Setting Proper Sag

[docc]

Still seems like the first few mm will compress identically to the last few mm ( just as in increasing preload) as long as the spring rate in linear ( non-progressive).

 

And in the algebraic vernacular, if 'bike only' is B and 'bike and rider' is BR, then BR-B=R (rider), no?

 

Honestly, this is semantics and no doubt the difference between laden and unladen sag is as important as the sag measures themselves. I think the 18mm+/- measure is a good figure and agree that the Sport behaves better (subjectively) with more unladen sag front than rear, yet with a smaller 'difference' ( or whatever we're calling the difference) up front.

 

Still no thoughts on optimal preload? Traxxion specifies adding 15mm for the fork springs, but wouldn't that depend on the free length of the spring and its full travel?

[Guest ratchethack]

And in the algebraic vernacular, if 'bike only' is B and 'bike and rider' is BR, then BR-B=R (rider), no?

No. See post #30, now updated for (hopefully) greater clarity.

 

Sorry, the idea of "optimal preload" escapes me. IMHO, even assuming identical sags and bike weights, two different weight riders will use different preloads to achieve target sags, independent of spring rate. The idea of "optimal preload" is every bit as vaporous as "rider only sag" -- in other words, as fleeting as the fabled chimera.

 

Neither concept is a semantic triviality, my friend. There are unpleasant consequences for confusion.

 

If I were completely heartless and cruel, I'd refer to "Exhibit A". But of course, I'm anything but that. . .

 

IMHO, preload isn't one of those "guideline" kinds of parameters like sags. It's more of a "supporting role" kinda concept.

 

BAA, TJM, but I seriously doubt if y'er M is likely to V.

[Skeeve]

Now THAT oughtta drive a solid point home somewhere (so to speak) . . .

 

Mind if I borrow that one, Skeeve?

 

Help yourself: all my best material is stolen anyway, so if someone wants to use one of my [pitifully few, unfortunately] own gems, I can hardly complain!

 

Your post was well expressed, IMHO.

 

Thanks, I'm quite flattered you think so! Coming from someone who can clearly express mathematical arguments such as the one above (in thread), that's a real compliment.

 

Still & all, I must admit to being King of the Procrastinators [or rather, would be, if I could ever get around to running for the office] & tend to put off the necessary changes & live w/ the cr@ppy ride & ill-handling. I think my SV was the 1st bike that I ever went the distance & changed the fork springs on simply because I knew how much better it could be, given that even on forks that had a laden sag of 2/3 the total travel it was the best handling bike I'd ever ridden to that point! [c.1999]

 

Hence my interest in getting my LeMans dialed in: I expect to keep this bike 4EVA!

 

[Guest ratchethack]

Still seems like the first few mm will compress identically to the last few mm ( just as in increasing preload) as long as the spring rate in linear ( non-progressive).

You're right Docc. I had to put my "straight rate" thinking cap on, then I changed my previous post.

 

Really, there's so little difference between the rate curves on progressives and straight rates anyway, that IMHO they don't make all that much real-world difference on the road, but I prefer them as a general rule, being on my 3rd bike with progressive fork springs now. IMHO, used in forks, they're well matched to rising rate linked rear suspensions.

 

BAA, TJM, & YMMV

[Skeeve]

NOTE: Many of the suggested guidelines for setting sags incorporate pillion passenger considerations. This not only skews the suggested sag ranges, but opens up the range of acceptability a great deal more on the rear, in ways that many solo riders (myself included) would not find acceptable. Since most riders (myself included) seldom ride 2-up, it should be noted that solo set-up guidelines for front and rear sags are significantly closer than for 2-up riding.

 

This is an instance where "using preload to adjust for rider wt." is acceptable & reasonable. Let's use the 80/20 rule: 80% of your riding is done solo, & only 20% two-up. Should you use a spring rate that was biased 80% of the way towards the correct 1-up spring rate? Of course not: you'd still have an unreasonably harsh ride all the time, since it will still be 20% oversprung at the lightest (nonexistent) preload setting, & yet undersprung for 2-up riding to the point where the preload necessary to compensate will still deliver a harsh ride over small bumps yet be insufficient for the really big ones.

 

What to do?

 

Easy: get the springs dialed in for the solo rider. Absolutely, 1st order of business every time. When riding 2-up, add enough preload to get the laden sag back in the correct range. That's *all* you can do. You'll end up with a really soft, plush ride [like the Gold Wings I mentioned earlier, only those were too softly sprung even 1-up!] The passenger doesn't have to know how hard you're working to avoid any really bad bumps or potholes in the road, and the loosey-goosey feeling you're getting from the handling is your reminder to dial it back a notch or two & SLOW THE HECK DOWN & enjoy the ride (& btw, save your lives.)

