weave / wobble?

Question

HI there i'm doing a project on weave and wobble on my advanced instructor course and was given this as my project. but theres not to much info about it and what bits there are would take about 2 mins to tell and could do with and video clip of this any info would help many thanks Ram

Answer 1

weave is associated with the rear of the bike self steering, this is caused by loadings on the rear suspension, the unsprung mass damping and the length of the swing arm.
wobble is due to the front fork rake/ caster angle front suspension type damping and headstock bearings.
Change the bikes CoG and this can have serious effects on the possibility of both occurring.
Both occur naturally on a bike but the design and construction are made to reduce this from the start. Install a fairing or fixed luggage and you can dramatically alter the characteristics of the bike. change the airflow over the rear of the bike can alter the loading on the rear suspension and off load the swing arm, thus reducing traction nad increasing weave. decelerate and the bike loads the front fork increasing the spring pressure. incorrect damping can cause the suspension to unload and the rake angle then changes, then causing the bike to wobble.
When cornering the two wheels travel on different tracks the rear wheel is on a tighter radius than the front hence counter steering ( see cinder track racing) increase the lean angle increases the degre of counter steer and the rear wheel starts to drift. expert racers use this to their advantage. on exiting the corner ( past the vanishing point) the rider throttles up unloading the front suspension but loading the rear when it is still in a slide. the sideways action and grip cause the bike to weave until the damper catches up and equalises the loading front and rear. incorrect steering damping at this point can lead to a tank slapper of a wobble of the handlebars.
Motorcycling is the use of certrapetal force as opposed to centrifugal force.
Dont forget the engine either. inline engines that run fron front to back as per Triumph rocket BMW twins Guzzi's etc they produce latteral forces in translation that are rotational about the axis of the crank at 90 degrees to the crank. IE the engine rotation causes the bike to respond by either turning into the acceleration or out if it. Transverse engines GSX CBR bandit Blade Fazer etc have the same rotational force but this relates to movement from either left to right of the bike so throttle responce causes the bike to tilt over.
additionally single sided swing arms also have an impact if the swing arm is on the lefthand side of the wheel the bike will fall into left hand bends and try to climb out of righthand bends.
As such it bothers me why manufactures who make transverse inline multis don't have contra rotating crankshafts with single sided swing arms as this will equalise the forces exhibited on the bike. BMW have taken this on board but they still haven't got it completly right yet!!!
Riding a bike is like flying and is more akin to a helicopter than a plane or more precisely more like flying a plane with a rotary engine as opposed to either an inline or radial engine

Answer 2

The old three cylinder, 2 stroke Kawasakis were notorious for wobbling due to a frame that resembled a wet noodle. There were two big causes, the first was a very steep fork angle and when coupled with the all too common Jap flexi-flyer frame, away she went. Attaching a hydraulic steering dampener to the fork help as did replacing the rear shocks with something that actually dampened the bounces. Mounting trunks up high can also cause a wobble, as soon as I put mine on my KZ 1000, I got a mild, not dangerous but still unsettling wobble.

There's probably five main causes, a steep fork angle combined with a limber frame. The angle itself isn't the cause, but the limber fram allows the fork to flex back and forth and round and round. All this changes the steering geometry. Poorly dampened rear shocks allow the rear end to spring up and down which also increases and then decreases the fork angle. Anything that raises the center of gravity and can catch the wind is another cause. The fork itself flexing can be a culprit. Many Kawasaki ZG 1200 Voyager owners install a fork brace that fits above the fender and supposedly helps stop that foolishness. Last but not least is the rear tire, not only being worn but even new tires with different tread configurations and made by different manufacturers change the way a bike tracks through corners and handles bumps and holes.

Answer 3

Most bike s today do not have this problem because the poor steering geometry and frame design that caused these problems are a thing of the past except for just once in a while.
I have to take issue with the comment above that bikes with inline crankshafts are likely in some way to be unstable due to the rotational forces of the crankshaft. I have owned several Guzzis and ridden many BMWs and neither brand was affected in this way in the slightest. The BM boxers were not good handlers and weaved badly at quite low speeds - 150kph - because of frame design, but the Guzzis and the BM Ks were very good and were never a problem.

Answer 4

Regarding PhilipP's answer, Guzzi's do not weave or wobble. Also, some good precice handling bikes were known to "white line" which would give similar symptoms to a bad handling bike, except that it was simply a loss in traction caused by slipery wet road line, and unpredictability of which way the wheels will slip (if driving in a straight line).

Answer 5

yea on the '97-'01 electra glides, there is a stabilizer that is missing on the rear of the bike. at high speed turns, the swingarm wants to go 1 way and u the other...but the bike develops a wobble instead that can quickly become fatal. i cant remember the name of the company either...it's either true track or straight track...they sell a stabilizer kit to deal with this problem. seems this isnt just affecting the e-glide, but some of the softails have this quark as well as the road kings also.

Answer 6

there were reports of harley dresser's having this wobble problem. the glides and road king's. problem was that there is a stabilizer bar that is on the dyna, softail, and sportster models, but is missing on the glides. at high speed....roughly 85 mph or over, the back tire gets squirrly, the bike starts to shake, become extremely hard to control, and could just get away from u in a split second.

i cant remember what company makes it, but there is a product that solves the missing stabilizer bar and the high speed wobble problem. yanno what sucks....the moco fully knows the problem, but has yet to advise of the cure. meanwhile, those that attempt to ride these bikes 90 mph are finding out a potentially lethal surprize....and this high speed wobble has killed alot of riders already.

Answer 7

Yer the Pan European (Honda ST1300s) some Police forces use had to be temporarily withdrawn earlier in the year. because of a couple of high-spreed crashes caused by a wobble... apparently down the the heavy loading and weight distribution. (see link)

Some bikes have oil-or-friction based steering dampers to correct this short of thing, you'll find it is often down to aggressive steering geometry (ie steep fork angle), small diameter or out-of-balance or worn tyres, tyre pressures etc etc as well as badly distributed loading or luggage.

Answer 8

http://search.yahoo.com/search?p=speed+wobbles&fr=yfp-t-471-s&toggle=1&cop=mss&ei=UTF-8