High-speed tail wag

[Guest Graham in NZ]

At speeds over about 180kph hitting a bump can set up a tail wag. I've increased the rear preload to give better static and laden sag figures and played with the compression and rebound damping at both ends but to no avail. My friend's 2002 model, with frame stiffening changes, is better but still wags a bit. It seems to me like frame or swinging arm flex rather than a suspension problem and looking at the swinging arm the eye which the drive shaft passes through looks like the weakness area to tackle. This eye seems to be much bigger than needed for shaft installation and movement. Has anyone reinforced this area, and if so what was the result?

[Steve G.]

I'm of the opinion that spine framed machines have an inherant weakness, and it is frame flex. I've resigned myself to that high speed instability that has been labelled "willowy" in many magazines. Stay away from the bumpy roads and it doesn't seem to be an issue.

Ciao, Steve G.

[Guest vkerrigan]

What are you running for a front tire pressure? Perhaps an increase there could help.........Good Luck..........vk

[Mike Stewart]

The looseness felt in the rear of the bike over slight road imperfections at high cornering speed (90 mph plus) is one thing I have been combating since day one on my 00 V11Sport. While changing the forks to Ohlins and replacing the rear with the Penske and playing with different tire brands, the bike to me still has a certain looseness trait. My bike is way better than stock but when pushed hard, I/it still feels somewhat nervous.

 

Now my 03 Rosso does not have this trait and feels like it is on rails. I don't know if it is just the wheel base difference or the extra bracing that was done on the frame.

 

Mike

[Baldini]

At speeds over about 180kph hitting a bump can set up a tail wag. I've increased the rear preload ... It seems to me like frame or swinging arm flex rather than a suspension problem

Had back end set front end going on my 02 in similar circumstance - hit a couple of bumps in a long uphill sweeper- found increase of rear preload helped but feel the behaviour is still there if pushed into it. I also wonder about frame stiffness on the spine even w/ the 02 onwards extra bracing. It appears to me that the area between the s/a plates & the spine should be triangulated, & the s/a itself just doesn't look up to the job.

 

I've commented on this before but most seemed to think as spine was developed on the racetrack we have nothing to worry about...well maybe if that racetrack had been the Isle of Man...

 

KB

[docc]

I'm afraid those who push these bikes hard on knarly pavement will always find their limits. Yet, there are so many things you can do to help.

 

The early red frames are the most susceptible ( shorter, steeper and less bracing).

 

The Pirelli Dragon Corsas original to my 2000 Sport were horrible weavers at speed. Every tire since has been better.

 

The steering damper might damp some of the low speed ( 40-45 mph) wobble but at the cost of heavy steering and INCREASED high speed weave. Most say least is best in the steering damping.

 

The high unsprung weight in the rear and generally high rear wieght bias are contributors to the weave. Increasing the front weight bias is helpful and there are several ways to do this as many have listed above. Moving your seating postion way forward ( 'climbing onto the tank', as they say) is a simple way to weight the front.

 

Echoing what Mike S and Lex have been telling us all along: get the proper springs for your weight. ( It's on my to-do list).

[gthyni]

I'll add my 2c now when I feel good about it.

 

I never experienced the tail wag last year with the

bike stock with Battlax BT57 sporttouring tyres.

 

After the winter projects this has changed:

- New fork, 30 mm shorter

- New tyres Pirelli Dragon Corsa with radical profile

- 120/60-17 front: 12 mm lower

- 160/60-17 rear: 6 mm lower

- new lower clip-ons

 

30+12-6=36 mm lowered front makes for a little steeper

and combined with the lower clipons and sport tyres it

should make the bike turn easier and it does.. it very responsive

 

The backside I could clearly feel the tail wag after bumps in high speed

(from 150+ km/h). Still I wasn't too concerned since the new fork wasn't

dialed in yet.

 

First steps:

- raise the tyre pressure to 2.4/2.6 bar

- dial in the new fork and stiffen the rear a bit to match

the Paioli (or an Öhlins ditto) can be run with stiffer settings

than the stock Marzocchi since it is more responsive.

 

Much better, but still noticable

both too hard and too soft suspension setting both make the

wagging much worse.

 

Still I wasn't happy,

but a got an idea - stiffness isn't always friend.

 

I had my steering damper (Öhlins) set to lower medium hardness

(like 6 clicks of 15) - I loosed it too just 2 clicks and went out for a ride.

The bike is just as stable as in stock config and much quicker through

twisties. I am very happy

 

The backside of this advise is:

I don't think the stock Bitubo steering damper is up to the task -

it just has too much inner resistance even a it's loosest setting.

So if you have trouble with tail wag - try removing the Bitubo all

together and take it for a spinn - if it helps the handling -

get a Öhlins unit.

[Lex]

Assuming you have at least gotten the basics (i.e. springs and pre-load) sorted you might find some help with damping (adjustments, re-valving or replacement) or you may have found the early spine frame's limit. I haven't experienced this (hard cornering at 90+ MPH on bumpy roads somehow fell off my do-to list ) so I can't really make a useful suggestion for a cure but I will throw our a pearl of wisdom I learned on the race track: If the back end misbehaves, work on the front and vice versa.

