the speed wobble is back S4 baffled ???

[jerry]

The S4 up to 100mph the bike handles perfectly and suspension is spot on ,, speed wobble used to start at 125+ mph but now it begins at 100mph and gets worse until i back off

totally baffled checked all bearings ,tyres forks, frame and chassis alignment ,, all seems good , does it flat new smooth tarmac roads and bumpy ones no difference ,, front end suddenly goes light and the bars start wobbling add more speed and a tank slapper is on the card s, rear end is raised front is lowered ,,bike also ridden and checked by local ohlins suspension shop and al superbike racer they cant work out what my problem is either , they also say its spot on and a joy to thrash up to 100mph then it all goes to **** ??

ohlins shop fitted an expensive steering damper but it made zero difference so they took it off no point wasting £400 .

[Darkness]

Is it a sudden change Jerry, or has the speed at which it wobbles changed gradually?
Also, is there a trigger event, or does it slowly appear at constant speed and throttle?

[Darren69]

Something's amiss there but I'm not sure what to suggest. On the few very rare occasions when I have pushed mine beyond 130-135 on private roads, it has been far happier than I have. The chassis felt solid and engine still had more to give but I felt like I was being ripped from the bike too much for comfort.

I will pass on what my racing buddy once said; that problems felt at the front can most likely be attributed to issues with the rear. Make of that what you will. Certainly from my experience I have found this to some extent to be true.

[350TSS]

My S4 used to weave a bit above about 115/120 mph - I rarely noticed it in this country but then I did not often do that speed on UK roads. Crosswinds and continental tour bulky clothing seemed to influence whether or not it happened, it was much less likely in leahers
My first thought would be you are gripping the bars too tight. A motorcycle naturally has a track that shows that the front and rear wheels even when travelling straight cross each other regularly, try just resting your hands on the bars with your fingers extended over the levers so you cannot grip around the bars

[Darren69]

What he says, just go faster and ride through it! lol

[utopia]

This might be a red herring but, last year when I fitted my new ally swingarm and new wheels, I ended up having the rear wheel out on a frequent basis over a short period.
Somewhere along the line I must have mis-counted and I ended up with one chain adjuster a couple of flats away from its proper setting to align the wheels (which I had religiously checked initially, during the conversion).
Next time I rode it, there was a noticeable tendency to speed wobble above 100mph or so.
It wasn't massive at all, but the bike was definitely more skittish than it had been before.
On getting home, I checked the wheel alignment because it was the only thing that had recently been fiddled with.
It was out .. but only by one or two flats.
I corrected it and the bike was fine afterwards .. being put to the test in a few spirited rides in Italy the following week.
I could hardly believe that such a small error in wheel alignment would make a noticeable difference, but it seemed to.
This is on the 750 .. rear raised, front also raised but by less, so its a bit nose-down from std, flat bars, rearsets, with brand new bearings in both the new wheels and the swingarm .. though head races were originals and possibly due for replacement.

So, have you had the rear wheel out recently ?

[jerry]

I have tried a tight grip on the bars and a very loose grip ,, no difference
the wobble used to stat at 125+ but now is about 105mph its not sudden or caused by manouvre or bumps its a very sudden thing but garanteed to happen ,, tried riding through it but that almost becomes a tank slapper ,,very scary ..

Im going to recheck every thing again ,ideally i would tear the whole bike down for a full check and refurb as its cosmetic are tired , but its my main transport and I dont have a spare bike here as yet ,

meantime I have a loan of a really lovely Racing Green Benelli TNT 302 cc its actually brilliant 360 crank screams to 11,000 revs , lovely sound 6 gears load of power handles brilliant and looks good only 37bhp but it runs a good as my UK M750
twin front brembo 4 pot brakes , Italy design but chinese built its capable of 110 mph ,, can be bought new for and in Thailand can be bought new for £3050 its very well made ,, cant fault it much nicer than comparable Jap bikes ,, want to try the 500cc version as well ,, head light is simply awesome ..
Alex reckon i might even find a low mileage 2nd hand one for £2,000

we have been doing our own servicing on it and its well made and designed electrics and wiring and the motor ,, lots of Bias against chinese made bikes but this machine is superb the benelli design team in italy have some real talent

[jerry]

checked swing arm bearings and alignment again today and rear wheel bearings , as wheels were off had them both checked on a balancer machine at my tyre mans shop ,The PR3s look in great shape ,also checked head bearings again ,, nothing at all wrong anywhere ,,, bike out on a test ride this evening and its worse than ever ,, wobble starts at 70mph now ???????? front end feels horrible very nervous and light ???? but all settings are same as before ,,,totally confused
wonder if the puig handle bar fairing is a cause ,, but its been on the bike 3 years

Im not feeling a lot of love for the old girl ,, think she knows I want a new bike ha ha

[Mr Gazza]

Way back when I used to nearly always be in the saddle of a T140V, I found that they would all start a gently roll at 94mph. I could gun past that and all would be okay.
It turned out that it was down to the "Western" or US bars, You know the higher versions fitted to Bonnies?
If the lower, straight bars were fitted there was no problem at all. So I surmise that the wobble was all down to how the wind played on my upper torso and possibly a subtle shift of weight distribution.