 

Much of this has gotten terribly repetitive. It's a sign that this thread is losing steam. I'm losing interest anyway, so I assume most everyone reading has already bailed. [sigh]

 

I'm still here... [& did I forget to mention, I have a notoriously short attention span?]

 

Play on!

[Guest ratchethack]

. . .my interest in getting my LeMans dialed in: I expect to keep this bike 4EVA!

 

One o' the best motivators and/or justifications I can think of meself.

 

I figure it this way: If you're going to own a Guzzi -- especially 4EVA, best take advantage of the handling capabilities it was designed with. Unless and until you set it up properly, you'll never have much of a clue. . .

[dlaing]

Along the same conceptual lines, I thought of a way to hopefully de-confuse Dave, as soon as he makes his way back to an unsupervised screen. . .

 

ASSUMPTIONS:

 

Front and rear target sag measurements are kept the same for correct fore-aft chassis balance.

 

In setting up the sags, a 2:1 laden-to-unladen ratio (in mm) will be maintained as closely as possible by adjusting preload accordingly.

 

For general purpose guidelines, 15% of total avaliable suspension travel (120 mm) = unladen sag = 18 mm.

 

For GP guidelines, 30% of total available suspension travel = laden sag = 36 mm.

 

For GP guidelines, an 18 mm +/- 5 mm difference in sag measurement is about right.

 

Let R = rider weight

 

Let G = Guzzi weight

 

Let R + G = combined rider and Guzzi weight

 

Let A = unladen sag, measurement in mm of Guzzi only. A varies inversely with spring rate and directly with load.

 

Let B = laden sag, measurement in mm of Guzzi and rider. B varies inversely with spring rate and directly with load.

 

Now then.

 

R (in lbs.) determines A (in mm)

 

R + G (in lbs.) determines B (in mm)

 

IF:

 

B - A = 18 mm, +/- 5 mm

 

AND:

 

B - A = D (or the difference in mm between B and A in mm). D varies inversely with spring rate and directly with load.

 

THEN:

 

Spring rates, front or rear, will always be correctly matched to D, regardless of rider weight.

 

D is not altered by a change in rider weight as long as spring rates are accordingly changed to match load.

 

THEREFORE:

 

D, like total avaliable suspension travel in mm, correctly remains a constant for every rider of a given weight, regardless of what that weight is (within normal human weight variance), as does the total avaliable suspension travel. D is slightly variable around this constant (+/- 5 mm or so). D is properly related to total available suspension travel for riders of all weights, all abilities, and all preferences. It is only by maintaining this constant that a full and proper range of correctly loaded suspension travel may be realized, by intent of the engineers who design both the bike and the suspension components.

 

-- Prof. Hatchracket, GPh.D., Esq.

Nice clear way of laying it out.

The only problem is that you are misleading when you said,

"Let A = unladen sag, measurement in mm of Guzzi only. A varies inversely with spring rate and directly with load."

By adding preload one can make unladen sag equal 0mm, or by completely removing preload one can make it sag as much as the bike's weight forces it.

So if you are relying on the A to calculate B-A=D, you are going to get a BAD result

 

Increasing preload on too light of a spring only leads to a harsh ride over small, sharp bumps that still bottoms over larger ones.

Excellent point!

I suspect Ratchet will soon see the light and realize that his "A" measurement is distorted by the preload, and that he is misleading Sumo Sammy and Willie Shoemaker.

But Ratchet is not alone in misleading.

Most sag guides are an over-simplification. Luckily most of the time the over simplifications work well enough.

I just think we can go better that simply saying everybody should set both front and rear to 15/30% ±5mm difference between laden and unladen.

[BrianG]

 

 

By adding preload one can make unladen sag equal 0mm, or by completely removing preload one can make it sag as much as the bike's weight forces it.

So if you are relying on the A to calculate B-A=D, you are going to get a BAD result

 

 

Wrong....... preload does nothing but determine ride height for any give weight (rider or not).

 

...........unless you wind it up so tight that the shock/fork tops out, which is just dumb.......

[dlaing]

Still no thoughts on optimal preload? Traxxion specifies adding 15mm for the fork springs, but wouldn't that depend on the free length of the spring and its full travel?

I am glad you brought up optimal preload.

I have not read anything at all clear on that.

