Setting Proper Sag

[Guest ratchethack]

Sorry to put you guys through this.

 

Cheers

 

Cat

No apologies necessary, Cat. It's only through struggle that persistent popular delusions and fantastic inventions of frivolous fancy get a proper stake through the heart.

 

Seems we all owe you a debt of gratitude for flushing out another Class Five Phantasm!

 

Ever notice how hard it is in the movies to kill a vampire?!

 

Ever notice that the more gruesome the ghoul, the harder he goes down?

 

My personal all-time favorite was Nosferatu.

But in the end, even he got his proper come-uppance (er, didn't he?)

 

Stick with the basics here, my friend. It ain't all that difficult -- but beware, lest thou be misled by those who wouldst darken counsel by words without knowledge!

 

-- and that most certainly may well include Y'ers Truly at any time, of course!

 

Watch this space and evaluate the dialog. Y'er bound to come up with something helpful here.

 

Learning actually has been known to happen here. Why, it's happened to me -- on a regular basis, at that!

[docc]

Whew! I'm dizzy.

 

Some of you know I just installed an Ohlins with #514 spring and TD fork springs 1.0 kg/mm.; I'm 185# in gear.

 

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

 

 

From the ratchet guidelines it appears the rear is too soft and the front too stiff. Yet, still within the +/- 5mm.

 

Also, I found the sag to increase on the front with a couple more gallons of fuel and I do have my forks raised 9mm as I like the weight shifted forward.

 

Just a case study, work in progress . . . + =

[Guest ratchethack]

+ =

Ah, yes -- a universal concept well rewarded by the efforts of the truth seeker!

. . .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), with forks raised (along with 10 mm raised ride height in my case, at the rear) to shift weight forward, and providing about a 24.5 degree rake vs. the stock "short frame" setup at 25 degrees. It's the best handling and best riding it's ever been. Like you, mine's also a work in progress, though all the basics and all but a few of the fine tuning parameters (high & low speed compression damping, for example) are pretty much nailed down on a more or less permanent basis.

 

I sure am pleased with the "short frame" geometry. Wouldn't change this one iota.

From the ratchet guidelines it appears the rear is too soft and the front too stiff. Yet, still within the +/- 5mm.

You've got it as close as I do. I figure if you're within the +/- 5 mm, most would be about as close as they're likely to care to get. Again -- there's no "perfection" to be had here!

[Skeeve]

FWIW, I'm definitely coming down on the side of "if the forks are too soft, increasing preload is only like putting a Band-Aid on a sucking chest wound: it may make it survivable short-term, but you won't like it."

 

The only solution to under-springing is heavier (correct) springs. Witnesseth the Honda GL1200 (& 1500) Gold Wings: Honda, in an effort to give a plush ride, SUBSTANTIALLY undersprung these behemoths. To compensate for excessive fork dive under (any) braking, they came up w/ the TRAC anti-dive system[1]. It's better than nothing or worse than nothing, depending upon road conditions. They maintained this system in the GL1500, albeit w/ slight changes. The solution(s)? Buying correct fork springs [Progressive Suspension did a heady business in these] or buying a new GL1800 [which development was undertaken by the engineer who had previously been in charge of sportbike design, who promptly threw out the old crap and put on a set of forks more closely sprung & damped to sportbike standards], & voila'! Better ride & handling...

 

Increasing preload on too light of a spring only leads to a harsh ride over small, sharp bumps that still bottoms over larger ones. I could do the math for you, but it's so simple that it's left as an exercise for the reader 'cause it just plain takes too long to spell out.

 

The "magic sag numbers" that Ratchet is trying to explain to everyone are just a shorthand "rule of thumb" method of determining which way you need to go w/ your spring rates: in and of themselves, they're insignificant, it is solely because of what they are indicating that makes them important. Fixating on the mystical qualities of sag numbers is kind of like buying motorcycles by which has the better numbers on their spec sheets: it's not which bike has the higher numbers, it's what the numbers are referring to that counts. Riding a 500# bike that makes 60 ft/lbs of peak torque at 3k rpm and 80 hp peak at 8000 rpm is much more enjoyable than riding a 400# one that makes 70 ftlbs peak at 10k rpm and 100 hp peak at 15k rpm, in any "real world" scenario. Yeah, bike #2 may circle a race track faster, but you're working a lot harder for those .2 secs/lap...

