Setting Proper Sag

[BrianG]

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.

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

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.

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.

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.

 

 

Hahaha.... that's too funny!

 

We've wasted all this time arguing the same side of the issue........... for the most part.

 

I have never heard or read of this theory of asymmetrical fore/aft springing but I suppose that it makes sense to the degree that the man/machine unit is unbalanced fore/aft.

 

The diversion into a discussion of progressive-rate springs and mechanical systems enters a realm of conjecture that is well past my experience and expertise. I think that the fact is that modern motorcycle suspensions are all rising-rate devices as a function of a number of design features, the sum of which pretty much defy my calculation capabilities.

[badmotogoozer]

guzzi rider..your formula makes the most sense of this whole thread

 

Or at least since post #2.

 

Rj

[Guest ratchethack]

I have never heard or read of this theory of asymmetrical fore/aft springing but I suppose that it makes sense to the degree that the man/machine unit is unbalanced fore/aft.

Nor have I. Except for specific kinds of racing and off-road, it doesn't make any sense to me wotsoever. For general purpose road riding (if you're not racing your Guzzi on a track, and it's licensed for the road, I reckon that's generally wot everyone here's doing), there's no support for the idea.

 

I just took a read of the best Pro sources I've found on suspension setup to see if I could find any stretch of interpretation that could be considered a guideline for asymmetrical fore/aft sags. Not one comment to be found anywhere. All the guidelines are for symmetrical fore/aft sags. By my own personal experience, when you get sags too far different front/rear, and particularly when the laden/unladen sags are too far out o' whack, which (as presented previously) being a dead giveaway for mismatched spring rates, this is a recipe for bad road manners at best, and a bucking bronco at worst.

 

Paul Thede, President of RaceTech, Inc., is pretty well known for his products (as recommended by many here -- I believe including yourself, Brian?) and for hosting Professional seminars on suspension setup across the USA. In Sport Rider Magazine, Issue : August 1995, Thede said:

 

"Using different sag front and rear will have huge effect on steering characteristics. More sag on the front or less sag on the rear will make the bike turn more slowly."

 

This is consistent with every credible source I've found. I don't think Paul's too likely to've changed his mind on this in the last 12 years, but of course,

 

TJM & in the case that you're racing something such as bar stools or ice boats, YMMV

[dlaing]

In Peter Verdone's site and the others that I have linked to, all of those ranges center around an indication of a firmer front with more unladen sag.

For example once again:

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)

from:

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

 

I have never seen a recommendation for identical numbers fore and aft, other than from you two, but certainly you would think the guy at RaceTech would know what he is talking about.

 

In addition, a Guzzi being a shaft drive bike MIGHT benefit from a firmer rear and more unladen sag than the numbers that I have seen seem to recommend.

Shafts work better with less joint angle and lowering ride height at the rear might help that.

Also with the bevel box being so heavy, heavier springing and damping than a chain driven bike might be of benefit.

 

How an expert recommends sag might be open to various interpretations:

If you bend Peter Verdone's numbers above in the direction of 18mm/36mm, you get kind of close:

Rider Sag - 30-35mm

Free Sag - 15mm

Rear -

Rider Sag 30mm

Free Sag 10mm

 

Also regarding unladen sag in the rear he says,

"(extremely light bikes use less)"

This is somewhat consistent with my point that more rider weight requires greater difference between unladen and laden.

A lighter bike is the same thing as a heavier rider proportionally speaking.

And less unladen sag results in a greater difference between unladen and laden.

But that is the only expert that I have heard allude to what makes sense to me, and I only today noticed that he wrote that, so it is easy to miss the fine details and what the implications

[Guest ratchethack]

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)

Hm. Let me speak to this by direct experience.

 

After I upgraded my fork springs (a tremendous improvement and great success in terms of hitting my target sags) , I put another ~10K miles on the stock Sachs shock with its inadequately rated stock spring before upgrading to my custom spec'd Wilbers 629 shock with 95 N/mm spring. Getting the rear re-sprung to closely match the fork sags for the first time made a tremendous improvement, and again allowed me to hit my target sags (again -- THE SAME, FRONT AND REAR) very close to "right on the money".

 

During the period of time after the fork spring upgrade and prior to the shock spring upgrade, I was obligated to crank in preload on the shock very close to the numbers that Verdone recommends above -- just to make the ride and handling "passable". I was NOT happy with this, exactly as expected, and fully expected it to be an intermediate, temporary step from the get-go. It was the equivalent of Skeeve's "sucking chest wound with a band-aid on it".

 

Once I got the Wilbers shock installed, I found that it fit my objectives as well established per the recommendations of every suspension Pro I'd studied for years (in the case of the Guzzi with 120 mm available travel front and rear, this translates to 18 mm +/- 5 mm sag difference -- FRONT AND REAR), and for the first time I got to experience wot I figure the Liugi's in Mandello had in mind for handling and ride comfort. Night and day improvement. With the spring rate to correctly match the load, I was able to set preload properly and achieve both laden and unladen sag targets while giving a full range of travel -- again, for the first time. This fits the kinds of experiences I've had with the greater number of the 12 bikes I've owned. (2 it doesn't fit had a rigid rear, 'cause they were "oldies").

