Twitchy bars w/ heavy load at low speed.

[xjwmx]

I had about a hundred pounds of luggage strapped on the back of my '81 today and the front end was very twitchy at low speed, like around 5 mph. Almost like wobble. At traffic speeds it was fine. I noticed this last time I had a passenger too, but never before then that I noticed. There's no issue unless there's a load back there. Any thoughts on a cause?

 

[5twins]

When you load down the rear, you lighten the front. Try dropping the tubes in the trees 1/4" or 3/8" to more firmly plant the front end or switch to slightly longer rear shocks (same effect). What you're trying to do is shift the weight bias more to the front. The Special models are probably more prone to this malady than the Standards because they sit lower in the rear from the factory. You're driving a "fashion victim", lol.

 

[gggGary]

A litely loaded front end will show up "issues " that are damped when more weight is holding it down. You might have an out of balance tire. Put the bike on the center stand jack the front or have buddy weight the back, turn the bars, are they "notchy" and want to settle back to pointing straight ahead? If so it's time for new steering bearings. Are the wheel bearings smooth, no slack, does the brake stick or rub? with the brake caliper loosened does the wheel stop at the same point or back spin to sit at the same point each time you spin it? If so your wheel is badly out of balance. Are your front and rear wheels tracking correctly? Bike on center stand grab rear wheel push side to side, any slop? Bad swing arm bearings can cause "wobble" a common comment is that the bike felt like it had a hinge in the middle.

 

[jayel]

A litely loaded front end will show up "issues " that are damped when more weight is holding it down. You might have an out of balance tire. Put the bike on the center stand jack the front or have buddy weight the back, turn the bars, are they "notchy" and want to settle back to pointing straight ahead? If so it's time for new steering bearings. Are the wheel bearings smooth, no slack, does the brake stick or rub? with the brake caliper loosened does the wheel stop at the same point or back spin to sit at the same point each time you spin it? If so your wheel is badly out of balance. Are your front and rear wheels tracking correctly? Bike on center stand grab rear wheel push side to side, any slop? Bad swing arm bearings can cause "wobble" a common comment is that the bike felt like it had a hinge in the middle.

exactly... good call gggGary, what's the condition of the rear swingarm bushings, front forks original ball bearings or tapered? swingarm and fork properly adjusted? need more info

 

[xjwmx]

turn the bars, are they "notchy" and want to settle back to pointing straight ahead?

Replaced bearings a year ago, but might have loosened up by now. They are balls, but were balls when it was okay too.

Are the wheel bearings smooth,

Fronts okay, rears okay and new

If so your wheel is badly out of balance.

Spitfires put on by pro mechanic in the spring have weights hammered onto them...

Are your front and rear wheels tracking correctly?

Yes, but just going by the marks stamped in the swing arm

Bike on center stand grab rear wheel push side to side, any slop? Bad swing arm bearings

Put in new bushings just after I got the bike. No movement.

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It felt a little bit like the forks flexing, maybe, instead of a "hinge in the middle"

Rear shocks are aftermarket, 13", old and possibly worn out. Springs seat was set at highest setting for the trip.

Thanks for the things to think about, guys. Maybe we can zero in on this. Meantime, put somebody on the back of your Special and see if you experience the same thing.

 

[gggGary]

To paraphrase Jayel " I actually reread the first post and now my comment makes absolutely no sense."

That twitch is pretty normal on any bike with too much weight too far aft. Once you know all the variables have been dealt with just take it as a warning that the bike doesn't like what you are doing and can bite. Our horses act the same way if there is something they don't like, they give off subtle warning signs. Ignore them at your own risk because they may make a much stronger point, usually at the worst possible time. Uh wives have a similar system.............

Good place to remind all that if the bike starts weaving or shaking, PUSH strongly on both handlebars to stop it, you CANNOT pull them hard enough to stop a weave. This has to do with the physics of your muscles and body not the bike. An early XS650 taught me this lesson and it was learn or crash at 80 plus MPH, whew!
Also front tires tend to wear the edges of the tread blocks unevenly and the worn blocks can start a weave or shake.

 

[xjwmx]

the bike doesn't like what you are doing and can bite.

It can also swipe at you with its paw; don't park it leaning too much with that kind of weight on it. It will rare up in the front and swipe at you from the side... I was having to find high spots to put the side stand on.

 

[XSLeo]

When you load the bike or have a passenger you need to add preload to the rear shocks and increase the rear tire pressure.
This will help on the twitchy feeling.
Leo

 

[xjwmx]

I wonder if setting the fork spring adjusters to the lightest setting would help. That should get the front down that much more without having any other effect, I think.

 

[XSLeo]

Setting the fork preload too light will let the forks bottom out more, not hold the tire on the road as well. The bike wouldn't carry a load as well.
No matter how low you want your ride hieght you need the suspension set up well or the bike won't handle well.
But then again those who do that care more about looks than performance.
Leo

 

[XSLeo]

Setting the fork preload too light will let the forks bottom out more, not hold the tire on the road as well. The bike wouldn't carry a load as well.
No matter how low you want your ride hieght you need the suspension set up well or the bike won't handle well.
But then again those who do that care more about looks than performance.
Leo