 

Can you have an acceptable ride w/o nailing Ratchet's magic numbers? Sure; everyone's 'acceptable' is unique to themselves. But if you get close to those numbers, from decades of racetrack experience on the part of people who are not Ratchethack, you'll generally be happier w/ your boingers.

 

'Nuff said.

 

Oh, btw: Damping adjustments? Only relevant once the spring rate is dialed in. Damping can only make the ride harsher w/o a spring in the mix somewhere.

 

[1] Which depends upon some linkages between the brake caliper and the internals. Several (all?) of the Big 4 were working on different systems simultaneously in the mid-80s that all had the same f/x: hydrolocking the forks in an effort to counteract fork dive. None of them are worth the added complexity & aggravation, & in fact, all adversely affect handling, if only to varying degrees. Honda's was one of the better approaches, & it still sux.

[Guest ratchethack]

+ =

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.

 

G (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.

[polebridge]

Does this help:

 

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

 

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

[Guest ratchethack]

FWIW, I'm definitely coming down on the side of "if the forks are too soft, increasing preload is only like putting a Band-Aid on a sucking chest wound: it may make it survivable short-term, but you won't like it."

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

 

Mind if I borrow that one, Skeeve?

 

Your post was well expressed, IMHO. I might emphasize that the general guidelines from which I derived the 18 mm +/- 5 mm are NOT really mine, as you point out. 'Nother words, I didn't just dream it up. I simply took universal concepts (that have been known to be true and well relied upon for all suspension systems) and applied them to the available suspension travel of the Guzzi.

 

If I'd had to come up with this on me own, it would've no doubt taken many years and many thousands of miles of really horrible handling. . .

[Dan M]

 

THERE IS NO "RIDER ONLY" SAG MEASUREMENT, AND NO "RIDER ONLY" SAG RULE!!!!

 

 

 

Maybe this can be done.

I'm picturing a rider in full gear, rear shock out of the bike grasped in two hands like a center about to snap a football, then whilst supporting the front of his body this way, balance each knee on a fork spring.

Get a close friend to make measurements.

[Guest ratchethack]

Maybe this can be done.

I'm picturing a rider in full gear, rear shock out of the bike grasped in two hands like a center about to snap a football, then whilst supporting the front of his body this way, balance each knee on a fork spring.

Get a close friend to make measurements.

As it happens, I remember Dave telling me this is exactly the way he measured the rate on his Sachs spring in his garage, but I think he said he was by himself at the time, and had to bend over with a ruler to get a read, while balancing on one foot on the spring. . .

 

D'you actually s'pose this is where the previously mentioned "rider only sag rule" came from?

 

D'you s'pose it's a good idea to make sure your medical insurance is paid up before attempting this?

 

Enquiring minds (well you know). . .

[docc]

. . . had to bend over with a ruler to get a read, while balancing on one foot on the spring. . .

 

 

I would consider bending over around you guys a dicey proposition.

 

One of the problems considering bike weight is the unsprung variable. While the V11 is arguably heavy for a sport bike, its heavy reardrive is unsprung. Running a stiffer rear spring for that weight may be misguided since all that weight is not acted on by the spring outside of rebound.

[dlaing]

THERE IS NO "RIDER ONLY" SAG MEASUREMENT, AND NO "RIDER ONLY" SAG RULE!!!!

Rider only sag is the difference between the sag without rider and with rider.

It is as simple as that.

Relying on a rider only sag of 18mm you are completely ignoring bike weight and compensating for it with pre-load.

This is a mistake. You should get the proper spring, and not compensate for the wrong spring with pre-load. Every expert agrees about this but you dare to disagree.

Using your strategy, if we take Sumo Sammy and Willie Shoemaker, Sumo Sammy will have no preload and a harsh spring and Willie Shoemaker will have too much preload and will bottom out frequently.

 

 

As it happens, I remember Dave telling me this is exactly the way he measured the rate on his Sachs spring in his garage, but I think he said he was by himself at the time, and had to bend over with a ruler to get a read, while balancing on one foot on the spring. . .

