high speed front end wobble?

[Guest]

I took my bike up to 200km/h (125 mph) today and at that speed I got a front end wobble. I have never had it over 180 before so this was new to me. I know I need to check the tightness of my steering stem bearings. But what else can help? Less or more air in the tires? More preload on the rear shocks? Seems like I need more weight on the front end. Less preload on front springs or damping adjustment?
Just put on new progressive rear shocks and rebuilt the front forks w/ 20w oil and progressive springs.
I also just mounted a front windscreen which I hear can cause handling problems, but there was no problem at 180.
Any other ideas?

[tkent02]

Swingarm bushings, wheel bearings, maybe a lot of little things combined.

[Crankthat]

Front tire cupping?

[hikermikem]

My front end wobble was essentially eliminated after I replaced my swing-arm bearings...

However, they were just a wee bit past their natural life:

http://www.thegsresources.com/_forum/showthread.php?t=197569

[bwringer]

The windscreen can definitely cause this all by itself.

Most common causes after that are worn tires, steering stem bearings, and swingarm bearings.

You mentioned a bunch of new parts, but also check to make sure your static sag is correct.

Also, 20W fork oil is too thick. Use 10W if you're a smaller humanoid, 15W if you're a galoot.

[John Kat]

I took my bike up to 200km/h (125 mph) today and at that speed I got a front end wobble. I have never had it over 180 before so this was new to me. I know I need to check the tightness of my steering stem bearings. But what else can help? Less or more air in the tires? More preload on the rear shocks? Seems like I need more weight on the front end. Less preload on front springs or damping adjustment?
Just put on new progressive rear shocks and rebuilt the front forks w/ 20w oil and progressive springs.
I also just mounted a front windscreen which I hear can cause handling problems, but there was no problem at 180.
Any other ideas?

I believe you've got most of the ingredients needed to induce high speed wobbles
The stiffness and the dampening effect of the front tire play a major role in the onset of a wobble.
In your case, the windscreen probably unloads the front end of the bike that in turn decreases the role of the front tire to calm any wobble.
Having put heavier oil weight in the front fork doesn't help eitheir if the tire can't stay in touch with the road at all times.
Last but not least, did you check the static sag of your suspension front and rear?
If your suspension is not set-up correctly it will run into it's bump stops and that will get a wobble started

[gearhead13]

Ok, I can turn my front damping down from 2 to 4. Maybe a notch less of front preload?
I put in new swingarm bearings when I put on the 1100 swinger a few years ago.
Front tire cupping? what is cupping? My front tire is older than the rear.
How much static sag is a good amount?

[John Kat]

Ohlins recommends the following:
Free Sag
rear: 5-15 mm
front: 20-30 mm
Ride height ( rider on board)
rear: 25-35 mm
front: 30-40 mm

[posplayr]

I think I would pull the fairing and retest and before doing anything else. There are several factors that can contribute and I would just want to make sure that it is not the wind shield contributing. Would want to eliminate that as a culprit if you plan on keeping it.

Then set the front end as recommended. After that it is an Easter egg hunt.

Look for a link Ohlins Preload that I started the Ohlins instructions are in there.

[dorkburger]

I heard wheel bearings mentioned. Mine would wobble at low speed with minimal pressure on the handlebars. New front wheel bearings cured it.

[gearhead13]

I think I would pull the fairing and retest and before doing anything else. There are several factors that can contribute and I would just want to make sure that it is not the wind shield contributing. Would want to eliminate that as a culprit if you plan on keeping it.

Then set the front end as recommended. After that it is an Easter egg hunt.

Look for a link Ohlins Preload that I started the Ohlins instructions are in there.

I bought the windscreen so I could go faster and not get my head ripped off, the wind blast at those speeds is tough.
Handling was totally fine at 180, but I have never pushed it further than that.
The idea was to try to bury the spedo on it (240km/h)(~150mph) Not much chances to go this fast at home, I am at my in-laws now and there is a nice stretch of highway here.