In article ,
says...

Cross-Slide wrote:
On Oct 4, 8:00 am, "Snag" wrote:
Karl Townsend wrote:
I'd settle for a set of sketches of the geometry ... the budget on
this one is "do it yourself or you can't afford it" .
We've decided to sell her Kawasaki since she's just not all that
hot on leaning into turns , and my budget is whatever I can get for
it . Probably somewhere in the $700-$900 range - which will buy the
materials (I hope !) .

If you're rolling yer own...

Can you start with a shaft drive bike? (That would not be the Honda
750, its chain drive) Then take the smallest rear wheel drive car
you can find for drive and suspension parts.

I've seen a few people that can just do this. For most it would be a
nightmare to design.

Karl

Well , the thing is that I already have the CB750 , and it's paid
for .
Got some ideas for casting a housing for the diff out of aluminum I
have on hand ... start with a lost-foam casting , or maybe make a
wood pattern that I can alter for offset depth to accomodate the
sprocket , since it's off-center . Might be able to incorporate a
single 4-pot caliper on the diff housing , that'd simplify things a
lot too .
Ideas , ideas , streaming thru my head ... I had a hard time getting
to sleep last night .
--
Snag
Wannabe Machinist

Pay close attention to the "Roll Center" of you suspension.
It is what made the Beetle, and the Corvair so "Exciting" to drive.

With a four bar linkage, the links point off into space to the
"reaction point" that imaginary point where the linkages intersect off
in space. THAT is the (instantaneous) point where the wheel pivots
around as it moves up and down.
As the wheel moves up and down that point in space moves too.

You can draw a line from the point of contact on the road to that
instantaneous center and where it crosses above or below you center of
mass is the Roll Center.
If the Roll center gets too high, it tries to jack up that corner of
the vehicle, and tuck that tire underneath. That is wha the Beetles
and Corvair did in a hard corner.

They basically swiveled the rear axle shaft from a single U-joint on
the trans-axle, and that became the Roll center.

If you look at a Corvette or a Jaguar independent suspension, they
have two u-joints and the roll centers are established by the
linkages. The instantaneous center can be anywhere, as set by the
geometry of the linkages.

A Front wheel drive will typically use McPherson struts with a single
lower A arm. That might not be acceptable for your layout. So, finding
the appropriate uprights will be one of the many tricks, or problems
to solve.

Another consideration will be camber gain/loss as the suspension
travels.
And any amount of bump steer. (!)
If on the front of a vehicle, a wheel hits a bump, and that for
example causes that wheel to turn towards the center line, the car
will react as if it is going into a turn, And exaggerate the bump, and
exaggerate the unintended turn, etc.
The vehicle will dart about on a bumpy road.
For example, the right front tire turns so very slightly to the left
as it hits a bump, and visa-versa. The vehicle will dart and skitter
over bumps or ripples. If the wheel bump steers in the other direction
it will be more stable.
This is also important in the back of the vehicle.

There is also anti-dive built into suspension. The brake reaction
torque on the front end will try to make it rise slightly, to overcome
the tendency to nose-dive on braking. This is a function of the front
end A-Arm geometry.
This also affects the rear end.

I don't have enough life expectancy to spend it re-typing several
entire books here.
But there are some important considerations. It is not too complicated
once you understand the principles.

It is no more complicated than understanding gear ratios before you
set out to design or build a transmission from a stack of totally
random gears. You would need to understand ratios, ratio spreads and
other stuff to make it work. But you at least have to know something
about it before you started to make it work "acceptably" the first
time.

Getting a suspension system nearly correct might be perfectly fine
until you hit that first pothole with the wrong wheel while going
around a corner, with just a little mist on the road.......

This might a good place to start.
http://www.carrollsmith.com/books/

I hit a website Sat. night that explained all this you've said in great
detail . And that's the reason I choose to use an unequal length a-frame
type of suspension . I can build in the proper camber characteristics , set
the drive components so there's no "zero movement" in the CV joints , and of
course set it up so the instantaneous roll center stays close to or below
the center of mass . I'm still studying , and will not cut the first chunk
of steel until I'm satisfied that my design will do what I intend it to do .
The woman I love will be ridin' this thing , should it ever come to more
than just talk . And you can bet your sweet a$$ I'm going to make sure she's
as safe as I can possibly make her .
My first car was a '62 Pontiac Tempest , used that infamous Corvair
transaxle that Ralphie got in such a tizzy over . You're right , it was
unsafe under certain conditions . But it left the coolest burnouts ...

Have you seen "My Cousin Vinnie"? If not, I think you might want to.
After you've seen it you'll know what made me think of it.