Bike started bobbling; gotta figure it out fast

[St. Arbucks]

Need some help diagnosing a problem with my bike. I was riding on the highway with some high wind gusts, and it was blowing the bike all around, which is not normal for the bike. I have 35K miles on it. Normally, it rides very planted to the road.

To describe it best, the bike bobbles with any lateral wind gust, or the slightest body steering (shifting the torso). It feels like a top that is wobbling.

Now, I know this is a hot button with us. I am not trying resurrect that discussion. My issue is that the bike is suddenly bobbling. By that, I mean that it very easily rocks back and forth on the back end, to the point where it (literally) scared the crap out of me when it started gyrating across the highway under a big gust.

I had just put a new tire on the rear, a PR2. While it is normal to get some feel of easy leaning with a new tire, this is more than normal. Further, the bike had been sitting on the center stand for 6 months while I was overseas. Not sure if that made a difference or not.

I pulled off the road for the night, and cranked up the rear shock adjustment (the knarled wheel on the left side). That seem to help. But I have not tired it on the highway.

I'm gonna start out in the morning and see if the shock adjustment helps settle down the back end. I'm not kidding, though, it was physiologically frightening. 'Nuff said.

Got any ideas what might be going on? I am in the middle of a trip and need to get this remedied.

Thanks,

Jim

 

[970mike]

Jim,

How is the air pressure in the tires? Did you get the right tire installed? I have just installed new PR2's front and rear on my ST 1300 and have no problems like that.

Best of luck. Please let us know what you find.

Mike

 

[KarmaDog]

Seems like it might be loaded heavy on the back end....it could be a tire problem....I doubt it is the shocks (other than it might not be set right to handle the weight you are carrying. Bottom line, I would ride it completely unloaded to see what happens first. These kinds of problems are frustrating, and usually something simple (just not simple to ID). Good Luck

 

[Rob Hephner]

It could be that you are simply not relaxed and getting into a feedback loop yourself.

 

[Rick77]

Seems like it might be loaded heavy on the back end....it could be a tire problem....I doubt it is the shocks (other than it might not be set right to handle the weight you are carrying. Bottom line, I would ride it completely unloaded to see what happens first. These kinds of problems are frustrating, and usually something simple (just not simple to ID). Good Luck

+1
I know when I added my top box, the handling changed on windy days. I'd follow KarmaDog's suggestion and unload the bike and see how it rides. A higher profile loaded bike will catch a lot more wind.

 

[nhdiesel]

Since it happened with tire change- I second checking air pressure, and correct tire...but also double check the axle torque. If its a tad loose, that wheel will start wobbling. If none of that takes care of it, start looking toward other things- like steering head bearings. My KLR steering head nut would back off from vibes (even after loctite), and would start with a tail wag situation.

Jim

 

[okckeith]

I know when I added my top box, the handling changed on windy days. I'd follow KarmaDog's suggestion and unload the bike and see how it rides. A higher profile loaded bike will catch a lot more wind.

I limit the weight in my top box. It sucks in the wind! Check your tire pressure. 42 psi

 

[St. Arbucks]

Thanks guys, I'll check these out. Much appreciated.

 

[Birdman]

Low tire pressure......

 

[Tom Mac 04a]

After all that was mentioned...
the only other thing I can think of is Loss of Pre-load on rear shock.. was mentioned it helped when the 'knob' was turned...
Maybe a re- oil fill procedure of the valve there would help if not enough preload left.

(low preload makes front feel light)

 

[Gunz]

Check the easy stuff first: air pressure, everything put back together correctly.

My experience with the PR2's (third set) is they are very touchy for the 500-600 miles. After they are well broken in, they are great until the last 500 miles, when they tend to get "greasy". I have found that on brand new PR2's, I get head shake above 120mph, though after well broken in, I can easily (and comfortably) run 130-140.

(In fairness, I mostly like the PR2's, though I only get about 5K from a set of tires, and I really hate the extended break in. But don't get me wrong, the PR2 is a good tire: good highway, good highway longevity, good rain, decent handling. However, as a result of my "antics", at 5K, they have no side grip left.)

Personally, I'd give your new back tire a few weeks to wear in, and then see if you have problems.

 

[Mellow]

After all that was mentioned...
the only other thing I can think of is Loss of Pre-load on rear shock.. was mentioned it helped when the 'knob' was turned...
Maybe a re- oil fill procedure of the valve there would help if not enough preload left.

(low preload makes front feel light)

I agree.. .at first I was thinking tires.. .might still be that... but your comments make the most sense to me.

 

[tdeboeser]

I had just put a new tire on the rear, a PR2. While it is normal to get some feel of easy leaning with a new tire, this is more than normal. Further, the bike had been sitting on the center stand for 6 months while I was overseas. Not sure if that made a difference or not.