We do know that too much preload is a very common and often bad problem.

But what is too much?

The Willie Shoemaker example I gave would be too much.

The Sumo Sammy example would be too little.

Perhaps it is all much ado about nothing and all of us 150-250# riders will be fine within any of the experts ranges.

Certainly bikes ship well out of those ranges and at the very least it is an easy improvement.

[dlaing]

Does this help:

 

http://www.sportrider.com/tech/146_0308_geek/

 

This is how it was done on my Aprilia Falco. Great results.

It is a good clear article, and the coverage on how to measure and correct for errors due to stiction is excellent.

But it over-simplifies the process by not discussing unladen sag at the front.

And like all of the expert writings, it does not go in deep into variations of bikes and riders and preferences.

They suggest 25-30mm laden front and rear.

And they suggest 5mm unladen rear.

So, these experts suggest ~ 4%/22-25% not 15%/30% at the rear.

 

 

Wrong....... preload does nothing but determine ride height for any give weight (rider or not).

 

...........unless you wind it up so tight that the shock/fork tops out, which is just dumb.......

Wrong.

Preload does much more than that.

It F's up your ride if too much or too little and it F's up Ratchet's math as he tries to determine proper spring rate for people all over the globe.

[dlaing]

Still seems like the first few mm will compress identically to the last few mm ( just as in increasing preload) as long as the spring rate in linear ( non-progressive).

Not completely true.

It may be a case of splitting hairs, but there is some progressiveness even when using straight rate springs.

But generally we can ignore it.

My measurements could be a little off but here is what I got when I installed my Penske with 550# spring

~8 turns preload:

unladen 21mm

laden 50mm

difference 29mm (the effect of only the rider's weight)

I then added ~10 more turns of preload and got:

unladen ~5.5mm

laden ~31.3mm

difference 25.8mm

I suspect the change in difference between 29 and 25.8mm is due mostly to the gas in the shock.

Again predictability goes out the window

FWIW Penske recommends laden sag between 7/8" and 1-1/6" (22.2mm and 29.6mm)

So, by there recommendation I should add preload or get a firmer spring to reduce sag at least ~1.7mm to get within their range.

But I don't want to reduce unladen sag at all. 5.5mm is small enough!

I am pretty sure the HyperPro rising rate spring would improve the ride and better match the front. ...someday.

[g.forrest]

It is a good clear article, and the coverage on how to measure and correct for errors due to stiction is excellent.

But it over-simplifies the process by not discussing unladen sag at the front.

And like all of the expert writings, it does not go in deep into variations of bikes and riders and preferences.

They suggest 25-30mm laden front and rear.

And they suggest 5mm unladen rear.

So, these experts suggest ~ 4%/22-25% not 15%/30% at the rear.

Wrong.

Preload does much more than that.

It F's up your ride if too much or too little and it F's up Ratchet's math as he tries to determine proper spring rate for people all over the globe.

 

 

FWIW a whole lot of crap abought just go learn to ride a and stop making excuses for lack of control or lack of ability.

[dlaing]

FWIW a whole lot of crap abought just go learn to ride a and stop making excuses for lack of control or lack of ability.

Who is making excuses?

Few of us are out racing.

But alot of us are trying to help people better set up their V11s.

Why don't you go tell slow kitty to forget all about why the Guzzi handles like crap and to go learn to ride?

Would that be a responsible thing to do?

[dlaing]

Along the same conceptual lines, I thought of a way to hopefully de-confuse Dave, as soon as he makes his way back to an unsupervised screen. . .

 

ASSUMPTIONS:

 

Front and rear target sag measurements are kept the same for correct fore-aft chassis balance.

 

In setting up the sags, a 2:1 laden-to-unladen ratio (in mm) will be maintained as closely as possible by adjusting preload accordingly.

 

For general purpose guidelines, 15% of total avaliable suspension travel (120 mm) = unladen sag = 18 mm.

 

For GP guidelines, 30% of total available suspension travel = laden sag = 36 mm.

 

For GP guidelines, an 18 mm +/- 5 mm difference in sag measurement is about right.

 

Let R = rider weight

 

Let G = Guzzi weight

 

Let R + G = combined rider and Guzzi weight

 

Let A = unladen sag, measurement in mm of Guzzi only. A varies inversely with spring rate and directly with load.

 

Let B = laden sag, measurement in mm of Guzzi and rider. B varies inversely with spring rate and directly with load.

 

Now then.

