uncomfortable wobble at 90 to 100

I have an slight but uncomfortable speed wobble/oscillation (not tank slapping yet) around 90 to 100 mph.

Ive already checked/installed

wheel bearings look and feel fine
13.5 progressive suspension shocks in the rear
tapered steering head bearings
tire pressure is correct
bronze swing arm bushings
telflex fork brace

N e ideas as to other simple stuff i can check?

I thought about doing a steering dampener.

thanks in advance

urbandork,

1. Cheap tires?
2. or so called non directional tires?
3. Fork lengths equal?
4. Fork oil?
5. Loose taper bearings?
6. Increase tire pressure to 30 +.
7. Front to back wheel alignment. (Use a laser level to check)
8. Weight distribution? (How much do you weigh.)
9. Loose spokes, especially in the rear.
10. Bent frame.
11. Handle bar rubber mounts. (dough nuts)
12. Front axle nut and axle holder (left side) tightened in wrong sequence.
13. Phase of the moon?
14. The gods of riding telling you you're going too fast!

1. Cheap tires? dunlop d404
2. or so called non directional tires? nope they are directional and on the right way
3. Fork lengths equal? yup
4. Fork oil? ... I think i should change it... what weight/type of oil do u recommend
5. Loose taper bearings? nope double check them and they are tight
6. Increase tire pressure to 30 +. yup already done so
7. Front to back wheel alignment. (Use a laser level to check) Will do ... n e advice as to which use of a laser lever works best? where to line what up with the laser
8. Weight distribution? (How much do you weigh.) ive been thinking about this too... im 145 and i have an xs750 tank which seats me about 3 to 5 inchs farther back then stock tank and seat... i know im lighter and since my weight is father back that stock i thought about dropping the triple trees a lil father down.
9. Loose spokes, especially in the rear. ... ill check
10. Bent frame. frame is fine
11. Handle bar rubber mounts. (dough nuts) i have clip ons
12. Front axle nut and axle holder (left side) tightened in wrong sequence.... ill redo to make sure
13. Phase of the moon? 66% full... uve got to be kidding me lol
14. The gods of riding telling you you're going too fast! probably... but i like doing the ton every now and then... and the safer the better lol

What year XS? the early ones had wobble designed in.
Hint; if it ever gets "worse" push on both handle bars. That will dampen the oscillation pulling on the bars will make it worse. I am no expert but I am not so sure lowering the front is a good idea that will steepen the rake which normally makes it handle "quicker" read less stable.

urbandork,


I haven't gone 100 MPH on either of my XS650's. The fastest I've gone is 85 on a moonless night when the gods of riding couldn't see me and I got away with it.

Traveling that fast puts you in the same class as professional racers. Professional racers have professional mechanics set up their bikes. I wouldn't recommend just guessing at these items.

#7.

1. With the bike held upright and a rider sitting on the seat
2. Hold the laser level on to one of the sides of the rear tire with the laser line aimed to the side of the front tire.
3. Mark the floor where the laser beam is.
4. Do the same with the other side.
5. Measure the distance from the marks to the side of the front tire.
6. The distance in #5 should be the same on both sides and parallel.
7. Adjust the chain adjustments to obtain the desired results.
8. The resulting chain adjustments should be within 1/8 inch of each other as measured from the pivot arm grease nipples to the center of the axle bolt.

As for the rest. Perhaps a professional will arrive here and help with those questions.

Re. spokes: check both radial and axial runout at rims. Yamaha's book spec is .080" (2 mm.); I don't like to see more than .020". When you reinstall tires, recheck balance. Re. steering dampers: those will help reduce head shake if you hit a dip or bump in the pavement when heeled over in a corner, but using them to mask suspension defects can cause grief. Re forks, my preference is Spectro fork oil. With unmodified OEM 35 mm. forks most folks use 10W. With cartridge emulators I use 15W. You might want to break down the forks and check the tubes for straightness, check for binds or slop in the sliders, check condition of fork springs, and check that the brace allows sliders to move freely. As gggGary has written, dropping the clamps will exaggerate the existing instability, and weight distribution isn't where your problem lies in any case.

Are your tires front and rear the same manufacturer and installed new at the same time? This is highly recommended

urbandork,

Here is a very complete book on motorcycle chassis tuning. In it, you can see what some of the considerations are for operating a motorcycle at race track speeds.

There are a number of little things, like, too tight steering bearings can actually increase instability and there is a lot written about the effects of weight distribution.

Small things, like control cables or even wires that are binding on the handle bars can contribute to instability.

http://books.google.com/books?id=l2...&resnum=7&ved=0CCAQ6AEwBg#v=onepage&q&f=false

If you are going to ride your XS650 at 100 MPH, you should read this book.

The technical detail in this book is very humbling and points out the fact that riding a motorcycle at high speed is best left to the professionals.

Urbandork,
A wise man would listen to Pete, everything he says I believe to be true. I however am not a wise man and will sooner or later test the upper limits of my bike. I for that reason bought a stearing dampener. The PO warned me not to ride this bike without one. He said all of his bikes have dampening of one form or another. Having said that all the other chassis tuning should more than likely be done as well. Good luck!

I wouldn't even attempt to go that fast without a good fork dampener........... I get laughed at for using the ole notched bearings as a dampener but I didn't fall off a turnip truck lately..........some front tires are also not as stable as others I have found.....like the cheapy Dunlops ...............

xsjohn

On page 27 of the above referenced book

5. Steering Damper

"Its only use is to stop steering flutter when the front wheel goes light over bumps at high speed or during acceleration. It will not cure weave or other stability problems and may make them worse..."