This was of course a fixed and predicable phenomenon. Yours is a rapidly deteriorating thing.

Unless you are very rapidly putting on weight and width I would seriously have another very good look at the tyres, in particular the rear. You don't always notice how the profile is changing... Compare them to brand new ones.

I experienced some very weird handling when my old Stradas got down. I managed to change the feel dramatically by re shaping the rear with a surform (To the horror of some on here!!).
The amount I took off was tiny, but the effect was convincing. As it happened it didn't last very long either.

What mileage have your tyres done?

You also state that you had the wheel out and it was worse after... I have to ask if you checked the alignment when you put it back in?... And the pressures?

Hope you get to the bottom of it.

[jerry]

was going to try new tyres next Gazza, old PR4 ones havo done 8,000 miles they still have loads of tread left and the rear is not flat in middle ,, probably go for bridgstones

some people here are suggesting its weather related as we have low temps only 55f and a cold wind for thailand

but I say thats normal in UK ,,

[Mr Gazza]

.... Other straws you could clutch..
Could you have a leak of damping medium from the forks or rear shock?
Is it possible that someone could have been fiddling with any external damper settings?
Have you recently started wearing a different jacket on your rides? Or using a different back bag?
Are the fairing mounts secure and not on the move in some way... Have you changed the mirror(s)?

I know you didn't start riding motorbikes last week Jerry and I'm a baffled as you, but I'll bet it's the tyres.

[Mr Gazza]

Yeah. My Pirellis still looked good at 6000 miles but the shape had gone off enough to a make difference to the feel, I could barely detect the difference in profile.

The carcasses will probably be suffering a bit in the hotter climate, and possibly the compound too.
They do reckon the life of a tyre is 5 years whether it's worn or not... It might be less nearer the Equator?

8000 miles not at all bad though!

[Darren69]

I was gonna suggest wheel balance and tyre pressures but it sounds as if you have already checked that, so maybe as Gazza says it's tyres.

[spuggy]

also checked head bearings again

Stab in the dark, but here goes.

Have you actually looked at the head bearings, as in eyeballed them? Or just checked for play and moved the bars around?

My 900 passed those checks fine. But it sometimes felt a little odd at lower speeds - and was downright scary at speed with cross-winds.

Turned out the head bearings were assembled almost completely dry, likely at the factory. The bottom one looked like it had been in a canal for a decade (rusty, seized) and there was some distinct notching in the bearing race.

Night and day difference. In retrospect, it was obvious. But from the standard inspection, like the MOT guy does, you'd shrug, say "yeh, nothing wrong with that" and move on...

[jerry]

head bearings replaced 3 years ago with taper rollers absolutely packed with grease ,, just rechecked them again,

tyre are 3 years old , no suspension or damper leaks , everything else checks out although the rear rebound was set lower than i had recorded buti have set allmy suspensions settings to my best recorded values ,, i keep a spreadsheet

going to get some new tyres , problems is choice ,, pirelli diablo corse 3 available , as are maxxis , michelin PR3/4 again, maybe bridgestone battlaxe ???,,, we just dont get the selections available in UK and they are 30% more expensive too ...

had the pirellis twice before before, good but I could make them break away on bends to easy ,though all the track riders use them ,not sure about maxxis ,,,, battlaxe is what i want to try as they transformed my UK M750

Ho Hum

[jerry]

my tyre man says i am running my tyres at too low PSI ,,,

i use 30psi front cold and 35 psi rear cold ,, thay usually get 3 psi hotter when running he says I should put 32 front and 37 rear cold ???????

the Benelli i was recently riding had 36 front and 36 rear cold as reccomended in its manual ??


many thai big bike riders run 40 psi front and rear ????

in uk i alwys use 30 front 35 rear never had an problem

[emzedder]

Interesting thread, in my experience tyre profile, head bearing action (tightness) and simple things like bar end plugs/weights (which can make a massive difference) and jacket profile can cause head shake. But all the Ducatis not normally prone and stable as a rock.

[Luxexterior]

I think Mr Gazza is on to something with his tyre suggestion. I have had similar handling issues to the one you describe in the past when my tyres have been old or worn. When I say worn I don't mean worn to or beyond their legal limit rather tyres that, while looking perfectly, fine have been fitted for a while or covered a decent mileage. I assume that the profile of the tyres has changed with use or the compound has hardened in some way, either way new tyres have cured the problem.

By the way I have Bridgestones currently fitted to my 900ie & I can't fault them.

