Shakin' All Over

[James Burleigh]

Not long ago as I was heading down the 5th Street exit off the Bay Bridge into San Francisco, on a straight section of the off-ramp I took my hands of the handlebars to fool with my gloves. Immediately the front end began to shimmy, and the bars started going back and forth (no tank slapping, but it probably woulda gotten there). I chalked that up to poor pavement, since they're doing work all around there.

Then this weekend as I was going across the Golden Gate Bridge after seeing the Queen Mary 2 come into SF Bay, I took my hands off the controls and started doing the Monkey Dance to try to close those %$#@*! zippers under the armpits of my Aerostitch 'cause I was starting to feel cold. Right away the handlebars started to shimmy and jump back and forth....

Now, I just got new tires put on, but the first shimmy was pre-new tires. So WTF? :blink:

Isn't a finely engineered piece of two-wheeled machinery supposed to be balance to the point where it'll go straight and true without my having to keep my hands on the bars? I sure don't notice any fighting during my usual riding. How in the hell am I supposed to stand on the seat while going across the Bay Bridge in the morning if this problem persists? :angry:

FJR MD's--What's your diagnosis please? (I know, I know... "Don't take your hands off the bars...." )

Jb

 

[unclekunkle]

Right away the handlebars started to shimmy and jump back and forth....
Now, I just got new tires put on, but the first shimmy was pre-new tires. So WTF? :blink:

Now I am confused ... when I read that it shimmyied again after a new fron tire was installed... cause thats typically the cause, when the front starts cuppin a little. If yer front tire is new and has a good balance, get some wrenches out and make shur everything is tight, right on down to the rear assembly as well as the front. Its not supposed to do that!

 

[madmike2]

1.) Its the nature of the beast...learn to live with it. :dribble:

2.) Steering head bearings loose.

I think I'd opt for #2. Have you had them checked? Also have them loosen and retorque the triple tree/fork tubes. Did you have them checked after your "fall down" so vividly captured on video?

 

[OrangevaleFJR]

Between different tires and tyres and with having things tightened down to correct torques I've noticed everything from perfectly smooth to slight wobbles at all speeds to more prounounced wobbles while slowing.

I attributed the varying nature of this to different tires and balancing and have noticed wobbles with both stock and Wilbers suspensions.

Perhaps a steering damper is in order? I don't know if that would fix it. Those with dampers speak up!

 

[markjenn]

We've discussed this quite a bit here.

You're probably doing right around 35-40 mph right? Maybe downhill a bit so it would stay at a steady speed without adding throttle? This is the worst case condition for this wobble because the front end of all motorcycles have a natural resonant frequency around 35 or 40 mph. Most bikes will wobble to some extent at one specfiic speed if you hold it there. We don't typically notice it that much because we don't ride without hands on the bars very much and when we take our right hand off, the bike immediately starts decelerating so it doesn't stay at the resonant speed very long.

All the following aggravate the wobble: worn/cupped front tire, wrong tire pressures, mis-balanced tire, defective tire, an out-of-true wheel, loose/worn steering head bearings, rear weight bias, worn wheel bearings, and maybe even the phases of the moon. Some bikes never seem to do it much, others tend to a lot, probably having to do with tolerances in frame alignment, wheels, etc.

It's one of those things where a little wobble is normal, and a lot is definitely not. If the thing immediately snaps into a quickly developing wobble anytime you take your hands off the bars around 40 mph, this is too much and I'd start working the list. The first thing to try if the front tire is worn is to get a new front skin, but it sounds like you've already done that (although I still wouldn't put it past that the new front tire has a defect). But after tire pressure, I'd probably take a good look at your steering head bearings.

Just by chance, how is the rear tire? If you replaced just the front, I'd wonder if perhaps the worn rear is aggravating the situation. I really try and replace in pairs, even if it means throwing away some front tread.

If keeping hands on the bars damps it out, it's not dangerous, just aggravating that you have to keep your hands on the bars. If you do it at 60 mph with the throttle locked, you'll probably find the front end steady as can be. If you get the wobble at a lot of speeds and ESPECIALLY at high speeds, then you've got a much more serious problem.

Good luck,

- Mark

 

[skyway]

You gotta love the british tax payers coin hard at work. :lol:

 

[Randy]

My dealer fixed this very easily. He said 'don't take your hands off the bars while you're riding'.

 

[HaulinAshe]

While you are greasing and servicing the steering head bearing, do a complete diasassembly of the front end. Check the bearing races carefully and look for damage or warping of the bearing seats. Think I read above where you had a drop and that could have damaged the bearings and/or seats.

But if you have not serviced the forks then do that while you have everything down. Dirty fork oil or even worse, imbalanced oil levels will induce wobble. Fork fluid has to be clean of foreign matter and EXACTLY matched from left side to right side.

Seen any leaks around the fork seals?

Checked your preload stripes L & R?

Checked your compression/rebound clickers (anybody been working on the front end)?

How many miles on the front wheel bearings (checked them lately)?

Jack it up and spin the front wheel slowly. Look for any sideways runout of the wheel. An easy way to do this is to tape or clamp something like a wooden dowel or pencil to one fork, so that it almost touches the side of the wheel rim. You can visibly watch the gap as you spin the front wheel.

Wobble is typically induced by a collection of small differences and tolerances that add up to just enough free movement and imbalance to induce wobble. There's some inevitably present. But brand new bikes don't wobble as much as older ones because most people don't take the time to keep the front-end tight and balanced.

