Setting Proper Sag

[docc]

 

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.

May I suggest:

 

The mass of G determines A for any given spring rate and preload, rather than R?

 

Certainly there is a point where too much preload has been added to compensate for a soft spring. I found this to limit rebound compliance and believe it contributed to my crash. Better rebound compliance may not have saved me from the stupidity and lack of skill that caused the crash, but I could sure have used a little more help from the suspension.

 

That there can be too much or too little preload suggests that there would be an ideal that optimizes both the compression and rebound action of the spring.

[Guest ratchethack]

. . .stop making excuses for lack of control or lack of ability. . . .

Now let me see if I've got this straight.

 

REAL RIDERS have ABILITY and CONTROL! They don't NEED to understand anything about setting up suspension. They just ride it!

 

Forget all the adjustments and settings. They don't do anything anyway.

 

If a bike wallows, weaves, head-shakes, wobbles, washes out, bottoms, runs wide, or pogo's off the road out of holes, the rider is a spineless d!ckweed and doesn't know how to ride.

 

Anyone who wastes their time fiddling with numbers, swapping springs and spacers is an idiot.

 

A bike's handling capability is rightfully determined by the sloppiest suspension settings that ignorance and neglect can provide.

 

Dimwits who fiddle with their suspensions because they don't know how to ride are attempting to hide their inadequacy by trying to impress others with meaningless drivel.

 

Have I got it right now, Forrest?

[dlaing]

Now let me see if I've got this straight. <_>

 

REAL RIDERS have ABILITY and CONTROL! They don't NEED to understand anything about setting up suspension. They just ride it!

 

Forget all the adjustments and settings. They don't do anything anyway.

 

If a bike wallows, weaves, head-shakes, wobbles, washes out, bottoms, runs wide, or pogo's off the road out of holes, the rider is a spineless d!ckweed and doesn't know how to ride.

 

Anyone who wastes their time fiddling with numbers, swapping springs and spacers is an idiot.

 

A bike's handling capability is always determined by the sloppiest suspension settings that neglect and ignorance provides.

 

Dimwits who fiddle with their suspensions because they don't know how to ride are attempting to hide their inadequacy by trying to impress others with meaningless drivel.

 

Have I got it right now, Forrest?

[BrianG]

 

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.

 

This is why Ratchet is tired of arguing with you......

 

If you can't figure out this basic issue, you can have no possible idea of the rest of suspension dynamics.

 

I recommend that you fully investigate my statement and when you can discuss a REASON rather than just state an OPINION you could move forward.

 

For the present you are just messing up other forum members with your drivel...

[dlaing]

May I suggest:

 

The mass of G determines A for any given spring rate and preload, rather than R?

 

How did I miss that.

I thought Ratchet meant just that.

I guess I totally missed it when he wrote that the rider weight would determine unladen sag.

Of course it is the bike weight!!!!

Must have been a typo by Ratchet.

[Guest ratchethack]

May I suggest:

 

The mass of G determines A for any given spring rate and preload, rather than R?

Well, at least SOMEONE paid attention! Good eye again, Docc!

 

A mis-type, which I have corrected. Thanks.

 

I can't do this thread anymore. It's officially gone well past my attention span.

 

My 18 mm +/- 5 mm sag difference guideline is simple, works well enough for most riders IMHO, myself included. IMHO it's practical enough and accurate enough to transform the typically poorly set up and mediocre-handling Guzzi into a bike that stands out from the rest in both ride and handling, and manages even the most challenging terrain on the road with great confidence, and generally makes riding much more of a pleasure.

 

Hope somebody learned something helpful --eh, Forrest?

[dlaing]

For the present you are just messing up other forum members with your drivel...

No, you are messing them up defending Ratchet's misleading notion that ideal sag numbers don't vary relative to rider weight or more precisely the ratio of bike to rider weight.

I have proved it mathematically but you are too dense to get it.

Do I need to take it to a more absurd level?

Ok let us make the rider really light and put a 2.34489796kg remote controlled robot with camera onboard in place of the rider.