 

D'you actually s'pose this is where the previously mentioned "rider only sag rule" came from?

 

D'you s'pose it's a good idea to make sure your medical insurance is paid up before attempting this?

 

Enquiring minds (well you know). . .

Following my struggles of measuring without and assistant,

my fork measurement was done by you. (eternal gratitude )

The rear spring of my Penske's sag was measured by my wife, multiple ways and times to ensure accuracy....with a plastic caliper!!!!

[dlaing]

For simplicities sake magic numbers are a good idea, but it also good to know how to adjust the recommended numbers.

Regarding the front to back issue, I think it an appealing concept to make the front sag match the rear, but my experience and the experience of experts suggest that free sag should be greater in the front, and the difference between laden and unladen should be less in the front.

 

From

http://www.peterverdonedesigns.com/springs.htm

SAG -

Front -

Rider Sag - 30-35mm (25-30% of Full Travel)

Free Sag - 15-20mm (60-70% of Rider Sag)

Rear -

Rider Sag - 20-30mm (race), 30-35mm (street) (25-30% of Full Travel)

Free Sag - 5-10mm (extremely light bikes use less) (15-25% of Rider Sag)

 

 

http://www.propilotsuspension.com/setuptips.htm

Front

35-48mm laden

25-30mm unladen

Rear

30-40mm laden

5-10mm unladen

 

Traxxion

http://www.traxxion.com/technical.forkspr.install.shtml

Front

35mm laden

20mm unladen

Could not find rear recommendation except for Max mentioning 10mm unladen in the traxxion forum

 

Unfortunately Race Tech does not cover front free sag.

http://www.race-tech.com/SubMenu.asp?cMenu...1&showPage=

Bike Type		   Front %	  Front mm	 Rear %	 Rear mm	 Rear Free Sag mm
Street Bikes 	   28-33% 	30-35mm 	28-33% 	30-35mm 	0-5mm
Road Race Bikes 	23-27% 	25-30mm 	23-27% 	25-30mm 	0-5mm

[Guest ratchethack]

Rider only sag is the difference between the sag without rider and with rider.

It is as simple as that.

Again, "rider only sag" is a term and a concept not used or referred to in anything I've ever read. You've evidently dreamed it up. Can you cite any credible source that uses this term and the concept as you understand it?

 

I find this a particularly unfortunate use of terms. It's obviously resulted in confusion on your part, Dave, and I believe it needs to be flagged here, lest you confuse others, some of whom are no doubt trying hard to comprehend things that are confusing enough to start with! IMHO, the most misleading part of your use of this term is that there are NO proper sag calculations that consider just the rider! Again -- The only sag measurement that considers rider weight DOES NOT -- EVER -- CONSIDER IT "ALONE"! Laden sag incorporates the rider weight TOGETHER WITH the weight of the bike. Yes, this distinction is fundamentally important. There IS NO PLACE for the use of this term or concept in measuring sags!

 

Dave, I've used the simple guidelines I've suggested here to achieve what I consider to be solid success in setting up my Guzzi. It works very well in my judgment, and I'm fairly particular about suspension set-up. I've been very pleased with the handling and ride improvements I've achieved, which are a night and day improvement over the stock setup, IMHO. I've re-sprung front and rear and hit my objectives the first pass using the guidelines I've suggested here, and I won't have any need to change spring rates again. You're telling me that I've done this incorrectly.

 

Now at the same time, you've posted that you've completely changed out your entire forks (including springs -- without having even measured sags before doing so, as I recall) as well as your shock (and spring) once already, yet you're still bottoming-out in the rear, and have what by any road standards is a very stiffly sprung fork -- and yet you posted that now you intend to make it even stiffer by changing out fork springs again -- and also, you evidently want to change out your shock spring again . . . . . . By the numbers you've posted, neither your fork or your shock sags fit the guidelines I've suggested, and it looks to me from your numbers like you've got poorly matched and badly unbalanced spring rates front-to-rear. This may just be me, but I don't think I could tolerate riding a bike set up the way yours is for long, let alone enjoy riding it. . . Hmmmmmm. . .

 

I suggest to you Dave, that not both of our interpretations can be correct. May I remind you that one of us is all done here, while the other is evidently still off mucking about in the shrubbery both front and rear, and more'n likely still headed for the deep woods . . .

