"old" V11 sport frame

[dlaing]

This is the main reason you're measurement technique (though admirable) is not very useful.

 

But didn't his measurements verify what the sag numbers suggested, that he was not at 0.6kg/mm but close to 1kg/mm?

[dlaing]

I think I will retake the unladen / laden rear measure in case there is an offset between my measurement and the wifely one.

 

Hack, what is your opinion on the fork?

Good idea.

I measured incorrectly several times before Ratchet dropped by and helped me measure. (we used to be buds, way back...)

The best thing is to go by the pub and find a bloak your size and pay him with a pint to sit on your bike while you measure. just don't hand him the keys.

[dlaing]

Point well made, Paul. I would also submit that in terms of linear measure, rather than percent of available travel, the stroke of the shock is critical. Without knowing what application and therefore stroke the Ohlins manual is referring to, IMHO the Ohlins numbers Dave posted have little value in this discussion.

IMHO they have plenty of value.

OHLINS

Without rider: (A-

Rear: Road and Track 5-10 mm

Front: Road and Track 25-30 mm

With rider: (A-C)

Rear: Road and Track 30-40 mm

Front: Road and Track 35-48 mm

I did previously omit the travel.

The front is the same.

But the rear Ohlins has 10mm more travel than the Sachs and 6mm more than the specs for the White Power, presumably what Hubert has.

So, Hubert's shock is roughly ten percent shorter than the Ohlins, which puts him 3.5mm out of Ohlin's exceptable range.

Far better than Nogbad's rear Sag, but still an indicator that a stiffer rear spring would really help Hubert's bike....and it really is worth the money IMHO and even more so in Ratchet's opinion.

 

 

Hack, what is your opinion on the fork?

You didn't ask the rest of us, but in my less than humble opinion,

Without rider: (A-

Front: Road and Track 25-30 mm

With rider: (A-C)

Front: Road and Track 35-48 mm

and you are at 24 and 32mm.

Assuming your measurements are accurate, the fork spring is fine...but trim your spacer about 5mm.

Make sure your oil level is not too high.

Ratchet can give excellent advice on fork oil level.

[Guest Nogbad]

This explains why the front fork was jarringly harsh and chattered over undulations until I took almost all the compression damping off.

 

However, even if the springs are a bit strong by these measurements, I still find there is a fork dive problem on really hard braking unless there is some compression damping. I have not ever noticed that I have topped the forks out though.

 

It would appear therefore that euro-spec V11s had different rate fork springs than US spec ones.

 

I guess I should just throw away the Sachs.

 

In answer to Ratchet's question about the bump rubber, 11900 miles and a fair bit of 2 up riding, and the bump rubber is ok.

 

I might just take it to a specialist suspension shop and pay to have it sorted.

[dlaing]

 

I guess I should just throw away the Sachs.

 

It may make more sense than going through the trouble of replacing the spring only to find a blown seal or cracked eye further down the road.

[Guest ratchethack]

. . . I still find there is a fork dive problem on really hard braking unless there is some compression damping. I have not ever noticed that I have topped the forks out though.

This is unusual, IMHO, unless y'er air gap is far too large.... If this ain't the case, it's at odds with what I would expect.

You would not notice the forks topping-out. As I recall, they're limited by shock valving.

I guess I should just throw away the Sachs.

But you can't DO THAT, Herr Noggenwaffe! Y'see, in truth, I have actually taken a page (NOT A CHAPTER! ) from the ScroogeNog Playbook here. Y'see, having read enough scary stories about the impending early demise of my Sachs-Boge, I've been "Sweating My Assets" on this for far too long, expecting at least some potential for it to "let go" any time now. I have, however, taken some decidedly non-ScroogeNog precautions by routinely greasing the shock eyes and lubricating the scraper/seal. Unfortunately, I see only now that this has likely foiled any possibility of taking advantage of the ScroogeNog Early Retirement Plan for the Sachs-Boge. . . . .

 

The damned thing will not die. Now I have a great line-up on the spring I think would give me close to 20 mm laden/unladen sag difference, but it doesn't "pencil out" for me to install it on the Sachs-Boge and then have the shock fail!

 

So what I've been doing is set the laden sag to match the laden sag on the fork (38 mm yesterday), and crank up the compression and rebound damping to accomodate the resulting high rate and shortened effective stroke. While "tolerably functional" in terms of giving me correct chassis geometry, it ain't comfortable in the rough, near enough what I want overall, nor is it close to what I expect will finally complete the major dialing-in of critical components. So call me a hypocrite until the Sachs-Boge fails or until I install my next shock. Shouldn't be too long now. . . . .

[Guest Nogbad]

Hackette! Do you have the temerity to tell me now that after all your idealised ranting and raving and expert verbal diarrhoea over so many pages that YOU ARE STILL RUNNING THE MANKY OLD SACHS BOGE WITH ITS UNDERRATED SPRING!!!!!!!!!!!!!11

 

I'm SPEECHLESS with indignation!!

[Guest ratchethack]

Yes, I expected as much from y'er Noglitude. What else? Temerity is indeed one of my strong suits.

 

But at least I'm consistent with the open & honest, full disclosure thing. And being optimized to the full extent of the current gear and having done my homework on a however unintentionally delayed full plan completion seems to've set me apart a fair stretch here from those who've actually advocated the opposite (including y'er Noglitudeness), I b'lieve you must agree. . . .