 

Q. How much is that going to deflect the spring?

A. not much.

 

Q. if it deflects the spring not much, how soft of a spring are you going to need to get the 1kg to deflect the spring 18mm?

A. really phreaking soft.

 

Q. If the spring is really phreakin' soft, how is the bike going to handle?

A. like crap.

 

Q. What would the proper sag numbers be for a set up like this?

A. Probably for the rear about 25%unladen and 25.1%laden sag. The front maybe 30%unladen and 30.1% laden. Sorry but the 15/30% would make the bike handle like crap. Because of the excessive preload, it would be harsh ride yet it would bottom out because the spring is too darn soft.

 

Q. Do you understand yet?

A. Not much chance as you are programmed by group think.

 

Well, at least SOMEONE paid attention! Good eye again, Docc!

 

A mis-type, which I have corrected. Thanks.

 

I can't do this thread anymore. It's officially gone well past my attention span.

 

My 18 mm +/- 5 mm sag difference guideline is simple, works well enough for most riders IMHO, myself included. IMHO it's practical enough and accurate enough to transform the typically poorly set up and mediocre-handling Guzzi into a bike that stands out from the rest in both ride and handling, and manages even the most challenging terrain on the road with great confidence, and generally makes riding much more of a pleasure.

 

Hope somebody learned something helpful --eh, Forrest?

I'll admit following your guidelines, it will be a lot better than it was when the bike shipped for 90% of riders.

I hope if Forrest ever gets a V11 he'll set the sag properly, whatever properly is...

Glad I gave the warning about possible diatribe.

[docc]

 

 

. . . the rider is a spineless d!ckweed and doesn't know how to ride.

 

 

Hey! I resemble that remark!

[dlaing]

QUOTE(docc @ Jul 18 2007, 06:47 PM) *

 

. . .sag: unladen /laden/difference - rear, 8/29/21 (18+3); front, 23/37/14 (18-4).

 

Outstanding, Docc. This is very close to wot I've got (give or take a few mm here & there and about 5-6 mm less preload on the fork),

So that means you are at about

REAR

8mm 7% unladen

29mm 24% laden

21 17% difference

FRONT

28mm

42mm

14mm difference

I think you are beginning to see the light

But I think that is too little preload in the front.

I think if you try Docc's numbers you will be pleasantly surprised.

Just don't ride like him or me.

[dlaing]

Now that Ratchet has seen the light, I believe that a consensus can be reached here is my black magic target sag number calculator for your typical Guzzi V11 with 80kg or 175# sport touring rider.

Believe it or not, I paid respect to group think and bent the numbers towards those numbers of Brian and Ratchet, believers of 15/30% front and rear. And I cut the modifier for rider weight in half of what I expect would be the accurate modifier. I am losing my individuality by compromising!!!

 

REAR Sachs

10mm unladen 8.3%

30mm laden 25%

FRONT

20mm unladen 16.7%

35mm laden 29.2%

 

MODIFIERS (all are rough guesses or opinions...what is your's)

*Racing, subtract 1 to 5 mm from laden sag.

*Touring, add 1 to 5 mm to laden sag.

*Frequent two up, subtract 1 to 6 mm from rear laden sag, and subtract about half of that from front sag. Note: this is assuming sag is measured without passenger.

*Ohlins, add 5mm to rear laden sag.

*Progressive springs, add 2mm to laden sag and subtract 1mm from unladen sag.

*Short legs, add laden and unladen sag at a ratio of maybe 4mm additional laden for every 5mm additional unladen. (because shock needs to be firmer as travel decreases)

*Rider weight greater than 80kg, add 1mm rear laden sag for each additional 20kg, and 1mm front laden sag for each additional 40kg

*Rider weight less than 80kg, subtract 1mm rear laden sag for every 20kg less than 80kg and subtract 1mm front laden sag for every 40kg.

*Personal preference, (no sag nazis here) add or subtract whatever you want to laden and or unladen sag numbers.

[BrianG]

 

 

Q. How much is that going to deflect the spring?

A. not much.

 

Q. if it deflects the spring not much, how soft of a spring are you going to need to get the 1kg to deflect the spring 18mm?

