High Speed wobble

[Slow]

Hi all, I had the fright of my live yesterday.

It all happened at plus minus 90 mph, a sudden tail wag, wobble, that had me hanging on for dear live!

Here is some history;
I bought my R65 almost a year ago  with a RS fearing and panniers on.
The old lady needed a lot of work and I took my time getting her back to her former glory.
She looked stunning and I have since had two day trips of over 500 miles with her and she ran beatifully. The only thing that bothered was the heat, in sunny SA the summer tempreture gets up to 40 C on a good day, so I decided to fit an S fearing as she will do most of her trips in town as a daily runaround.

So, I took out my newly upgraded R65 S, just fitted S fearing, for a good fast run. Testing the limits and compairing it to how she was before.

She was running smoothly and I started to push her a bit harder. (I knew she was good for about 95 mph and I have reached 103 mph when she had the RS fearing on and she was stable at that speed.)

This is where it all when wrong, at around 90 mph.
I was very disappointed and thought she would run better with the lighter, smaller fearing.

What could have caused this live threatening behavior?
I went back to my workshop, still shaking, and started checking out all the possible courses.
Head bearing, tyre pressure, wheel bearings, all fine.
My conclusion, it must be lift, now how do I fix it or do I just live with it.


Out of all of this I have made the following assumptions;
1. RS fearing worked well, was very stable, but was very heavy and hot.
2. S fearing looks cool, the bike is light, maybe to light, and handles very well up to 85 mph.

Photos attached, RS & S.

[Barry]

I don't think some instability at that speed with a handle bar mounted fairing is any great surprise. Compared to the RS fairing the S is putting aerodynamic inputs directly into the steering. In the absence of a steering damper you could try increasing the pre-load on the head bearings or at least make sure there is some pre-load which is the desired condition.

[Burt]

It could be due to the shortened frame/wheel base on the R65, when compared to the /7, R100s, etc.  One of the reasons aftermarket seats are not available off the shelf compared to the larger capacity airheads.  

They are known to be unstable at the speeds you speak off especially when cranked over in a long sweeping corner and you hit a bump.  I have experienced it when fully loaded and it scared the crap out of me.  I thought I was history.  

They are not known as "Gummi Kuh" (Rubber cows) for nothing.  All I can suggest, is that you now know where the limit is!  

Now the RS fairing is something else and apart from its aesthetics, is probably one of the best designed full fairings ever made.  

Cheers, Burt.

[Barry]

Not only does the R65 have a short wheel base but the early 78 -80 model (Which is what we have here) is even shorter than the 81-84 model although only by a few mm.

[montmil]

My '81 R65 has an aftermarket cafe-ish fairing I bought new in the flea market at Barber Vintage Days for $40.00.

At a tested 100 MPH, it will give me a head shake saying, That's enough for now, hot shot. The first time it occurred was a bit unnerving. I just avoid that speed and all's good.

[marcmax]

My R65ls was cafe'd with clipons,etc. and I had no problems up to the ton. I added a Pirannah S style fairing. Fiberglass and about 3/4 the size of a BMW S fairing. Topping 85 mph it let me know it was time to back off the throttle.

Now as a sidecar tug, those speeds are just a memory.

[Tony Smith]

Hmmm.....RS fairing modified to properly fit an R65.

Just asking, but would you like to sell? I already own an RS and have evil thoughts aimed at getting a "mini-me" thing happening.

Also, this may sound dumb but was the problem you experienced a "wobble" or a "weave"?


comments from Muddly talker might help
https://www.youtube.com/watch?v=fvsDIq3WwVA

[Slow]

Thanks Tony, looking at the YouTube video, myne was surely a weave.
So I need to put on weight, fit new tyres or just go slower.

With regards to the RS fearing, make me an offer.

[NC Steve]

A timely question. I recently added a stock height seat to my '82 R65, after riding for about 1.5 years on a lowered saddle. I took a trip last weekend, and experienced the beginnings of a wobble at around 60mph, which got progressively worse as my speed increased. I did this a large number of times with the same result each time; below 60 I was fine. 

At one point, I was needing to ride on I40, and a driver came down a ramp to merge into traffic, apparently wanting to share the space I was already occupying. I needed to move to the left lane fairly quickly and pass several cars at 70mph to get back into my lane, and the wobble became so intense that I thought I was going to meet my maker. I managed to get past the cars and back into the right lane and slow a bit, but still felt as if I was going to lose control at any second. When I finally dropped below 60, everything smoothed out again. Needless to say, I had to change my drawers when I got home!

I run a small bar-mounted Givi fairing, and have not made any adjustments to it as yet, and around town it feels fine. The only other change was me changing all oil in the transmission, drive shaft and rear drive immediately before leaving on the trip, and have checked for any leaks. Tire pressure was fine, and the only recent change has been a return to the stock saddle. Would me riding appx. 2 inches higher on the seat have such a profound affect? It scared the "poop" out of me! I'm very hesitant to making even semi-high speed rides until I get this problem rectified, and in fact, had to pass on a BMW rally scheduled for this weekend in Boone, NC.  :-?

[Tony Smith]

Handlebar fairings have been the cause of many a wobble. There was a particular type fitted to CB750s by police forces all those years ago that were a pearler - they absolutely guaranteed that the copper would not under any circumstances exceed around 50mph - which made getting away from them on an old Velo a little easier than it should have been.


Point of this - take the fairing off and try again - no wobble you have your answer, if the bike still wobbles without the fairing, then you need to commence a careful and planned investigation.

[NC Steve]

Yeah Tony, that was my next step, to remove the fairing and see what happens. The shield had been working fine before, but I guess the geometry and drag changed when I put on a taller seat. I'm just really surprised that a seat might such a dramatic impact. I'm hoping maybe I could use the fairing again with some adjustments. Guess I'll see what happens, because I sure can't ride below 60 all the time, especially with the taller rear drive I've installed that gives the bike longer legs to stretch out and go...