[emzedder]

Tyres wear unevenly due to camber on roads so can look to have lots of tread but actually no longer symmetrical in profile ... I'd agree.

[utopia]

You don't have any Slime type puncture sealant in there, do you ...?
I'm guessing not, but just checking.

[Mr Gazza]

I run 32psi front and 36psi rear. I check them nearly every ride out, after taking too long to realise I had a slow puncture in the rear one year.
I nearly fell off following emzedder through Lessingham one time when it was soft... Thought I had forgotten how to ride a motorbike!!

Taking the tyre profile thing to an extreme; I once had the brainwave of taking my Ajay for a quick solo spin on it's sidecar tyres, part way through converting it back to solo for the Summer.
It was an experience in hilarity, stupidity and fear. I managed to wobble about 70 yards up the road and promptly turned it round (Far from a feet up turn in the road!!) and paddled it back home. It was totally unrideable!

[jerry]

right .. some interesting progress today ,,

NOT the tyres,, my tyre man says they are still perfect profile and only 40% worn ,currently bridgestones are on back order , he has stock of pirellis and Michelins but a new set will cost £320 even with 20% discount !!!!!eeek !!!!! however he asked me how i set the Head bearings and I said to the torque spec in my S4 workshop manual 30nm ,,, ahha ,, '' not enough '' when we set up our ducati road bikes we set at 40nm and Thai roads always make head bearings loosen after a while even taper rollers ,, i had set them up a few days ago at 30nm ,, so we rest them to 40nm , felt the same until i went for a ride totally stable up to 115mph !!! no lightness on front end , bike also feels better in low speed corners and changes direction quicker than before ,,there is a slight wobble at 115mph but he reckons i should be able to dial that out with a few extra clicks more rebound on the forks and a tad more preload ,but he also said the wobble comes from road bumps , i acknowledge that but still the bike should hit 130mph with out and wobbles some more testing to come .

b


for now he said leave the rear end alone its seems fine he had a thrash on it as well and i was let loose on his 848 ,,

oh yes front tire now 32psi and rear 37 cold ,, when hot front is still only 32 and rear gets to 38

[utopia]

Funny that though ....
I can't really see how too low a torque/compression on the taper rollers can cause enough slack to compromise the assembly to such a noticeable extent.
I'm wondering if the bearings were properly seated when they were first fitted.
Maybe a slight burr was put on the housings when the old ones were drifted out, and this has caused them to not seat fully ?
I had the same on a front wheel that I overhauled recently .. new bearings fitted by a previous owner were shot in no time.

Just a thought.
Glad you seem to be on the right track though. (almost a pun there).

[Darren69]

It is interesting because Ducati still recommend ball bearings and not tapers and if you go to a dealer that is what they will fit, I thought that tapers would be better but maybe there is some method to the madness?

[Ron1000]

My evo head bearings went after 4500miles. I got them replaced with tapered race bearings.

Not had any issues with them.

[jerry]

well i fitted the tapers about 3 years ago with new bearing cups as the old balls were totally shagged
I only ever set them to ducati recommended torque but have had to tighten them up once before ,

I have also fitted them on my M750 and thats a perfect handler at top speed .

riding today when I hit 115mph the front end still begins to go light and as you go to 120mph it wobbles slightly ,, imperfections in the road little and big bumps seem to set it off ,I may have to try new suspensionn setting and see if it can be dialled out
,, the front wheel is obviously losing traction .. making it light feeling and then the wobble starts

[jerry]

CURED

yes problem is now solved rode the bike today in the rain up to 180kph (110mph) no wobble at all even took my hands off the bars ,, but could not power through to 220kph (135mph) due to lack of road space traffic and the horrible weather , but im confident that on a sunny dry day all will be well ,,



what did I do ,,,, well the head bearing issue was the main problem ,but the light front end and sensitivity to road imperfections has had me thinking about my forks suspension settings ,, and poor contact with the road at high speed ,maybe the damping rate was at fault ,reading all my manuals and setting advice manuals from the experts, made me think that low speed compression transition of my spring and oil damping was out of phase with the air gap high speed part of the equation , this gave me a plan , so i ended up putting the compression up from 4 clicks to 7/14 and dropped the rebound from 10 to 5/18 clicks and also cut preload sag from 25mm to 15mm, this fiddling took some testing and adjustments but its made a big difference ,, and looking at my old notes was a good setting 2 years ago , i think my more recent adjustments were made to compensate for the loosening head bearings issue ,, I will check them more regularly and use the tighter 40nm torque specs .

i am now sending emails to some techs I know in UK and USA about this tighter 40nm spec for taper roller head bearings see what they think



the rear end Ohlins PRCS 46 I have left alone it was not the issue ...its back to its best settings 6/10 preload. 12 /24 clicks compression and 18/40 rebound

[Jez900ie]

Good result!