XJ High speed stability

[Warr]

As one gets up in speed on twisty stuff I've noticed.

The bike has a certain flex to it. Nothing uncontrollable
But just wondering if people could share experiences on where I should start
looking to reduce / eliminate it.
Be it wheel bearings or the swing arm??

My steering head bearings have been replaced in the last 12 months and that
made an amazing difference.

I posted this question up on the Yamaha XJ owners discussion Forum
Got one reply ... anyone else have any thoughts

The XJ frames are reasonably rigid. The flex is most likely from the forks
or swingarm.

You can really stiffen the bike. Assuming wheel bearings, tires and
suspension are in order...

- All bearings adjusted/preloaded correctly (steering stem and swingarm).

- Fork brace.

- Braced swingarm.

- Frame braces or anchor plate (anchor plate ties the top of the engine to
the spine of the frame under the tank).

Michael Oberle - XJ Nobody

[FROSTY:Me]

Sorry to tell ya this bud--XJ's flex --they aint like a modern bike
a definite part of the problem with your bike is the shocks. they make the flexing worse.
Next time ya feel her flexing try easing on a bit of back brake and keeping the throttle on.
The othe3r stuff-braced swingarm,extra plates up around the steering head
all help but its gonna cost a fair biit to get there.
Do all that work and you still have a $1500 bike when for example $1500 wouild buy you a 88 cbr600 on trade me.
Mines a 89 but basicly same bike as yours and on manfeild I was useing a shit load of body english and hangin onto the back brake to keep her in line.

[pritch]

It was always my understanding that the nickname applied to the XJ series was "The HInge". This from the feeling that there was a hinge in the middle.

[riffer]

Really? I thought that was the H1 - aka "the triple with the ripple"

[Pwalo]

Like Frosty and Pritch have said the XJ isn't a modern bike. Most Japanese bikes from the early eighties era were known to have slightly suspect handling and suspension. Lots of aftermarket frames available for bikes of this era.

You can upgrade your suspension, and improve the ride quality, but you're just going to have to put up with a bit of frame flex if you want to push things.

I have a sneaky suspicion that Yamaha didn't really see the XJ as a full on sportsbike.

[Paul in NZ]

Judged from where we stand now... All 80's bikes had handling issues. The bar has been raised somewhat!

However, most 80's bikes can be improved a lot by decent shocks (usually the main culprit) and a bit of tweaking all around.

Cheers

[Warr]

It was always my understanding that the nickname applied to the XJ series was "The Hinge". This from the feeling that there was a hinge in the middle.

Well I'll add it to my list of endearments for the beast!!
What about the FJ1200 then ~'88 ?

[skidz]

I always thought they made the bikes that way to test the riders skills out.

[Motu]

The pinacle of Yamaha handling was the XS1,and they never went beyond those heady heights.You don't know about ''the hinge'' until you've ridden the XS1.Wheel bearings,steering head,swingarm,shocks and tyres,get them all right and you got a nice handling bike...get one out of phase and you'll swing from one ''solution'' to the next,totaly lost on how to get it right.

[F5 Dave]

Damn, I get up too late & miss an opportunity to shitcane an old bike.

Took an XJ750 (not too far removed from the 900 of a friends) on a brass trip & grew mildly fond of it. I now recant that memory.

As I used to say with my GS11, nothing another 20 years of chassis development wouldn’t fix.

Some Progressive fork springs (fronts on Yams are generically too soft), some new oil. Some cheap aftermarket shocks, (Progressive/Ikon/Hagon etc). Check the bearing float in the swingarm. Run matched tyres in stk sizes. Oversize or worn rears cause problems.

Any more is total over capitalisation. FJs weren’t much better.

Motu, on a similar tangent I once test rode a TX500 (I think) with the rubber mounted handlebars & seemingly everything else. The TT500 I ended up with was a better roadbike. Even on the trials universals. & that was scary. A friend then bought an 8valve 500 which had a square tank but a totally different bike. Head didn’t crack while he owned it. Really.

The early TX goes down as easily the worst handling bike I’ve ridden.

Though the CX500 custom gets an dishonourable mention & the XZ400 was eating turkey with a wooden spoon award.

[Artifice]

funny thing. i think it was an old xj 900 or maybe an old rf900 in the video they showed us when i did my basic training course a few years back. at a constant 80miles or something the bike built up a weave and just moving your weight forward and pushing on the bars solved it. funny thing it was specific to that speed range, must have had to do with a built up harmonic frequency in the frame and wheelsize.
off the top of my head:
seems to be caused by a lot of things.
1) geometry (rake trail & wheelsize)
2) flex in the bike
3) loose headstock bearings and worn swing arm bearings
and is made worse by
4) worn tyres
5) wrong profile tryes.

the thing is, as it gets up on on side of the tyre. the wheel is starting to push back towards the centre. then it keeps going over onto the other sidewall and starts to push back the other way. a worn out tyre puts the pressure on the outside of the tyre sooner so make the problem build up a lot faster.

[F5 Dave]

Doubt it was an RF, that comes from another generation & mine is quite stable, even with a bunch of rear ride height added.

Otherwise prognosis is sound. However decent(ish) suspension helps quell the problem. Worn out saggy suspension makes it worse.

On the XJ I could let go of the bars slowing at 60kph & it would set off an oscillation that would look quite frightening but seemingly was ok to freak your mates out by sitting back & pointing at while entering town limits.

[Artifice]

mr friend mr-Google was helpfull in under standing (sort of) some of the issues.

"In general, the effects of structural flexibility on weave mode depend on the vehicle speed. At high speeds, lateral bending flexibility of the front fork and torsional flexibility of the rear swing arm more significantly affect weave mode, primarily because of the change of the external force due to yaw rate in lateral motion."
"a rider's vibration characteristics affect the motorcycle weave mode. Weave mode at high speed is stabilized when a rider's vibration characteristics are considered. The external force generated by a rider's upper body acceleration stabilizes rolling motion. Stabilization of rolling motion advances the phase of the front tire side force via the external force generated by rolling acceleration in the steering motion. This phase lead stabilizes lateral motion due to the external force generated by the yaw rate, which ,in turn, stabilizes the weave mode."
talks on and on this guy does

of course you could just put a sticker on your bike "Weavers R Us"

[F5 Dave]

Oh yeah forgot to mention the bikini fairings that were on early 80s bikes were responsible for initiating a lot of this malarkey as well.

[FROSTY:Me]

Ok I was trying to KISS it .
Yep the early XJ900 handle bar fairing was well known for causing a weave at high speed-180km/h+
Cured by an after market frame mounting kit.
In all xj900's 3psi too low in the front tyre and she will wobble into a full on tank slapper at high speed or funnily enough 60km/h
Ive already told warr about rear shocks and one day He'll pick up the progeressive springs I've got sitting here for him.
The old M48 michellen tyre on the rear used to cause a weave once it was 3/4 worn -dunno why.
Ive raced an XJ many moons ago and it wobbled -nothing ya could do about it-ya just accepted it and rode around it.
I actually won a race at Bay park against guys on faster bikes --because I'd hit the dip coming out of turn 1 and the damb thing would tank slap half way down the back straight. -theyd all back off -waiting for me to crash