 

Dave, since we have the same bike with the same frame geometry, and since you've already upgraded both front and rear springs once, and evidently seem prepared to do both ends over again , I would urge you to reconsider your apparent intent to go with stiffer fork springs along with stiffer rear spring when you do complete re-spring #2.

 

BAA, TJM, & I seriously doubt y'er M is gonna V.

[Guest slowpoke]

Let me see, do you guys work for a living?? Or do you...oh! that's right, you must work on computers. So, what's your boss doing right now? You guys have just too...much...time!! Just go friggin' riding!

[Guest ratchethack]

Hey Slowpoke -- It's Saturday evening where you live. Same here, since we're within wot -- 30 miles? I haven't got any idea wot my boss is doing right now and I don't give it much thought, even when I'm working, which I ain't now. He gives me lots of leash even when I am working -- probably an obscene amount far beyond reason (just the way I like it ), but fortunately, as long as I seem to be delivering to plan or above, he leaves me well alone just about all the time -- but I digress. . . Some of us like to fiddle with tech stuff on motorcycles. That's wot I happen to be doing right now. If you aren't interested, wot're you doing reading this on a Tech Forum on a Saturday night -- or are you working now , and is your boss directing you to read this and post an objection to it on a Saturday night??!!

 

Enquiring minds (well, I reckon you know. . .)

 

BTW -- got in two rides today -- one on each bike. Both the Guzzi and the thumper are extremely well tuned -- both chassis-wise, and motor-wise. And you?

[dlaing]

Let me see, do you guys work for a living?? Or do you...oh! that's right, you must work on computers. So, what's your boss doing right now? You guys have just too...much...time!! Just go friggin' riding!

How come we never see you out riding?

I'll bet you I probably have twice the miles on my V11 that you had on yours...but then again you probably put some miles on that Triumph, too.

Go buy a Guzzi, you Yamaha riding maniac!

Or at least make it to one of the group rides that Ratchet keeps missing or avoiding.

But at least he has some miles on his bike!

[dlaing]

Dave, since we have the same bike with the same frame geometry, and since you've already upgraded both front and rear springs once, and evidently seem prepared to do both ends over again , I would urge you to reconsider your apparent intent to go with stiffer fork springs along with stiffer rear spring when you do complete re-spring #2.

 

Right now I assume I have the allegedly 0.95kg/mm stock Ohlins springs that shipped with the Cafe Sport. Most would say this spring is too light for my 220 pounds plus gear and apparel rider weight. It feels nice and compliant, but I feel it could be better during braking. As I said before, it could just need a higher fork fluid level.

The preload on the front external adjuster is maxxed out, resulting in a 26mm/36mm.

I am about the same weight as BrianG, and I think he has a pair of 1.1kg traxxion springs in the front and apparently more difference in unladen and laden sags. I guess he must ride further foward, or maybe he switched to other springs. Maybe I just need to get my Corbin adjusted for a more forward riding position. It sure would help the weight distribution.

 

At the rear I have a 550 #/in spring, which after listening to the testimonials on this forum, I figured would be too firm, but after using it, I suspect it should be firmer.

The rear feels pretty good at 6mm/31mm, but as I said before, I think a progressive spring for my Penske, would better match the front end's progressiveness.

From this thread

http://www.v11lemans.com/forums/index.php?...0rate&st=60

about rising rate springs and other things.

HyperPro offers a spring with the following weight specs

Start rate = 90.13 Nt/mm. = 9.190556 Kg/mm = 515.0929 lbs/inch

End rate = 144.2 Nt/mm. = 14.70407 Kg/mm = 824.103 lbs/inch

But I am not sure where the transition points are. I don't want to give it too much preload and I don't want to be as firm as an empty freight truck on big bumps. I think the only thing I can do is try it.

 

A question for anyone, what are your sags and spring rates and how much do you weigh, and where do you sit?

[BrianG]

Right now I assume I have the allegedly 0.95kg/mm stock Ohlins springs that shipped with the Cafe Sport. Most would say this spring is too light for my 220 pounds plus gear and apparel rider weight. It feels nice and compliant, but I feel it could be better during braking. As I said before, it could just need a higher fork fluid level.

The preload on the front external adjuster is maxxed out, resulting in a 26mm/36mm.

I am about the same weight as BrianG, and I think he has a pair of 1.1kg traxxion springs in the front and apparently more difference in unladen and laden sags. I guess he must ride further foward, or maybe he switched to other springs. Maybe I just need to get my Corbin adjusted for a more forward riding position. It sure would help the weight distribution.

 

At the rear I have a 550 #/in spring, which after listening to the testimonials on this forum, I figured would be too firm, but after using it, I suspect it should be firmer.

The rear feels pretty good at 6mm/31mm, but as I said before, I think a progressive spring for my Penske, would better match the front end's progressiveness.