 

[Fencer]

My dealer fixed this very easily. He said 'don't take your hands off the bars while you're riding'.

Ya beat me to it

 

[BentAero]

My ST1300 never had a head shake -until I replaced the front tire the 1st time. Every tire after that caused a head shake right about 45 mph w/ steady (locked) throttle. Some tire were worse than others, the Avon AV45 being the worst, Mich Pilot Roads being the least. My FJR doesn't do it ...yet, but I expect it will.

 

[evil_henchman]

100% tire related with mine. Pilot Sport on front = head shake.

 

[charismaticmegafauna]

Solving this will be one of the greatest contributions to motorcycling ever -- by this Forum.

Anecdote: once, while riding down a mountainside on the Pennsylvania Turnpike (not on FJR) I decided to lock the throttle, open my visor, open the tankbag, and change my sun glasses for clear glasses. Well, that took a little longer than I anticipated -- and about the time I was 'mid-glasses' (one pair in each hand), the h/bars started oscillating back-and-forth to extent that they went from front tire-squeal in one direction to front tire squeal in the other direction (probably leaving black stripes on the pavement?). I threw everything in the tankbag and forceably grabbed the bars -- almost broke my wrists.

Having 'outed' about my foolishness -- I think, more times than not, it's affected by changes in geometry from factory standard -- usually more weight biased rearward. That, and (as been mentioned, here) the subtle accumulated extra clearances all-over as well as a lessening of spring energy that happens over time. Maybe exacerbated by the addition on non-factory accessories (tourpaks, etc?)?

My advice would be to try more forward weight bias, as much as possible. Or, eliminating any rear-end-dragging (either by loading or design).

just my $.02, fwiw

 

[Scythian]

Wanna make it shake everytime?

Open up the throttle in a lower gear on a slight downhill and then just dump the throttle and take your hands off.

It starts shaking, but it doesn't progress beyond a head-shake.

The fact it doesn't progress to instability says to me that this is a known and controlled stability mode that exists due to some trade-offs in geometry/weight bias.

Imagine as a designer tweaking and modelling and testing everything until it is stable at high speed, under heavy front braking load, and resist 'tank-slap', but will headshake if deaccelerating under certain conditions without rider feedback on the bars?

I'd say: "Screw it! Looks good! Keep your hands on the bars!"

 

[twowheelnut]

markjenn's got it best. I'll simply say this: If you have a new/er tire in good condition, then check your steering head first and properly set your suspension. Keyword = Properly.

 

[Fairlaner]

If you were on the bridge could it have been those metal grates that caused your shake????

Richard

 

[cartfj40]

I'am reading with intrest this happened to me several time's at about 70 mph it shook so bad I almost coudn't stop it I only had 2.500 miles on it so tires shouldn't be the problem. I think it's sad for me I got this bike because I was sick of working on my 88 harley all the time and now I have my dream bike that needs ( head bearings torqed / new tire's etc. etc. ect. ) only 5.000 miles now so i will ride it for another season and work on the OLD JUNK HARLEY. I have to say this is not like any of the yamahas I have owned before they were very good in the fact I just rode them and not have to work on them with less than 10.000 miles on them. P. S. I love this bike but at this time I refuse to work on it. At 15.000 dollars with problems like this I think is SAD.

My .02

 

[temp357]

Did you get your wheels balanced?

 

[boogahboogah]

Had some head shake with the Metzeler Z4's after the first 5-6 thousand on the bike (OEM tires). Have not noticed the problem since switching over to the Avons Azarro's, but that might just be because I don't take both hands off the bars often...

 

[Fred H.]

Every single motorcycle I have ever ridden has exhibited this trait to one degree or another. Be it a Kawasaki, Honda, Yamaha, or Suzuki.

I believe it is caused by the natural "whirl mode" of a gryoscope as it spins down. Take any childs top and spin it on a table and watch what happens as it spins down and enters the whirl mode. Lockheed learned this lesson the hard way after crashing many Lockheed Electras when the props would literally rip the wings off the aircraft when they entered the whirl mode.

Many forces on the bike will act to dampen or reinforce the whirl mode as the wheel passes through a certain speed. Tires, and steering bearings will act to dampen it for the most part. Other forces on the bike (like steering geometry) can and will act to reinforce it. Tightening the stem bearings allows the bearings to exhibit more drag, hence they will dampen it some. Loose bearings will reduce any damping effect they may have, so it will be worse. An out of balance wheel or out of round or out of true wheel can also act to reinforce it. Cold tires do it worse than warm tires because the tires griping the pavement act as a damping force trying to resist the wobble, and warm tires exhibit more grip. Some tires offer more grip or have a center groove that wants to track straight ahead, so they may reduce it more than others. More weight on the front means the front tire is more planted, thus it tries to resist the wobble. Less weight on the front means it has less damping ability.

The only real solution to the problem that I know of is to add a steering damper to dampen out the oscillations. But that comes at a cost of responsiveness to counter steering input. There simply is no magic bullet. Keep your steering bearings tight, and good tires on the bike, and try not to take your hands off the bars around 40mph, especially with cold tires.

Tapered roller bearings in the steering stem will present more drag than ball bearings, and as such will act as a bit of a steering damper. Many have had good luck by changing out to roller bearings, and that will help reduce the wobble quite a bit. It is probably the single best thing you can do to solve it short of putting on a true steering damper.