A. really phreaking soft.

 

Q. If the spring is really phreakin' soft, how is the bike going to handle?

A. like crap.

 

Q. What would the proper sag numbers be for a set up like this?

A. Probably for the rear about 25%unladen and 25.1%laden sag. The front maybe 30%unladen and 30.1% laden. Sorry but the 15/30% would make the bike handle like crap. Because of the excessive preload, it would be harsh ride yet it would bottom out because the spring is too darn soft.

 

 

Well, you were getting close until you got stupid with your example.......

 

Basically........ ideal laden sag is 30% of suspension travel. That is the point at which the suspension can be the most compliant with 2/3 of travel available for bumps and 1/3 for depressions.

 

The only thing that will affect the sag ratio for any ONE GIVEN WEIGHT is the spring rate.

 

Adjusting preload for ONE GIVEN WEIGHT will do nothing more than shift the ride height along the shock/fork length.

 

IF that were the only issue you could place the LADEN RIDE HEIGHT at 30% (or whatever) with any spring.

 

To resort to your tactic of extreme example..... lets say that the shock had a 2kg spring mounted. IF you wound up the preload high enough on this coil-bound spring you could get to the 30% point, but how would it ride? No compression motion and a soft 30% rebound that would slam back to coil-bind.

 

The suggested 15%/30% unladen/laden reflects the normal rider-to-machine weight ratio so that some asshat doesnt put in either a 2kg spring or a 2000kg spring....... wind it up to 30% laden ride height and end up with a poor suspension.

 

The exact ratio of laden-to-unladen ride-height is a personal matter and depends upon a number of factors uncluding use (tour vs track) and personal preference, but the fact is that the more compliant a suspension is, the better the contact patch stays in contact with the road. Hence the 15%/30% ball park ratio.

 

My point was.... for any given spring and any given weight on it, pushing it up from the bottom (preload) only lifts the top of it (ride height). It affects the spring's compressibility not at all. (until you reach the end of the suspension range and start to compress it....... but certainly you are smarter than that....

 

It's simple, and it's fact.

 

The rest of your argument is superfluous...

 

You have fallen into the classic trap of the word "preload".....

[dlaing]

The only thing that will affect the sag ratio for any ONE GIVEN WEIGHT is the spring rate.

 

Assuming Sag ratio means the ratio of laden to unladen sag, you are wrong.

If you start with say

15mm unladen

30mm laden

you have a 15:30 or a 1:2 ratio.

If you add 10mm more preload the sag will

decrease to something like

5mm unladen

20mm laden

which is a 5:2 ratio, not a 1:2 ratio and the spring rate has not changed as you said it would if the ratio changed.

The actual change varies due to progressive qualities of the shock or forks.

But there is no way the ratio is going remain the same when preload is applied.

 

Adjusting preload for ONE GIVEN WEIGHT will do nothing more than shift the ride height along the shock/fork length.

 

IF that were the only issue you could place the LADEN RIDE HEIGHT at 30% (or whatever) with any spring.

Yes, people do these things when they ideally should be buying springs.

 

 

The suggested 15%/30% unladen/laden reflects the normal rider-to-machine weight ratio

BINGO! As the rider to machine weight ratio changes, the ideal unladen/laden sags should change too.

To suggest it does not is ignorant and misleading, and that is what started this whole argument.

 

 

 

The exact ratio of laden-to-unladen ride-height is a personal matter and depends upon a number of factors uncluding use (tour vs track) and personal preference, but the fact is that the more compliant a suspension is, the better the contact patch stays in contact with the road. Hence the 15%/30% ball park ratio.

Compliance is the primary goal and we can better maximize compliance and do better than ball park if we use reason rather than the overly simplistic 15/30% ratio.

Still it is better than simply going with 30% laden sag and ignoring spring rate.

 

My point was.... for any given spring and any given weight on it, pushing it up from the bottom (preload) only lifts the top of it (ride height). It affects the spring's compressibility not at all. (until you reach the end of the suspension range and start to compress it....... but certainly you are smarter than that....