From this thread

http://www.v11lemans.com/forums/index.php?...0rate&st=60

about rising rate springs and other things.

HyperPro offers a spring with the following weight specs

Start rate = 90.13 Nt/mm. = 9.190556 Kg/mm = 515.0929 lbs/inch

End rate = 144.2 Nt/mm. = 14.70407 Kg/mm = 824.103 lbs/inch

But I am not sure where the transition points are. I don't want to give it too much preload and I don't want to be as firm as an empty freight truck on big bumps. I think the only thing I can do is try it.

 

A question for anyone, what are your sags and spring rates and how much do you weigh, and where do you sit?

 

You are right about our matching weights.... and I ride with a Corbin seat as well. although I find it sets me too far aft, as well....

 

Mine is the 2000 V-11 Sport, so I think it is the shorter/steeper steering head design compared to the CS?

 

In any case, you are right also about the 1.1kg spring-set in the Traxxion Dynamics modified (revalved) Marz forks. I find them a bit weak in hard braking, actually, and have been contemplating a progressive spring-set, but I have not figured out how to specify (and actually get) a spring-set that that is progressive from 1.1 kg onward. If you recall setting your fork-oil, you will recall setting it with forks fully extended. In order to get increased progressive springing from the air-space compression, I tried setting the fork oil height with the fork collapsed, and eventually got to 15mm of airspace remaining. That still proved unsatisfactory.

 

I also run A Penske shock with 500# spring, as set up by Mike Stewart.

 

This may well indicate what you suspected, about me riding with weight further forward than you do. I'm 6'1 and do like to snuggle up to the tank. I also have the clip-ons set to the most-open position.

 

I find this balances well and gets me the sag values I wanted........ although the numbers are not in easy reach, I'll try to find them in the manual in the garage for posting here. (I was shooting for 15/30%)

 

The forks are now adjustable for rebound only with minimal compression damping. I set the rebound so there is one jounce cycle to settle, unladen.

 

I run one click of compression damping at the Penske unless I have the 3-pce Givi luggage set loaded, in which case I run 2 clicks of compression damping. Again, I have the rebound set for 1 jounce cycle, unladen.

 

It runs nicely in hard twisties, but it's no 600RR. It does keep up nicely with the son's 'busa if the straights are real short...

 

At over 100 mph (indicated) it gets a very little bit head-shakey if the steering dampener is not dialed in 2 more clicks than I like in the city, but those 2 clicks let me ride all day at 100 - 120 mph.

 

This setup works great for my riding style and preferences, since I'm old and slow and like my plushness...

[dlaing]

Thanks for the feedback.

Judging by our spring rates, I should be closer to 15/30% than you, but my aftward sitting seems to throw it all off.

We have a lot in common with our setup.

Roughly same weight and height.

Corbin Saddle.

Penske shock (I customized it to have a 68mm stroke)

Mike Stewart's recommendation led me to order a 525# spring, but they sent a 550#spring, which I think turned out to be better for my aftward Corbin mandated seating. (I measured sag sitted about 2/3 of the way back in the saddle)

I did not go with the Traxxion fork upgrade but bought a Cafe Sport Ohlins forks from Mike Stewart who had bought them from Jaap, who had bought them from Antonio, who had bought them from some guy who converted his Cafe Sport into a side car hack. (Antonio, correct me if that story is wrong)

I am slow and like plushiness, too! (still working on the getting old thing at twice the drinking age )

[BrianG]

Thanks for the feedback.

 

(still working on the getting old thing at twice the drinking age )

 

No problem... issues shared are issues solved.

 

Just wait 'til you get to 3X the legal drinking age!

 

I have 2X on motorcycles....

[Bruce Reader]

Just to keep this topic going another 5 pages...

 

 

Given the availability of progressive springs-----

 

To those that may know the design principle involved in progressive rear linkages.

 

Is there room for such a linkage given the geometry etc of the standard swingarm and rear suspension attachment points ?

 

Does anyone have an idea of what this would cost to make ? say 100 units ?

 

Is this a stupid idea ?

 

Could it be anodised a gold like colour to match the Ohlins ?

[Guest ratchethack]

Bruce, IMHO this is NOT a stupid idea -- but for all practical purposes, it's probably one that will continue to remain just an idea. I was curious about this even before I bought my Guzzi. There have been custom one-off rising rate linked rear suspensions on V11's, but my inquiries on the availability of proven aftermarket versions at GuzziTech at the time came back with a negatory response.

 

Just eyeballing it, there would seem to be adequate room for one. On the other hand, since the short swingarm and ~40 lb. wheel/hub assembly present such horrific compromises to the rear suspension to begin with, the return on effort, considering requisite R&D and production tooling on such a thing, would seem to be pretty limited -- not to mention the ultra-tiny potential market demand.

[dlaing]

I agree with Ratchet!

It is a fine idea, but I would be amazed if you could sell 100 units.

Maybe if they were under $100??????