Author Topic: What might cause a low-speed front end wobble when coasting?  (Read 325 times)

Offline Mtbjay

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I've recently returned from a thousand mile tour of SO Oregon/NORCAL and discovered a new quirk in my bike.  Anytime I'd coast down from 35-50mph -hands-off the bars- the bike's front end would wobble back & forth slightly while decelerating.  Accelerating it goes away.  Hold the bars, it's barely noticeable.  I want my stability back!  What's going on?

I suspected it might be a loose head bearing, wheel bearing, or a weight bias issue.  However, I can't feel any looseness in the head bearing nor the front wheel bearing when I check it on the center-stand (by yanking it back & forth).  I may not be checking this correctly or thoroughly enough, but I'm confident enough that if any play exists, it's very minimal.

My suspension settings: I adjusted the forks & rear shock roughly 30% softer than what I normally run (for off-road comfort/traction). The settings were close enough to what I typically run that it seems illogical that it's the issue though, admittedly, I didn't firm things up while loaded to see if that helped. ::010::  I suppose running with less preload, the weight bias could have been shifted rearward just enough to allow the front end to wander.  Seems plausible, but unlikely, as I don't think I was far off from my usual settings.

I have no sag measurements to go by, just approximations.  Instead, I've used the stock recommendations as a baseline and altered the settings from there - always stiffer, with more preload and compression damping, minimizing fork dive.  I'm 180lbs, and my gear & boxes maybe 70-80lbs total, so stock suspension works for me.

Tires are my second set of Continental TK70's with approximately 2,500-3,000 miles on them.

What should I try next?  Things to examine?  My only thought is to increase the rear shock preload back to a firmer setting in an attempt to shift some weight forward, next time I'm loaded and touring...
2012 ST1200Z
OEM heated grips, bags, fog lights; V-Stream Windscreen, Fender Extender

Offline DarkLeftArm

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #1 on: June 10, 2018, 08:31:15 pm »
My money is on your steering neck bearings. Never had this happen to my Super T yet, but I have two other Yamaha bikes that have had it happen. A Road Star and a Royal Star. They both are notorious for loose steering neck bearings, and a lack of sufficient grease on said bearings. Both bikes just needed slight tightening, and the deceleration wobble vanished.
Cheers
Bert

Offline Ramseybella

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #2 on: June 10, 2018, 11:00:39 pm »
How's the front tire wear look, does it do a hump up and down dance at low speed coast hands off the bars?
My Triumph Tiger 1050 was the same way head bearing needed a tighten.
My mechanic argued i ask just check it and guess what? It went away.. 8)
"Technology applied for the sake of those who wish to escape it"

Offline Mtbjay

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #3 on: June 10, 2018, 11:33:22 pm »
Front tire looked good.  I’m looking for some good how to vids/pics on the head bearing adjustment. 
2012 ST1200Z
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Offline Boris

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #4 on: June 11, 2018, 02:55:34 am »
Go simple first, tyre pressures & weight bias. My guess is the latter.

Take any luggage off, add in some rear preload and see what happens.

Offline Mtbjay

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #5 on: June 11, 2018, 04:03:46 am »
For sure.  Looks like a bit of work to access the bearings: remove both calipers and pull the front wheel, pull the forks from the clamps, and pull the entire handlebar assembly just to isolate and access the head bearings.  The actual adjustment & repack looks like less work!
2012 ST1200Z
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Offline OX-34

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #6 on: June 11, 2018, 04:36:11 am »
.......... weight bias. ..........
Take any luggage off, add in some rear preload and see what happens.


I had a riding mate and his bike developed a wicked a head shake when he took his hands off the bars to coast or slowing down. We'd been doing some Iron Butt multiday rides so were fully loaded. After finishing the trip he took his bike (a Triumph Sprint) to the dealer and had the whole steering head bearing bits replaced. The bits 'didn't seem too bad' to the mechanic. Anyway, the problem had disappeared on his ride back home. 

Soon after we were back out on another IBA ride and the problem returned.  Back home he unloaded the bike and returned to the dealer a few days later to complain. But on the ride to the dealer he discovered the problem was gone.

The extra weight of touring panniers and fuel can etc was enough. Fiddling with rear suspension was all that was required.

