also can add to other compliance oddities such as over-or-under steering etc.

Generally the motorcycle tire is engineered to allow more compliance and extra wear, traded for better traction (or road grip) and predictable handling. While the car tire expects to experience a more predictable geometry, but accepts higher changes in horizontal loading.
So yes, the car tire can not accept as much oddball tilting of the tire. But inside the dynamic envelope of a car tire's design you get better overall performance.

So then, just to give this more shades of grey, often the standard car tire (non-racing) has traded in some of that performance for longer tire wear or lower rolling resistance.

Without some good experimentation or tight engineering, it's better to stiffen the swing arm and go with a standard car tire.

More grey issues. Some trikes have a very wide tire at the rear, expecting the extra patch will make up for any possible losses, I guess. Or just to be cool. If very soft, this will accommodate compliance to the surface at a cost of high wear and wasted power. But when that tike tilts, the inside of the wide tread can possibly lift, then things may experience changes the driver can not anticipate. Like your line of expected travel suddenly shifting left or right in that turn. When you correct, it suddenly goes the other way. That is what shifting over-under-steering feels like.

 

[JEBar]

well, I'm sure glad that Mark has to deal with all that and all I have to do about it is to crank the engine, put the tranny in gear and head down the road ..

 

[Mark BEX]

I remain a little concerned about the swing arm.

I want to make it clear to everyone that Ari is 100% correct in his engineering foundations, concerns and recommendations for resolution, and appreciate the input. This is in fact my favorite part about internet forums, eg; having others input for views that I may not have seen, along with new ideas and methods of implementation that I may not have considered.

Note that race and sports motorcycle swingarms have been braced in this pyramid method for decades

From a real world perspective though, based on vehicle type, demographic and real world usage, I am far less concerned about twist/loss of contact area being an issue due to very light loads expected, and had intended to use a camera during testing to view what the rear wheel will be doing under various load conditions to see what additional bracing might be required, if any.

Also note that basic triangulation has yet to be added in the CAD drawing there, and is most certainly happening.

 

[AriLea]

I'm very sure Mark will refine the Bex design to a very satisfactory level.
I went by the local dealer in AZ who sells the Vanderhall, see below. This is a very-very light vehicle. 1.4L Engine. Wide and low rims. He also had a white one on hand. Also this gives me more context for the Blackjack Guzzi. They do look like fairly direct equivalents. I took a picture of the rear arm to compare with.
The hood area is wider than the Blackjack, as I expected, since it is a inline engine orientation rather than a sidewinder like the Venice.
(Sorry, slot-car terms from my youth.)

The card I set on top of the arm is 6in long(15cm).
They basically use a large cross-section arm, let's guess it's thin aluminum, casting, then welded halves. Unless they now do rotational molding for metals..(not likely, given how sand acts).
The tread was soft enough I think I could dig it out with my nails. Almost no channel relief for water. Yes it will hydro-plane.

 

[Mark BEX]

Today I got the laser parts for the rear swingarm mounts,

and did the front strut top mounts.

The strut mounts are finished, but able to be moved if need be after I check ride height later.

They basically use a large cross-section arm, let's guess it's thin aluminum, casting, then welded halves.

Bet you don't get change from say $1500 for that, mine would be under $150, using $15 worth of steel ..

 

[84mpg]

Mark.... I like how you’re thinking...

looking good so far....

 

[JEBar]

The strut mounts are finished, but able to be moved if need be after I check ride height later.

I'm looking forward to seeing what the ride height will be when everything is installed