 

It's simple, and it's fact.

 

The rest of your argument is superfluous...

 

You have fallen into the classic trap of the word "preload".....

Preload may not have an effect on a linear springs compressibilty, but preload does have and effect on progressive spring's compressibility and on shock's compressibility.

It's simple, and it's a fact.

I have illustrated this effect, presumably because of the shock, with my measurements of adding preload and changing from a unladen ~21mm and ~50mm laden sag to an unladen ~6mm and ~31mm laden sag.

But it has little to do with what I am arguing about, as the difference is not that great.

 

 

I am arguing about two points:

 

One, that using the same ratio for both front and rear is bettered by following the advice of the experts and using different ratios front and rear.

 

And Two, what I have devoted 90% of this discussion to showing that

a lighter rider on a V11 may need less difference between unladen and laden sag and heavier riders more because of the ratio of the bike to rider weight. It is a small difference as I said, but none the less it modifies target sag, and I have clearly proven it to be true.

[g.forrest]

Now let me see if I've got this straight. <_>

 

REAL RIDERS have ABILITY and CONTROL! They don't NEED to understand anything about setting up suspension. They just ride it!

 

Forget all the adjustments and settings. They don't do anything anyway.

 

If a bike wallows, weaves, head-shakes, wobbles, washes out, bottoms, runs wide, or pogo's off the road out of holes, the rider is a spineless d!ckweed and doesn't know how to ride.

 

Anyone who wastes their time fiddling with numbers, swapping springs and spacers is an idiot.

 

A bike's handling capability is rightfully determined by the sloppiest suspension settings that ignorance and neglect can provide.

 

Dimwits who fiddle with their suspensions because they don't know how to ride are attempting to hide their inadequacy by trying to impress others with meaningless drivel.

 

Have I got it right now, Forrest?

 

well i'd say if the bike is wallowing shaking its head running wide and pogoing off bumps. it has a far greater problem than spring rate or sag adjustment. this would be the last thing to examine. far more important are compression and rebound. now you may believe you can help someone with a handling problem using the internet and 275k words. but in reality it can't be done. i'm sure like many others i regularly load up my bike with an extra 20/30 kilo of gear and head off on a trip, now most often i make no adjustment for this extra weight if anything possibly a few extra cliks on compression. now guess what, the bike handles fine. now all the finicky sag adjustments ''are out the window'' with the added weight! and also you may give your figures for your compression and rebound settings to another rider of same weight and same bike..will it be perfect for them. now do all your settings on your favourite piece of road with all it's imperfections at based on a speed of 60-70 mph now you think you have it perfect. now pass back along the same section at 80-100 mph. my point is simply! there is no perfect setting, unless maybe set for one section as on the track. and my point of just ride it! having ridden ridgid,plunger,girder,to fully adjustable, it does get back to riding it through or forever fiddling.

 

[Guzzirider]

I've worked out this formula to show the factors that affect the cornering of my bike:

 

A= The total mass of curries / fried breakfasts I have eaten in the last 24 hours

 

B= How many hours I have worked in the last 24 hours

 

C= How much sleep I have had in the last 24 hours

 

D= On a scale of 1 to 10, my general mental wellbeing (10 is the highest)

 

E= How many Guzzi riding hours I have put in in the last 24 hours (the more the better)

 

F= My general level of testosterone and bravado on a scale of 1 to 10

 

G= On a scale of 1 to 10, the quality of road surface and weather

 

H= The quality of gear I am wearing on a scale of 1 to 10 (full race leathers and Arai gets a 10!)

 

I= How many other riders I am riding with- each one equals 1 point

 

(A + B + I) - (C + D + E + F + G + H) = X factor. The lower the score the better my bike handles!

 

Tweaking suspension of course helps, but most of it is in my mind!

 

Guy

 

P.S. Please don't get too pedantic about the above formula- just making a point

[g.forrest]

guzzi rider..your formula makes the most sense of this whole thread.. i'd add one more..

 

A= IMPROVED HANDLING. A being alcahol