 

Relying on a rider only sag of 18mm you are completely ignoring bike weight and compensating for it with pre-load.

Completely false. [. . .sigh. . .] As stated so many times before, the difference between laden and unladen sags (BOTH OF WHICH are TOTALLY DEPENDENT on bike weight!) is UNAFFECTED by preload as long as a 2:1 laden-to-unladen sag ratio is maintained as I have posted in context for purposes of set-up.

 

I do not myself believe, nor have I ever suggested to anyone at any time that it is correct, or even possible, to compensate for bike weight with preload. In fact, not only have I never suggested anything of the kind, I've stated that preload is only properly used to maintain a roughly 2:1 laden-to-unladen sag ratio when spring rates are correct. Using this basic guideline ensures correct use of the entire suspension travel, as designed. I've also stated many many many many times that adjusting preload is no substitute for a correct spring rate! You will also note most recently (to borrow a metaphor from Skeeve), who illustrated this by suggesting that using preload adjustment to compensate for the wrong spring rate is like using a band-aid on a sucking chest wound!

 

I think you'll find that my general purpose guidelines as posted fit well within most (if not all) of the Pro suggested guidelines, including the ones at the links you've posted. 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.

 

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]

 

Gotta go now.

[docc]

Seems to me the only difference between 'laden and 'unladen' sag is the rider (well, and any other load). So the 'difference' or the 'guideline' and the 'rider sag' are all the same, no? Semantics perhaps.

 

Terminolgy can be an obstacle to communication but also an avenue to further one's understanding. To be sure what Ohlins calls 'ride height' is what we're calling the laden sag and our reference to ride height more pertains to the height of the front or rear above the tarmac which will affect the front-rear weight bias and center of gravity.

 

Also. it occurs to me that a spring must have some optimal preload. Traxxion Dynamics has something on this in their fork spring instructions. It seems like it ought to be a percentage of the available spring compression. I was able to get good sag measures by preloading my stock Marz spring an extra 9mm, but the fork topped out easily and limited rebound travel.

 

Finally, I'm thinking adding preload could affect spring rate only if the spring is progressive by pressing the spring into its higher rated region. Straight rate springs wouldn't change regardless of the preload.

[Guest ratchethack]

Seems to me the only difference between 'laden and 'unladen' sag is the rider (well, and any other load). So the 'difference' or the 'guideline' and the 'rider sag' are all the same, no? Semantics perhaps.

Here's why it's important not to get confused by a misuse of terms here, and why it's more than semantics.

 

We're dealing with two entirely different scales of measurement when setting up sags -- weight and linear measurement. In our case we use pounds and mm.

 

It's very easy to make the mistake of referring to one when one means the other when assigning sag values.

 

Laden sag is measured in mm. It is dependent upon both the weight of the rider and the bike.

 

Unladen sag, also measured in mm, is dependent upon only the weight of the bike.

 

The difference between them in mm is the guideline I've used and suggested. It is a LINEAR measurement -- NOT a weight measurement!

 

Now here's where it becomes very important to understand the distinction:

 

The linear measurement and weight measurement of the difference between laden and unladen sags ARE NOT SCALEABLE OR DIRECTLY RELATED TO EACH OTHER, because every rider's weight and spring rates are different. So an 18 mm sag difference in one case may represent 150 lbs., or it may represent 300 lbs. in the next case.

 

So using the suggested 18 mm +/- 5 mm difference in mm is NOT "rider only sag". Again, it may be correctly thought of as the difference between "bike only" and "bike and rider" -- but NEVER "rider only".

 

The reason that the 18 mm +/- 5 mm works for riders of all weights (and bikes of all weights), as well as for springs of all rates, is that it is a linear measurement related directly to the total available suspension travel -- INDEPENDENT of preload setting. For all practical, ease-of-use purposes, this takes away the confusing aspect of having to think about preload effects on rate as long as one maintains something close to a 2:1 laden to unladen sag measurement, easily and properly maintained with adjustment per the usual recommendations of the Pro's.

 

Therein lies it's elegant simplicity, and the reason that (as at least I found) it works so well and so easily for purposes of setup.

 

Sorry this is so hard to describe, but I hope this clarifies it??