 

The S-B may be a little manky, but at least it's working as well as ever at 30K miles. I'd never have expected it.

 

I may in fact break from the ScroogeNog instruction page after all and not wait for a full sweating of this particular asset. I have a record of ZERO downtime since I took delivery of the Guzzi, excepting only 2 days for transmission recall (my own removal & installation) that must be upheld, you see.

 

In any case I assure you that a complete and thorough update on suspension (to plan, of course) is not far away.

[dlaing]

Hackette! Do you have the temerity to tell me now that after all your idealised ranting and raving and expert verbal diarrhoea over so many pages that YOU ARE STILL RUNNING THE MANKY OLD SACHS BOGE WITH ITS UNDERRATED SPRING!!!!!!!!!!!!!11

 

I'm SPEECHLESS with indignation!!

 

...and a replacement spring is only $60 plus shipping.

...and if my wife would get a job, I'll buy Ohlins and sell my 475# HyperCoil/Sachs for $60.

Since Ratchet has sweetened to the point of a dry martini, I'll give him first dibs.

[Guest ratchethack]

A tempting offer, Dave, and thanks -- but I'm workin' a deal on a substantial step up from the S-B.

[BrianG]

I can't quite figure out the Italian philosophy of factory suspension parameters. I have heard the rationale for the Japanese parameters and they kind of make sense, but of course the MG parameters are pretty much the reverse of the Japanese.

 

Anyway, for those who might care, or even be vaguely interested..... The current theory about Japanese motorcycle suspension parameters for retail street bikes is thought to go like this. The front is generally set up for the Japanese concept of the "average Americal motorcycle purchaser"; to whit, a 170 lb (equiped) individual. The idea being that keeping the front forks "lightly" sprung makes for a more plush feeling, so you have a fork set at the soft end for a 170 lb rider.

 

At the other end of the bike, the legal beagles have suggested that the rear suspension had better provide all of the suspension required for 2-up riding, since everyone goes out sporting their sweeties or best buddies around, at least some of the time. Knowing that an undersprung rear end is frankly, dangerously unstable, the Japanese opt for a really firm rear suspension, for those few 2-up occasions, so that no-one ends up hurt from an unstable platform.

 

At the end of the day, the Japanese SOP give us an undersprung front end, and over-sprung rear end, for most north american-type riders. With this set-up you get a diving front end, on braking...... disconcerting but hardly dangerous. You also get a harsh back end....... hard to thrash fast, but certainly not unstable. All-in-all a stable, if unrewarding platform for the neophyte.

 

This whole soft rear spring of the MG is frankly surprizing to me. Perhaps the engineers of those days balanced increased compression damping with softer springs, but that's not the philosophy of today.

 

Todays' suspension philosophy, even on the track, is that a more compliant suspension better controls the activity of the contact patch on the asphalt. There's a lot of suspension motion available in modern suspension components, and the goal is to use it up. Adjusted for personal taste and total chassis stiffness, the spring design goal is generally stated: to provide 15-20% free sag, and 30-40% laden sag.

 

Once the chassis is properly sprung you can work out the damping, sorting out the rebound damping first..... trying to get one (and only one) full stroke cycle from most decent road bumps. Then add in a bit of compression damping to kill the second cycle, if you need to. Street bikes need precious little compression damping if they are properly sprung. You'll notice that the less sophisticated suspension systems provide adjustable rebound damping, if only one adjustment is provided.

 

Once the damping is dialed in you get to mess with the idea of "turn-in" if you are really into the twisties, particularly on the track. The balance here is that the boundary of rapid turn-in bounces off the consideration of head-shake on powering out of the corner. A steering damper can help a bit here, but if you see corner-exit headshake, you have over-pitched the steering head geometry by lowering the front or raising the rear, too much. A street bike should tend toward stability at speed, over scalpel-like corner entry, generally speaking.

 

Incidentally...... the most frequent cause of head shake in modern sport bikes is loose steering head bearings. Check them!!

 

Anyway... not to flog a dying horse........ but that's the way I understand the whole chassis tuning thing. This isn't complete, by any means, but it's a decent smattering of the current concepts.........

[Guest Nogbad]

Idea:

 

Given that you can increase the rate of a spring by shortening its working length, I am thinking of removing the action of one turn of the Sachs spring by making a nylon split ring that will go between the coils so artificially binding them. This will give a rate increase of 11% on a 10 turn spring.

[Guest ratchethack]

Sounds entirely plausible in theory, and in fact it might even be as easy as it sounds? But if so, why d'you s'pose it ain't already being done? I suspect that containing the forces under consideration in nylon - or much of anything else - may be easier said than done. Might be easier to just cut the spring, which many seem to've done with good results.

[Guest Nogbad]

Sounds entirely plausible in theory, and in fact it might even be as easy as it sounds? But if so, why d'you s'pose it ain't already being done? I suspect that containing the forces under consideration in nylon - or much of anything else - may be easier said than done. Might be easier to just cut the spring, which many seem to've done with good results.

 

Cutting is a solution to fork springs but not so easy with a shock spring. Dammit I might just get a Wilbers or something with a remote preload for 2 up riding.

[big J]

Fr chrissake just buy a decent shock,y' miserable sods