Instability at high speeds

[wilsonsandy07]

Having some pretty squirrely/light shakiness at about 90 and above mph. Had one instance of tank slap that’s caused a deep dive into what’s going on. This has all been done after the tank slap happened. Single rider, 150lbs ish, 5’5

- brand new battlax bt46s / balance beads
- forks rebuilt/serviced
- front wheel bearings replaced
- air assist serviced and verified not leaking, set to 3 top and bottom
- rear wheel w/balance beads, centered on axle
-chain slack verified 20-30 mm
- tire pressure front 30 rear 35
- aftermarket rear shocks, 1 inch lower than stock no damping adjustement only preload set to 3 as well

plan on checking
- steering stem bearings/torque
- replacing rear wheel bearings/swingarm bearings


is there anything else I should take a look at? Maybe missing something?

[Rob S.]

Maybe you should have checked the swing arm bushings/bearings first. And not lowered the ride height. And I'd say you're about 10 lbs light in both tires, despite your light weight.
What model & year are we talking about?

[wilsonsandy07]

Crap I always forget to post year model 82 1100e

I only lowered the rear to accomodate for my height a bit, after having the bike for a bit I’m actually looking to put stock height suspension back on I just don’t want to put the stock ones I have as they are ancient.

Is it common to run 40+ psi?

[Rich82GS750TZ]

If you create a signature with your bike in it, you’ll never have to remember to include that info in your posts.

[Grimly]

Is it common to run 40+ psi?

No. Far more common is 32F and 36R.

[wilsonsandy07]

If you create a signature with your bike in it, you’ll never have to remember to include that info in your posts.

Very true need to do it lol

[wilsonsandy07]

No. Far more common is 32F and 36R.

I thought so, seen a lot of 32/36 but lots of different theories and preferences. Either way I don’t think I’m far off enough to have my instability caused by pressure

[bonanzadave]

Crap I always forget to post year model 82 1100e

Same,same,same. My solution is to just not go 100mph. I know.....IT SUX !!!

My list of replacements and checks is twice as long as yours.

My anomaly is more like a "weave" as if the bike is a hinge.

[alke46]

I used to have a similar wobble, but mine was as I was doing a right hand sweeper at speeds near 80 mph and up. Swing arm bearings had already been replaced, so the next thing was the steering head bearings. Now I only have memories of the front end wobble.
Good luck and let us know when you get it fixed and the wobble disappears.

[wilsonsandy07]

Same,same,same. My solution is to just not go 100mph. I know.....IT SUX !!!

My list of replacements and checks is twice as long as yours.

My anomaly is more like a "weave" as if the bike is a hinge.

I would say that’s a pretty accurate description of my issue as well, trying to really focus on what’s happening first when I feel it front or back. I’ll update after I replace swingarm and steering stem bearings hopefully that’ll do the trick!

[oldGSfan]

Not a fan of balance beads. Maybe others like them, maybe I didn't use the right amount, but they didn't work.

[Rob S.]

Same,same,same. My solution is to just not go 100mph. I know...IT SUX !!!

That's no solution. Are you trying to live forever?

My '73 Kaw Z1 had a high speed wobble. Killed the PO and tried to off me a few times. What I learned is braking, especially panicked braking, only makes it worse. So I would ride the footbrake, and gently apply throttle.

[rphillips]

Thanks for the input Tom. I've done lottts of reading and searching on the beads. Most everybody that said they didn't work "had not tried them", it was rare to find folks, that "had tried them" say they didn't work... I wish somebody could explain how they work for some & not for others. You'd think either they do or they don't. You'd think it would be very easy to prove scientifically yes they work or no they don't. It's been a debate for yrs but still nothing concrete that I can find.

[oldGSfan]

Thanks for the input Tom. I've done lottts of reading and searching on the beads. Most everybody that said they didn't work "had not tried them", it was rare to find folks, that "had tried them" say they didn't work... I wish somebody could explain how they work for some & not for others. You'd think either they do or they don't. You'd think it would be very easy to prove scientifically yes they work or no they don't. It's been a debate for yrs but still nothing concrete that I can find.

They were OK up to high speed, then on the dyno at above 100 the rear started jumping around like crazy and had to be cinched down super tight. I could see the dyno getting very jumpy on several of the runs. The shop owner said those are terrible for very high speed. This is not a scientific analysis by any means, and like I say, maybe I didn't use the correct amount (but I followed the directions). In everyday legal speed riding they were OK.

That could be why my bike only put down 182 HP - another guy who knows big HP bikes said 'there was more on the table'.

[bwringer]

I used to have a similar wobble, but mine was as I was doing a right hand sweeper at speeds near 80 mph and up. Swing arm bearings had already been replaced, so the next thing was the steering head bearings. Now I only have memories of the front end wobble.
Good luck and let us know when you get it fixed and the wobble disappears.

I suspect this is a good chunk of the answer.


Also, air pressure in the front suspension is a terrible, imprecise, leak-prone way to manage spring rate. Install a proper set of straight-rate front fork springs from Sonic springs or Racetech and set sag correctly. Lowering only in the rear can also cause instability.

The original 40+ year old shocks are junk. There are multiple threads here on choosing shocks, but Hagon or Progressive brand with proper spring rates make decent shocks for not too terribly much dough.

Until then, keep it under 90 I guess? Speed costs.