Help me understand Pre-load

[Huzo]

 Peter , mate , if the spring is free to move upward , then increasing preload would have zero effect .

 Dusty

That is not true Dusty and just a touch condescending..
It will lengthen the overall eye to eye distance, therefore ride height.

[Ryan]

Read this. It will help. https://www.cycleworld.com/sport-rider/suspension-setup-guide/

[Huzo]

So increasing preload (compressing spring) with no weight on the seat will RAISE the ride height?

Contrary to reply #9, yes it will raise the ride height, as long as the shock has not “topped out” with the bike on it’s wheels (which should be the case..)
Remember the load on the spring from the effects of pre load and weight are not cumulative..
Once the shock comes off it’s stops under the effect of weight, then the pre load is irrelevant from the point of view of spring “stiffness..”

[Huzo]

Read this. It will help. https://www.cycleworld.com/sport-rider/suspension-setup-guide/

If you just confine yourself to the OP’s question, that should help.
To muddy the waters with discussion on damping before the concept of pre load os bolted down, is counter productive.

[Ryan]

Well, gee. The article defines it, how to set it, and why. But hey, sorry to muddy the waters.

[oldbike54]

 Huzo , technically it is the bottom of the shock that is free to move .

 Dusty

[rocker59]

That's why when you purchase a new motorcycle, the dealer should set the sag with the rider when the dealer delivers the bike  (I know you Guzzi guys won't spend for a new bike and only buy used).

How many "dealers" out there do you think know or understand enough about suspension to do that?

[kirby1923]

After being in this game for a while I'd say rare to none.

:-)

[Huzo]

Huzo , technically it is the bottom of the shock that is free to move .

 Dusty

Well, if we were talking about a standard pair of shocks like on a Breva 750 as an example, that would not be true would it ?
Raising the ride height lifts the top mount and takes the top of the spring with it..

[Huzo]

Well, gee. The article defines it, how to set it, and why. But hey, sorry to muddy the waters.

That’s a good thing to read Ryan, but my point about the mud was..
While there are guys digesting one concept, it clouds the issue to contaminate the discussion with more information.
But your teaspoon sized dose of thinly disguised  sarcasm is totally justified and understandable..
I just re read my #33 response and it had an edge to it that was not intended.
I could have phrased it better, the section on pre load was good.

[80CX100]

Read this. It will help. https://www.cycleworld.com/sport-rider/suspension-setup-guide/

Hey Ryan, Tks very much for posting that link, I'll take all the help I can get, especially if it's free (guzzi content).

I've downloaded a few suspension set up guides over the years, that is definitely one of the better ones 

It's filed away safely for future reference

Tks

Kelly

[LowRyter]

How many "dealers" out there do you think know or understand enough about suspension to do that?

Sit on the bike on the shop stand.  Then ask the tech to  crank the preload until it's about 1/3 compressed.  Put the other adjusters in the middle and make a test ride. Repeat until the sag is done.  Not rocket science.  The factory setup should give the approximate weight of the average rider, so it's pretty easy to know to go up or down as a start.  This much easier as two man job.  I think that's part of the set up fee.

Then it's up to the rider set the rebound and dampening.  I think starting full soft, and then experimenting with each separately perhaps half way & go for a ride, then do the opposite for the other setting.  That way the rider will feel what each adjuster does.  After that, work both adjusters in tandem.  It will take a few rides to dial it in. 

I'm not one that adjusts for every situation but I have to soften the fork on the Greenie when I put the HB Jr bags on, sometimes the shock but not so much since I determined the fork was my issue.  My other bikes are set it and forget it.

When I picked up my Duc, I asked them to set the sag for my weight (classified info).  It seemed spot on, whether they did it or not.  I've only taken a round of rebound off the rear for these bouncy Okla roads.

[oldbike54]

Well, if we were talking about a standard pair of shocks like on a Breva 750 as an example, that would not be true would it ?
Raising the ride height lifts the top mount and takes the top of the spring with it..

 Actually it pushes the swingarm down .

 Dusty

[pressureangle]

There are 3 distinct definitions that must be held separate to understand each.
1. Spring rate (pounds required to compress spring 1 inch)
2. Pre-load (the distance the spring is compressed while installed, at full suspension extension)
3. Sag (the distance suspension is compressed by the weight of bike and rider compared to full extension, or from static to 'with rider')

The *purpose* of 'sag', at it's core, is to allow outward travel of the suspension into depressions; everyone thinks about absorbing bumps, but rarely consider the holes. The 'perfect' sag is entirely dependent upon your riding environment and style. Where I am in South Florida, the roads are very smooth compared to most of the country. I don't require as much sag as in say, Detroit (lol) because the average roadway depression here is maybe 1/2 to 1" where in Detroit it's entirely expected to encounter 2-4" holes in the road.
Spring rate and pre-load are both considerations more of weight (and dynamic compression) than of road surface, and of riding requirements (pleasure + comfort vs. racing).

[Tusayan]

Actually it pushes the swingarm down

The swing arm can’t go down unless the ground moves, which it doesn’t.  The frame rises.

[oldbike54]

The swing arm can’t go down unless the ground moves, which it doesn’t.  The frame rises.

 The frame rises because the swingarm is pushed down .

