high speed weave

McDonalds has the answer to high speed weave. Eat more.

http://www.youtube.com/watch?v=z3OQTU-kE2s

So that's why I've never experienced a high speed weave.

Great bit of video, did not know that laying on the tank could stop the wobble so easily. I have never had the problem at any speed, probably due to weight.
Seems like most every bike made back then was capable of high speed wobbles when ridden by a lighter rider. I suppose not much has changed other than the average weight of the riders and the use of the hydraulic steering damper.

Glen

Interesting video but I have to say that I never experienced what they show on a Norton or on a 750 Honda of that vintage and, at the time, my "fighting weight" was 137 lbs and I was routinely over the ton...

However we know that many people have experienced wobble and tankslappers. Perhaps it requires a certain confluence of events, a certain weight, certain type of road and speed.
It does not appear that they are inducing the wobble via the riders effort.
To be on the safe side, I will continue my double-bacon-cheesburger eating ways.

Glen

I used to know Dave Rawlins back then....He was a test rider for Norton before moving to Dunlop as a tyre tester when Norton closed.....didn't see him weaving and wobbling quite like that, but I did see him ride through a 200 yard marker board, at Gaydon, an old airfield used for racing in the '70s....lucky for him it was made of light plywood....

VERY interesting video

in all cases, the lighter the rider the more likely the bike will weave

in addition, it is clear that moving the rearward reduces the weave, exactly my Commando experience

I have been in a severe high speed wobble twice. Before the middle age bulge came along.

Once was mid 70's on an RD350 on an Iowa gravel road at 80mph. I crashed and didn't even remember what happened. My buddy had to fill me in. Nothing broken but I got a bit of road rash. Glad I was wearing a leather jacket, gloves and a helmet.

The second time was 10 years later on a RZ 350 racebike. I was doing some plug chops on a deserted highway. After reaching 100 or so I sat up and it shook so hard it ripped the bars out of my hands. As I was sliding off the back of the bike I got my arms around the back of the tank and the bike straightened up and continued on down the road as I pulled myself back up to the bars. I never tried setting up again at speed. Jim

I'm convinced that the reason it goes away when you lie down is because the weave is exacerbated by the rider's shoulders and arms going into an oscillation. It might even go away of you let go of the bars, but it's a brave man that will try that.

That is one wild speed weave. :shock: I have never experienced that intensity on any of my Norton’s. I get a tinge of it if my rear tire was low on air and that would set up a tail wag on the sweepers. My weight coming out of high school was about 165 lbs in the 80's. I am running about 175 now. Maybe I'm Fat.
Thomas
CNN

pommie john said:

I'm convinced that the reason it goes away when you lie down is because the weave is exacerbated by the rider's shoulders and arms going into an oscillation. It might even go away of you let go of the bars, but it's a brave man that will try that.

Click to expand...

You may be right. I know the sweepers sure get a lot smoother if you relax one arm and only push with the other arm to countersteer. Jim

I've seen it mentioned that aerodynamics is suspected as being the cause.
Getting down on the tank, or changing arms or even legs positions alters the airflow...

Some pleece bikes were forbidden to have high speed pursuits, since all that radio and panniers and screens haven't been tested in a windtunnel for stability.

Good video, as being 15 stone, it seems my only worry is BURSTING the tyres? BTW there is definitely no chance of being Aerodynamic!

They found the old ' center rain groove ' didnt help things , so they said somewhere . :? & I( thought it was just kawasakis that did that .

Moving weight rewarded makes matters much worse!!!
The air flow over the rider sitting up right pull them back an take weight off the front wheel.
Laying on the tank improves air flow and at the same time puts weight of riders head an upper body closer to the front wheel so loading the wheel.
All modern machines have more weight at the front. Sports bike designers go to great lengths to load the front wheel Honda fitted two radiators to their VTR v twins so they could move engine 30mm front. Benelli put the radiator under the set on the Tornado for the same reason.
also the comment about each fork leg moving independent of the other is due to weaker thinner old style forks. Fitting a for brace will help beef them up. Look at the size of any modern sports bike fork leg and wheel spindle they make Commando forks look like drinking straws.
these are not just my opinions read up on any modern bike design or sports bike magazine etc. front wheel loading is the key here.

I about crapped my pants watching the times where the wobble gets so bad that the rider's feet came off the footrests!

Showed my 16 yr old son that video. He couldn't believe it. I agree, the feet off the pegs was definitely the worst bit!

Quite often what you feel is at the front of the bike, comes from the rear. I've had crashing, lock to lock tank slappers on three occasions, and twice got flicked over the front by not letting go of the bars quickly enough. The hydraulic steering damper will usually stop it from happening unless the bike is really badly set up. If you immediately let go of the bars when it happens, and grab the tank to stay on the bike, you will find you have plenty of time to grab the bars again- but don't do it too quickly. It is very deceptive - what can appear to be a mild shaking of the steering head can launch you off the bike. Try to keep your sense of humour and don't react too quickly, if you fight it you are gone.

comnoz said:

McDonalds has the answer to high speed weave. Eat more.

http://www.youtube.com/watch?v=z3OQTU-kE2s

Click to expand...

Jim - There was a guy we rode with in the early 80s who was, shall we say, generously proportioned. He never complained about instability on any bike and he was also probably the quickest of all of us back then. I bet he'll smile when I send him that link...

Dave

I weigh 250 lbs and I can provoke a weave on my '73 750 by sitting forward and upright and I can make it go away by moving my ass back or by entering a corner. When I ride fast, I ride with my weight forward but as the speed rises I move my weight to the rear. Coincidentally, that also results in the "laying on the tank" that the linked video recommends. Admittedly, my interpretation of "moving weight to the rear" may well be "laying on the tank"


Back in 1971 my '71 750 would weave on 4.10 Avon GPs and on 4.10 K81s as well. The best combo was 4.10 rear and 3.60 front - no weave but steering a bit quick. Nowadays I run a fat tires on both ends and put up with the threat of an occasional weave that I preemptively kill with weight shift/laydown as speeds rise.

The comment about modern bikes' forward weight bias is true but I differ a bit about why and the implications.

The main reason for designers taking weight off the rear and moving it forward is to enable more power to be put down by the rear wheel. The new bikes have wider wheels for the same reason - to put down their greater power and keep traction at far greater speeds/loads. The wider wheels, in turn demand quicker steering, greater mechanical advantage, so that means less trail and less head angle and less diameter as well.