The author does say that a steering damper will be of some help for what he calls handle bar flutter or wobble at speeds of 35 to 40 MPH that occur with heavy acceleration or riding over bumps.

He refers to weave as occurring at speeds from 80 MPH to 120 MPH and that the steering damper will not help. Weave is specific speed related, and the ultimate cure is to have it occur at a speed higher than the maximum speed of the bike.

If you get yourself a 70 through 73 model you will cure your problem. They will scare you so much at that speed that you will never run that fast! I know. I have current 'sperience!!!

Lots of work to do. The bike was not really made to go that fast without some extra tuning and $$. Could be all or many of the things listed here. I always start with good tires in balance, good shocks, forks and a very good frame aligment both at the wheels and the front geometry. The XS was never intended to perfrom at those speeds in stock form. Even though they are built like tanks they are far from the techno they slowly phased in in future years.

urbandork said:

I have an slight but uncomfortable speed wobble/oscillation (not tank slapping yet) around 90 to 100 mph.

Ive already checked/installed

wheel bearings look and feel fine
13.5 progressive suspension shocks in the rear
tapered steering head bearings
tire pressure is correct
bronze swing arm bushings
telflex fork brace

N e ideas as to other simple stuff i can check?

I thought about doing a steering dampener.

thanks in advance

Click to expand...

Yep I know about the speed wobbles up around 90 when I bought my 1st 650 TX
It actually came with a factory steering dampener which in my opinion did SFA.
I just learnt not to sit around that speed and continued on enjoying my youth riding my bike everyday and in those days there wasn't much techno info around.
I think Yamaha skimped on the handling issues with the bike and I think that by the time the first Special was made they kind of sussed the problem and used tapered rollers in the headstem and I thought that the swingarm bushes were sorted but I can remember doing bronze S A bushes but it could have just been the early model.
The Tx650A was used by the police in some Aussie states but due to it's poor handling,and I believe that a couple of lives were lost because of this.....But I stand to be corrected.....It's only what I heard around the traps back then.
But when technology became more available and by taking note of 2 key issues (tapered rollers head stem and bronze swing arm bushes) I managed to beat the handling woes of what I think is the best bike ever to come out of the land of the Rising Sun.
Ride
Ride
Ride

If it's still a 650 I would be gratefull it still does 90-100mph

160kph is not out of reach at all for these bikes, even in stock trim. I occasionally find myself thinking "it's bloody windy today", looking down and going "oops!", and my compression is terrible currently. And it's completely stable too. But it's a 78, and they had solved all the big handling problems by then.

Correctly set up (35 mm. forks, tapered roller bearings in steering head, bronze bushings or needle bearings in swingarm, good shocks and fork springs, fork brace, quality tires, etc.), an undamaged '74 and later frame should be stable at 3-digit speeds without the addition of steering damper, frame bracing, etc. To add to the fine article Pete cited, adding resistance to steering head motion tends to slow any existing oscillation and widen its arc--not a desirable outcome. As the article indicates, the steering damper's function is to control "flutter" (AKA "head shake"), which isn't the same thing as oscillation.

Well, the book describes a situation where the author was involved in a 24 hour test and had to change the rear tire on a Honda 5 times in that period. The bike initially started to weave at 120 MPH, but as the rear tire wore, that speed dropped. So, we are not talking a lot of miles here on maybe a 2 mile race track.

That description has some value for ordinary mortals to understand their situation.

Lets say that you install brand new top of the line high speed tires on your XS650 and go out and blast down the road at 100 + MPH. Great. Now, you wait about 6 months before you try this trick again, but with the same tires that now have 6 months of wear. That means that you do not know at what speed the bike will start to weave. It could be at a speed less than your first run, perhaps at 95 MPH, but you will be complacent because you did it before and when it happens this time, chances are you will be surprised and not react quickly enough.

The point here is that all motorcycles weave or wobble. It's Inherent in the design. It's not a matter of saying "Well, my bike don't wobble..." All motorcycles wobble or weave. You just don't know at what speed they will start to weave.

The pros know all of this and they are prepared. They tune their bikes and tires to put the critical weave speed above the speed that they expect to go. They know that speed will drop during the race, and they change tires before it happens. Like, 5 rear tires in a 24 hour test period.

PS: Were we all surpsised that it was the rear tire?

Right, sustained 3-digit speeds on soft race compounds and track surfaces (highly abrasive) will shred rubber in a hurry. That having been said, in my experience there's nothing intrinsic to the later XS650 chassis that would cause oscillation below 118 mph (and maybe higher, but I haven't been faster on an XS twin, that's just where my motor hits redline as geared) as long as appropriate upgrades are in place and all chassis components, including tires, are in proper condition. An occasional high-speed run can be useful in providing early warning of defects--and right, Pete, Riding While Complacent is a ticket for a trip in the meat wagon, regardless of speed.

So Pete, what you're saying is... it's like a shopping cart where a caster wheel might wobble back and forth at a certain speed, but when you push it faster or slower it rolls straight... and all motorcycle have the wobble, but the engineers try work everything out to make the wobble only happen and speeds greater than the motorcycle will go?

What about those land speed motorcycles? Do they just get the wobbles out of the way at a lower speed before they're doing 300 mph, or do they fine tune them so well that they won't wobble until 400mph? I guess I'm trying to see if I fully comprehend the "all motorcycles wobble or weave" statement.