 Dusty

[Tusayan]

Normally the coordinate system when discussing things rising or falling is considered to be fixed relative to the earth, not to the motorcycle.  The rear axle and swing arm do not change location relative to the ground.  The frame does rise relative to the the ground.  The motorcycle rises, it does not push the ground downward.

[oldbike54]

Normally the coordinate system when discussing things rising or falling is considered to be fixed relative to the earth, not to the motorcycle.  The rear axle and swing arm do not change location relative to the ground.  The frame does rise relative to the the ground.  The motorcycle rises, it does not push the ground downward.

 Exactly , it rises because as the swingarm is pushed down the frame has to rise .

 Dusty

[SmithSwede]

I’m surprised that nobody has discussed the fact that gyroscopic precession above about 35 mph typically causes a torque absess on most twin shock Guzzis that lack a non-Euclidean swingarm. 

So I wear all my gear, sit on the bike, and set pre-load to achieve about 1/3 sag.   

I figure that without a drawn reciprocation dingle arm, there is really no effective way to reduce the sinusoidal repleneration. 

So I do 1/3 sag and call it good. 

[oldbike54]

 It's true Norm , it's really true .

 Dusty

[80CX100]

I’m surprised that nobody has discussed the fact that gyroscopic precession above about 35 mph typically causes a torque absess on most twin shock Guzzis that lack a non-Euclidean swingarm. 

So I wear all my gear, sit on the bike, and set pre-load to achieve about 1/3 sag.   

I figure that without a drawn reciprocation dingle arm, there is really no effective way to reduce the sinusoidal repleneration. 

So I do 1/3 sag and call it good.

Finally someone explains it in simple layman terms   

 

[oldbike54]

I’m surprised that nobody has discussed the fact that gyroscopic precession above about 35 mph typically causes a torque absess on most twin shock Guzzis that lack a non-Euclidean swingarm. 

So I wear all my gear, sit on the bike, and set pre-load to achieve about 1/3 sag.   

I figure that without a drawn reciprocation dingle arm, there is really no effective way to reduce the sinusoidal repleneration. 

So I do 1/3 sag and call it good.

 Yes , and according to the theory of relativity , gravity pushes down .

 Dusty

[wirespokes]

And here I thought gravity sucked!

I disagree with the notion the frame is what moves and not the ground.

That's definitely the case with no suspension.

The objective is to keep the frame from moving up and down - the wheels should do all of that. That's what suspension is all about!

[Huzo]

Actually it pushes the swingarm down .

 Dusty

Closer to the road..?
I would have thought that the axle would always be the same distance from the road surface..
Does the tyre go below the level of the road..

[Huzo]

Exactly , it rises because as the swingarm is pushed down the frame has to rise .

 Dusty

Dusty..
I think you are purposely taking the piss and you got me..
As that great philosopher John Mc Enroe said...”YOU CAN’T BE SERIOUS..”
The distance of the axle to the ground never changes.....Think mate..
If I squat down then push down with my feet to stand up, I don’t succeed in pushing my feet down because they are on the ground, the equal and opposite force pushes me up.

[Huzo]

Yes , and according to the theory of relativity , gravity pushes down .

 Dusty

Well not actually according to the theory.
The lesser mass will be attracted to the greater mass, there is no “up” or “down..”
For Chrissakes Dusty, go back to talking sense and put this into “Thread Drift..”

[Huzo]

The frame rises because the swingarm is pushed down .

 Dusty

The bleedin’ obvious Dusty..
So does cranking on pre load actually MOVE the axle downward or not.
A one word answer of two or three letters will suffice.
It will start with a “Y” or an “N”...
And then we’ll know which of your comments to delete..

[kingoffleece]

If my understanding is correct Dusty is correct.  My engineer friend informs me that this is sometimes called a paradox-in where an observed "issue" is thought to be one thing due to 'commom knowledge" but in fact is some other.  While the observation may be the bike is raising-in fact it is changing due to the force exerted into the ground.

Thing of a space station in orbit.  It's falling at a constant rate and, to keep it VERY simple, stayes in it's relative orbit as the earth is "falling" away at the sdame constant rate.  Yes, there are other factors but this is the basic concept.

The notion of "oversprung and underdamped" is spot on.  That's the defination of a cheap shock, which almost every OEM can claim.

[oldbike54]

 Effectively a spring is a lever that can apply force in two directions . Thing of the human arm which is also a lever arm like early Moto Guzzi suspension or the lever style shocks used on some British cars . What happens when you do a push up , where is the force being applied ? Now turn over on to your back and make the same arm motion involved in a push up . What happens , nothing , right ?

 Dusty

[Huzo]

Dusty...
A lever is a beam that operates through a fulcrum or pivot, a spring is an expanding mechanism releasing stored energy.
If the bike sails across a depression in the road then yes, the axle will be pushed “downward” in the accepted sense to maintain contact with the surface. But we are talking about winding on preload with the bike static and at rest, so to suggest that this results in pushing the swing arm down, is a touch infantile and ill advised.
KOF I really do love you


But mates or not, if you read Dusty’s assertion word for word..?
He’s not correct.
He SAID... “it pushes the swing arm down...” BS
He SHOULD have said...”it pushes down on the swing arm..” Yes.
Tusayan understands..(as usual..).
And KOF mate..

Analogies about falling space stations while well intended, are a bit of a flight of fancy into uncharted waters of tangential argument, full of more holes than Swiss cheese..
Sound engineering principles with correctly applied terminology will be more likely to win the day...