My opinions:

I'm not sure, but if you've moved from a different brand of tire the profile maybe different and your suspension may need "tweaking". It's also possible because you changed only the rear tire the difference in wear could have thrown your bike off, possibly fixable by "tweaking" the suspension.

Among the other suggestions, try adjusting your suspension:


https://www.st-owners.com/forums/showthread.php?t=38515&highlight=rear+suspension

http://www.sportrider.com/tech/146_0308_set_your_static_sag/index.html



tom de

 

[wjbertrand]

Don't forget to dial in a bit more rebound damping to see if that helps. Also, double check they didn't install the tire backwards.

 

[okckeith]

double check they didn't install the tire backwards.

Good point I thought of that also!

 

[pepollock]

A key word is "suddenly". Worn shock and/or forks is a gradual change. Since the tire is new (a new tire would be a "sudden" change) that's the place to look first. Air pressure, rotation direction, seated correctly on the rim? With the bike on the centerstand, grab the wheel top and bottom and shake hard. Then front and back. Spin it. Then anything that gets loosened to do a tire change. Axle torque (I don't know the number off hand but it's basically really, really tight), pinch bolts, spacers in the right place? The top box is the next suspect. Next time it's windy, take it off and ride. After that, I'm stumped.

Good luck!
pete

 

[Strawman]

I'd take the top box off first. If you had the wind we just hd here in WI, It could very easily have moved you around. But after the weather warms up around here, I'll be taking the top box off. Until I need it for a trip etc. Handling is much improved with out it !! Next would be tire pressure. And shock settings. But don't just look at the rear tire. the front can cause much too. And weight distribution Too.

 

[Strawman]

Oh, Yeh. Don't forget driving in a real strong wind can cause you to grab the handle bars too tightly there fore you cause your own problem.

 

[St. Arbucks]

Today went a little better. Did a few hundred miles and managed to get over the Tappen Zee Bridge in one piece. (I was on my way to CT last night when all this started happening.) This morning, I stiffened up the rear shock a lot! It seemed to take about half of the bobble away, to the point where the bike was rideable. I also checked the tire pressure. It was 38 or so. I pumped it up to 42. I did the shake the wheel test--it was the first thing I did. Feels firm. I also retorqued the rear bolt, from UGGHH to ARRGHHUGGHH! (I don't travel with a torque wrench. )

As for the suddeness of it, I think what happened is that my rear shock was gradually getting softer, and then under the influence of gusting cross-winds, with a new tire that WANTS to lean over anyway, suddenly the shock was too soft for the new conditions (as one of the posters said above, about tweaking the suspension). I noticed that the worse feeling of no road traction was on concrete bridges where the grooves ran left to right instead of fore and aft.

When I get home, I need to take a careful look at that read shock. Make sure it's not low on oil or leaking visible. Not sure how one checks a shock, but I'll figure it out. (I always do. Mostly with the help of this website.

I will give the tire a few hundred miles to break in, as suggested. If it doesn't improve the rest of the way, off it comes. I just got a new Cycle Hill contraption and swapping tires is a breeze now.

Thanks one and all for your help and support. You guys are great.

 

[RealST]

Today went a little better. Did a few hundred miles and managed to get over the Tappen Zee Bridge in one piece. (I was on my way to CT last night when all this started happening.) This morning, I stiffened up the rear shock a lot! It seemed to take about half of the bobble away, to the point where the bike was rideable. I also checked the tire pressure. It was 38 or so. I pumped it up to 42. I did the shake the wheel test--it was the first thing I did. Feels firm. I also retorqued the rear bolt, from UGGHH to ARRGHHUGGHH! (I don't travel with a torque wrench. )

As for the suddeness of it, I think what happened is that my rear shock was gradually getting softer, and then under the influence of gusting cross-winds, with a new tire that WANTS to lean over anyway, suddenly the shock was too soft for the new conditions (as one of the posters said above, about tweaking the suspension). I noticed that the worse feeling of no road traction was on concrete bridges where the grooves ran left to right instead of fore and aft.

When I get home, I need to take a careful look at that read shock. Make sure it's not low on oil or leaking visible. Not sure how one checks a shock, but I'll figure it out. (I always do. Mostly with the help of this website.

I will give the tire a few hundred miles to break in, as suggested. If it doesn't improve the rest of the way, off it comes. I just got a new Cycle Hill contraption and swapping tires is a breeze now.

Thanks one and all for your help and support. You guys are great.

What are you doing in my back yard???

If ya need a place to bring it inside and mess around with it, let me know. Where ya heading too? And finally --- STAY OFF the Tappen Zee!!! Head north a bit to the Bear Mountain. Not only will you enjoy the ride up and down the mountain, its CHEAPER!