High Speed Wiggle

[bikebone]

OK! Here's one for you: I've got a 1983 standard GL1100. It is a very nice original bike that I have done lots of work on to keep it in tip top shape. When I pass a car at speeds between 65 & 90 on a road with a slight hump at the center stripe, the bike "shudders", so to speak just as I cross that line. It wiggles, as in "prelude to a tank slapper". Now, don't get me wrong, it's not the kind of thing that scares the sxxx out of me, but since none of my other bikes do this, I figure something is amiss. The steering head bearings are in great shape, properly tightened with no slop in the steering head. So, anybody got any ideas?

[gsanders99]

Not so much an idea, but a confirmation. I have a '83 GL1100i that tends to wiggle at speeds over 70mph. I have not experienced any other symptoms of loose or worn bearings in the axles or steering head. I have noticed it seems to be worse when my wife is on the back. Makes me wonder if, at least in my case, all those bags and stuff hanging on the tail end create some sort of drag that moves the front end back and forth a little.

Anyway, while it's not exactly what you are talking about, it is very similar: an instability that is exacerbated by speed and variations in road surface.

Maybe someone will post something more helpful here soon.

cheers!

[Sidcar]

Weight distribution could be your problem but what are your tyres like?
My Triumph Trident "white lines" something terrible when the rear tyre gets worn.
You could try adjusting your tyre pressures that might make a difference.
Also check your wheel and swinging arm bearings.

Sid

[bikebone]

I've ridden bikes with built in bags and a top case that would wiggle at high speeds; I soon realized that the more weight you have aft of the rear axle line causes this problem. This GL1100 is a standard model (no bags, no fairing, no trunk) So that's out the window. As for the tires, they are brand new Dunlop K491 Elites and I run the recommended pressures of 32psi. So, go figure. Maybe I need to just not worry about it.
Thanks for the input!

[WingAdmin]

My suspicion is that you are moving fast enough to unload the front suspension, enough that the tire doesn't have enough "bite" to keep it from wobbling. One of the main thing that keeps the front end from wobbling like a bad shopping cart wheel is the combination of weight and caster, invoked by trail. Unload the front end as you go over a large bump at high speed, and you've lost a lot of what was keeping that wheel in check.

[Dogsled]

The only time this occurs is, in your words 'on a road with a slight hump at the center stripe'.............................. so you're going over the painted road stripes?

You can believe this or not, if you're passing on a stripe, you are on that stripe longer than you imagine. Would you believe it may be a wobble if the road paint was wet and you did this. Well the reflective glass beads they add to the paint can give the same effect as wet paint if there is enough bead in the mix. For everything that has good benefits there can be drawbacks. This is another case of the DOT not giving a S**T about motorcycles.

If you feel speed can unload the front end suspension with extra weight in the luggage.....trailers would be out......

[bikebone]

I think the problem lies in my Wing. My other motorcycles don't wiggle when crossing the same lines at the same speed. I have experienced the slickness of the center stripe while taking a corner at speed and at a steep lean angle, but at those times the bikes don't wiggle, they just slide across the stripe. It's not too unnerving if you are expecting it. With my GL the wiggle happens when I'm pretty much straight up and just move across it. I still think it might be in the swing arm pivot. I can't feel any play when it's up on the center stand and I try to move the swing arm side to side, but I've checked most everything else. I'm going to pull the swing arm off next week and deal with the bearings & adjustment. Thanks for your input!

[redial]

Perhaps the GW has learnt to do that new dance called Twerking!

[dingdong]

How are your rear shocks? Weak rear shocks can cause this exact problem.

[Dogsled]

How are your rear shocks? Weak rear shocks can cause this exact problem.

When my air pump went on the blink I tore it and the 5 miles of wiring out. I plugged the air shock with a fill valve and added a few lbs to where it felt comfortable and I check it once a month.

'WEAK REAR SHOCKS, how would you tell if they're weak. The air shock seems to over ride the manual one sitting still and it feels firm. You state weak SHOCKS, plural, but you would only be talking about the coil spring one if the other is holding air.

What would be the test to see if the spring side is causing a problem? I wanted to change to a set of manual Progressive 412's but I hate to put that money into it and find out there is no difference..... I was try different air pressures and was amazed at how high the air shock goes up, I was on my toes at a stop sign. If it goes that high you would think even a new coil spring would be overstretched and less effective.

I just can't understand this air/spring set-up.

[dingdong]

Read both of these links. The air shock is there mainly to adjust ride height to accommodate for load changes. The spring over shock still handles the damping so if your spring over shock is bad you may get the symptoms you describe. How to test and descriptions of the differences between the two is described here.

http://www.wpsuspension.co.uk/setup.php

http://www.steelthundercc.com/shock_info.html

Edit: When testing the spring over shock let all the air out of the air shock.

[Dogsled]

Thanks DingDong,
Looks like i'll be doing my rears in the springtime for sure. They tested good in the driveway without air in the one one but without any air, the bike bottoms out on the road. I was using air to compensate that issue.

Thanks for thos links.