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Offline Checkswrecks

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #7 on: June 11, 2018, 09:13:46 am »
+1 to the list others gave:
Steering head bearing tightness or wear
Tire wear
Tire pressure
Aft CG


A buddy crashed his Triumph 800 last month because of a sudden front end wobble while merging onto a highway. It went into a full tank slapper as he was accelerating and his last sight of the speedo was accelerating through 63 mph. The bike slammed him to the ground so hard he was kept in the hospital for two days due to a bleeding spleen. Fortunately, he was in full ATGATT with a Klim Latitude jacket, Motoport pants, and some model of Sidi adventure boots. His only other injuries were a broken thumb and lots of friction burns/rasperries through the jacket.


In discussing it, it looks like aft CG got him. The bike wasn't that old, steering head is tight, tires are in good shape, and he had checked tire pressures just that morning. However, he's a really big guy (both height and weight) who has to sit aft, had a heavy camping load mounted far aft, acceleration shifts the CG aft, and acceleration lightens the front suspension.
Damascus, MD
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Offline Ramseybella

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #8 on: June 11, 2018, 10:28:07 am »
Triumph put Shit ball bearings in the steering heads.
I had mine replaced good set of Roller bearings after the first time it acted up.
My friends 2002 Kawasaki Concours would do the same thing if overloaded.
Put the bike on the center stand and see how the head bearings feel.
From what i understand you don't have to pull the whole front end off to adjust them having the correct tools.
"Technology applied for the sake of those who wish to escape it"

Offline Sierra1

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #9 on: June 11, 2018, 02:23:25 pm »
Make sure the front tires aren't cupped from hard braking.  Use your had to feel for the cupping.  Sometimes you can't see the cupping.  Every bike that I've had has had the shakes as the tires wear/cup.
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Offline Squibb

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #10 on: June 12, 2018, 05:38:54 am »
My money is on two issues here. Cupped tyres, could be out of balance too, coupled to dry/seated steering head bearings.

The issue is probably there all the time, but only becomes uncomfortable when the CoG moves back with luggage/pillion.

Checking the tyre/balance is easy enough. The head bearings can be a PITA, but well worth the trouble, replacing/lubing as necessary. Make sure those bearing seats are good - failing seats usually shows as slight slackness in the immediate straight ahead, with some stiction becoming apparent as lock is applied. Trouble is we all ride around the issue day to day given it's slow progression, so we only really notice after a lay-off or maybe during a lengthy tour fully loaded.

Good luck sorting this out. Keep us posted.
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Offline Cycledude

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #11 on: June 12, 2018, 12:32:12 pm »
The wobble while decelerating with NO HANDS is very common on most motorcycles but most folks never notice it because they keep their hands on the handlebars, tightening the bearings will take away the wobble but tightening them to much will cause wondering issues that you definitely won’t like so be very careful .
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Offline Fennellg

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #12 on: June 12, 2018, 02:13:52 pm »
Just to be thorough check your wheel bearings.   I had my front wheel bearing fail on a Harley.  I was complaining about my steering and  braking.  They check it said it was fine.  20 miles later tank slapper lost the front bearing and destroyed my wheel.  Harley replaced under warranty.  Treat the symptoms with respect.  Could be nothing could be everything.  If something is different figure it out.  Something is not right.

 

Offline mebgardner

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Re: What might cause a low-speed front end wobble when coasting?
« Reply #13 on: June 12, 2018, 03:00:05 pm »
OP, you're getting lots of good tips here.

Mine is: This wobble has put you on notice. Checks has described a friend of his having a very dire ending, lets not that be you, right?

Please continue to look into this on your cycle, and I'm following to see what turns up, so please, post up what you discover :)
2016 ST, Non-ES, Power Commander PCFC, Seat Concepts, Rox 2" Risers w/ OEM lines, Aux: ADVMonster 44W LEDS and Dimmer, HL: NightEye H7 50W LEDs, Eastern Beaver CS3, Givi TN355 crash bars, Skene Designs Photon Blaster LEDs, Knight Design Wide Hunter lowering pegs, Denali SoundBlaster w/ Twisted Throttle horn mount, SW Motech Evo Side Racks, Saddleman X-Jumbo Cruiser Soft Bags, Hepco Becker Rear Rack, Hepco Becker Junior 45 Rear Top Case, MRA X-creen Tour, OEM reg. shield and bracket, OEM side wind deflectors, RideOn Tire additive, 0.55 in. LED eBay Voltmeter, Battery tender. Hit-Air Airbag Vest, Motoport 3/4 Length 3 Layer Jacket with Quad Armor Upgrade, EVS G6 Mesh Armor (summer), Revit 2 Layer Mesh Pants, A* Corozal Boots, Shoei Hornet X2, Garmin Zumo 550 GPS.

 

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