 

Whatever, I repeat my opinion that the V11 is a wonderful sporty bike and a great sport touring bike but both the engine and chassis are anachronism if you use it as a modern sport bike. Between the fixable poor stock suspension (rework or replacement) and the chassis's inherent flaws (I will not go into them here, they have been well covered in earlier posts) it seems like you are trying to make an apple into an orange. Don't let me stop anybody from trying, I could be wrong and it is interesting to watch, but I can't see anything making a spine frame into a CBR1000RR. Watching "the boys" in AMA formula extreme stand their bikes on the nose breaking from 199 MPH (~ 320 KPH) and slide their basically stock bikes into and out of a bumpy, 150 MPH (240 KPH) corner at Brainerd yesterday reminded me how far we've come.

 

I love my Goose and enjoy the hell out of it but I kind of like the fact that it has limits, how do you know you are going fast on the new supersports*? My best speed wouldn't even get the shock warm.

 

Lex

 

*Maybe seeing the fine the judge gives you?

[Baldini]

both the engine and chassis are anachronism if you use it as a modern sport bike... the chassis's inherent flaws (I will not go into them here, they have been well covered in earlier posts)

Lex,

 

I don't think it's a matter of getting the spine to behave like the latest jap stuff - I'd be happy if it matched my 25 year old Tonti...

 

Briefly...Suspension aside, What are the chassis' inherent flaws?

 

KB

[docc]

My chassis' biggest flaw continues to be the loose nut attached the clip-ons.

[Guest northend]

Funny, That's the same thing wrong with mine

[Lex]

Northend and Docc have it right, the big problem is with the operators, I'm just another example.

 

Seriously, the spine frame has some pretty basic problems. From front to back: the weight is biased toward the rear (and the very heavy engine can't be moved forward because of the location of the alternator), the rear suspension is very primitive; both bulky and the geometry seem to have a falling rate (the newer stuff isn't as progressive as it was when linkages first came out but it still "stiffens" as the shock is compressed), the swingarm is too short and the final drive is heavy, even by drive shaft standards. There have been allegation the fame and swing arm flex in the wrong directions but I can't confirm that. Through in mediocre quality suspension parts and poorly selected spring and damping and things can get interesting. In short, this is a fine 1980's chassis, it falls a bit short by modern standards.

 

Given that the Tonti has pretty much the same problems it is surprising to hear an unfavorable comparison. That would lead me to think you might find some improvement with suspension work. I'd start with springs (0.9 or 1.05 Kg/ cm in the front, maybe 500 In/Lb in the rear) and sort out the preload. That if fairly cheap ($200 - $250 USD) and easy.

[Guest 1100sport]

A little clarification might be useful here in order to avoid the inference that the tail wag problem is inherently associated to the spine frame. In fact it is not. As a matter of fact, the single quality that the 1100 sport and Daytona were most praised for was their incredible stability even at infamous speed. As already pointed out, this frame was originally designed for racing and eventually got pretty successful at it. So what went wrong with the V11 ? Well, at the time Moto Guzzi undertook to develop the V11, they lacked the required ressources to take on both the new gearbox development and a new spine frame to accomodate it. Basically what they ended up doing is simply bolt on the 6 speed gearbox to the former spine frame. Which is where the entire problem lies : with its much shorter dimension the new gearbox case is also much less rigid than the traditional 5 speed case, which eventually proved troublesome since the gearbox plays a crucial part in the rigidity of the spine frame architecture.

The Moto Guzzi engineers waited 2 years before aknowledging the problem and in 2002 released the v11 2.0. First they stiffened the assembly linking the side plates to compensate for the loss of rigidity of the new gear box. The problem is that they decided to go further. In order to gain stability, they also chose to increase the length of the spine frame. This was unfortunate for at least two reasons. First, as a matter of pure physics increasing the length reduces the rigidity of the frame. Second, this lengthened frame virtually realocates more weight on the rear, thus reducing the weight on the front. Eventually this modification has slightly altered the cornering ability of the V11 and, under very demanding circumstances, some drivers have also reported some rigidity problems.

One can only dream of the incredible bike Moto Guzzi would have created if they had the adequate ressources !

Mathieu

[Baldini]

...6 speed gearbox to the former spine frame. Which is where the entire problem lies ...less rigid than the traditional 5 speed case, which eventually proved troublesome since the gearbox plays a crucial part in the rigidity of the spine frame architecture.

... stiffened the assembly linking the side plates to compensate for the loss of rigidity of the new gear box... increase the length of the spine frame...reduces the rigidity of the frame...more weight on the rear, thus reducing the weight on the front.

Mathieu, That is a fascinating post. To me, it answers a lot of questions, makes a lot of sense. Thanks .

 

I've never ridden a Daytona or 1100 Sport, but recently, with all the comments from Paul & Zebulon re the Dynotec 1225 engine...5 speed isn't a bad thing...can it be got to change a bit quicker?

 

Lex, When I first got the Scura I posted here re handling problems & very much thanks to you & others I got stiffer springs & learned about how to sort the suspension. It now works well. I agree re s/a,drive & wt distribution but I think the Tonti engine/trans/cradle assy is inherently stronger than same on V11. Another problem, down to tank shape I think, is that you simply can't get enough bodyweight over the front on the V11 in corners. Love riding the thing tho, any chance I get just think it could be got better!

 

Cheers, KB

[Janusz]

So the best thing would be, as i see it, to have a 1999-2001 (old frame) bike and just stiffen the frame by linking the side plates.

 

Can that be done? My 2001 V11S is a fantastic bike without any problems from day one and only because of that I will keep it forever.