Cheap Rear Suspensions with Adjustments

 My little Honda Shadow has, as best I can tell, a combined spring and shock
thingie.  You put a spanner tool in and are able to rotate a ring on it.  It
has 7 positions.  The upper end is connected to the frame, and the lower end
to the swingarm.

Questions:

#1)What does the adjustment do exactly, and how does it do it?

#2)How should one adjust it (any rules of thumb about what the right
position is)?

Thanks, The Lizard

 Jujitsu Lizard wrote:

It's spring preload.  By turning that adjustment, you shorten the
spring, pre-compressing it.  More compressed = harder ride.


Make sure both sides are equal.  If you're hitting bumps that make the
shocks bottom out, put it up a notch.  RTFM, it probably will give you
some basic guidelines.

 Outback Jon schrieb:


Sorry, wrong. The spring stays exactly as hard as it is because this
is determined by the spring rate, a material constant.

The only exception may be a progressive spring where you compress the
soft bit first by tightening the preload.

What you in fact change is the amount the bike sinks in when you mount
it.

This is important because if there's not enough, the wheel might lose
traction on the rebound after a bump.

The rule of thumb for preload adjustment is that there should be about
70 per cent of wheel travel left when loaded with the complete
payload.

--

Gruß
Radbert

 

It pushes the collar against the spring, preloading the spring.

Suppose you have a single shock with 3 inches of travel. The single
spring has a rate of perhaps 250 pounds per inch.

So 3 X 250 = 750 pounds of weight that the spring will support without
compressing completely.

By turning the ramped collar you preload the spring perhaps 1/4 of an
inch more for each click, so there is only 2.75 inches of shock travel
left, the spring is supporting the same weight as before, but the
spring raises the seat height a bit and the shock absorber now has to
operate at a slightly different *ride height*.

The damping mechanism inside the shock will be working at a different
point in its stroke, so the damping action will be slightly different.


Just sitting down on your Shadow should cause the rear suspension to
compress about 1/3rd of the total travel.

It's OK if your rear suspension occasionally bottoms out on the worst
bumps, but you don't want your *front* suspension to ever bottom out
when you hit a bump while going around a curve because the motorcycle
will run wide of the corner if the forks bottom out.

Ride the motorcycle on the highway, around a curve of large radius. If
you are observant, you'll notice that a softly-suspended motorcycle
does a dutch roll, yawing and pitching and rolling all at the same
time.

Stop and add one more click of preload and ride the same curve again,
repeating the process until the dutch roll is gone.

Suspension engineers who have studied the wallowing motions have
determined that when the suspension oscillates at only 1 cycle per
second, the rider feels
nauseous, it's as if he was in a boat at sea, experiencing wave
action.

Increasing the spring preload affects the natural frequency of the
spring.

3 cycles per second oscillation makes the motorcyle feel much more
controllable, but 5 cycles per second makes the ride so rigid the
rider's eyeballs jiggle and he cannot focus on the road.

 
I remember a year or two back I bottomed out the rear and I added a couple
notches.  I think the spring preload is now up to 5 of 7.  I didn't know
what I was doing, but it seemed to have improved the ride.

I understand the technical aspects of what you've written, but I've never
noticed any oscillation on the bike at any frequency.  The front suspension
does its job.  Once in a while I look down and can see that the suspension
is moving just do to imperfections in the road, but I don't notice anything
other than that.  On the rear, I feel it compress and relax when I go over a
bump ... but I've taken lots of curves on 2-laners at highway speeds and
never noticed any oscillation.

I may just not be observant enough.

The Lizard