 

R (in lbs.) determines A (in mm)

 

R + G (in lbs.) determines B (in mm)

 

IF:

 

B - A = 18 mm, +/- 5 mm

 

AND:

 

B - A = D (or the difference in mm between B and A in mm). D varies inversely with spring rate and directly with load.

 

THEN:

 

Spring rates, front or rear, will always be correctly matched to D, regardless of rider weight.

 

D is not altered by a change in rider weight as long as spring rates are accordingly changed to match load.

 

THEREFORE:

 

D, like total avaliable suspension travel in mm, correctly remains a constant for every rider of a given weight, regardless of what that weight is (within normal human weight variance), as does the total avaliable suspension travel. D is slightly variable around this constant (+/- 5 mm or so). D is properly related to total available suspension travel for riders of all weights, all abilities, and all preferences. It is only by maintaining this constant that a full and proper range of correctly loaded suspension travel may be realized, by intent of the engineers who design both the bike and the suspension components.

 

-- Prof. Hatchracket, GPh.D., Esq.

Let us plug into your equation Sumo Sammy 250Kg rider and Willie Shoemaker 50Kg rider and assume h bike weighs 250Kg.

 

First Willie Shoemaker

Let R = 50kg (assuming weight is directly over axle for simplictity)

 

Let G = 125kg (half of 250kg assuming 50/50 weight split for simplicity)

 

Let R + G = combined rider and Guzzi weight 175kg

 

Let A = unladen sag, measurement in mm of Guzzi only. A varies inversely with spring rate and directly with load.

 

Let B = laden sag, measurement in mm of Guzzi and rider. B varies inversely with spring rate and directly with load.

 

Now then.

 

R 50kg determines A (in mm) If the spring deflects 18mm we can assume the spring at the rear is about 100kg/18mm or since 18 goes into 100 5.555555555555 times the required spring would be 5.5kg/mm (the swing arm is at about a 2:1 ratio, so 50kg must be doubled to obtain the estimated THEORETICAL spring rate at the rear. At the front it would be halved to 25kg/18mm since there are two fork springs.)

 

R + G 175kg determines B (in mm) (here is Ratchet's mistake. The weight alone does not determine the laden sag here. The weight and the preload determine the laden sag of a given spring, but to humor the three people are actually reading this far, the 175kg would deflect the 5.5kg/mm spring about 64mm if no preload was added. If you add preload you would need ~28mm of preload to bring it to the magic 36mm.

 

 

 

Looking at Sumo Sammy

 

Let R = 250kg (assuming weight is directly over axle for simplictity)

 

Let G = 125kg (half of 250kg assuming 50/50 weight split for simplicity)

 

Let R + G = combined rider and Guzzi weight 375kg

 

Let A = unladen sag, measurement in mm of Guzzi only. A varies inversely with spring rate and directly with load.

 

Let B = laden sag, measurement in mm of Guzzi and rider. B varies inversely with spring rate and directly with load.

 

Now then.

 

R 250kg determines A (in mm) If the spring deflects 18mm we can assume the spring at the rear is about 500kg/18mm or since 18 goes into 500 ~28 times the required spring would be 28kg/mm (the swing arm is at about a 2:1 ratio, so 250kg must be doubled to obtain the estimated THEORETICAL spring rate at the rear. At the front it would be halved to 125kg/18mm since there are two fork springs.)

 

R + G 375kg determines B (in mm)the 375kg would deflect the 28kg/mm spring about 27mm if no preload was added. If you add preload you would need ~9mm of preload to bring it to the magic 36mm.

 

So one has 9mm and the other 28mm of preload but it is all theoretical.

Still it proves you are not getting the same resulting 'ride' following the 15/30% rule. Although Ratchet and Company will deny it to the grave.

 

I am about twice Willie Shoemaker's weight and probably have about 30mm of preload and it is not bad.

In the real, non-theoretical world, I suspect a very light rider following the 15/30% rule would end up with too much pre-load, and the Sumo Sammys too firm of a spring.

 

YMMV but I'll continue recommending what the experts suggest, modified by rider weight and preferences.

[g.forrest]

Who is making excuses?

Few of us are out racing.

But alot of us are trying to help people better set up their V11s.

Why don't you go tell slow kitty to forget all about why the Guzzi handles like crap and to go learn to ride?

Would that be a responsible thing to do?

 

 

because it's long gone past answering slowkittys question, which is obviously not just a sag setting. and is once again you and ratchit trying to outdo each other with your theories. surely you's must both be aspiring politicians to waffle on so long without any real substance. i hope slowkitty can find an answer, but it won't be from all that crap!