The nail may have saved your life, gggGary!
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Geometry, rake, handling, high speed wobble & weave
- Thread starter Bjorn
- Start date
My '74 TX650, full tank, single Fr. disc, luggage rack.
Front: 98kg / 216lb / 47%
Rear:110kg / 243lb / 53%
Total: 208kg / 459lb
Bjorn's: 198kg _ 435lb
Great info, i love this forum. Do the weight bias is not very different compared to the stock bike. Good to know.
Thanks for sharing all the detailed info about the head stock bearings. I'll dig into that. But on the other hand I find it hard to believe that the slightest change in preload of the bearings would completely change the bikes handling. Think about it, that would mean a motorcycle shop would basically have to be run by surgeons haha.
Like the buell Gary! I like odd bikes. But a daily would need to be reliable. I already have the XS
Thanks for sharing all the detailed info about the head stock bearings. I'll dig into that. But on the other hand I find it hard to believe that the slightest change in preload of the bearings would completely change the bikes handling. Think about it, that would mean a motorcycle shop would basically have to be run by surgeons haha.
Like the buell Gary! I like odd bikes. But a daily would need to be reliable. I already have the XS
Im 75 kg (165 lbs).Looong story but yes it's now a daily and other considerations aside, the bike I'm most likely to pick for a ride.
your weight? Unless you're big guy; 35 in the rear might be a little hard? front sounds "about right"
I've kinda headed towards 30 front and rear on the XS's
notchy races on ball bearing are SO common.... Would that contribute? mebby once races have been diturbed.
Those later yamaha stem nuts use a rubber bushing between the nuts and a retainer to lock in the setting.
I think the idea is to avoid changing preload when locking with the second nut.
View attachment 358381
O believe My head stock arrangement has one of those rubber rings between the 2 collar nuts. But its not completely original. The lower triple with stem is oem Yamaha R6, but the upper triple is custom.
Charles13
XS650 Addict
I totally agree; my Supermoto constantly had very loose steering head bearings (from all the long wheelies) and would still top out at over 100mph with no ill effects from the loose head bearings.
Just did a small testride. O lowered the rear tire pressure to about 2,1 bar. With the stock fender
Result: no noticeable difference. Still shaking and unstable at high speeds. Wasn't able to reach over 130 kmh due to traffic.
Result: no noticeable difference. Still shaking and unstable at high speeds. Wasn't able to reach over 130 kmh due to traffic.
And I checked the weight distribution with me on it.
(Without me)
Front 47%
Rear 53%
With me on it, in riding position:
Front: 42%
Rear: 58%
Next up: different front tire.
(Without me)
Front 47%
Rear 53%
With me on it, in riding position:
Front: 42%
Rear: 58%
Next up: different front tire.
Notice my drawing.
With me on it, CG is shifted forwards and up.
I do not get any wobbly or weave unless the front is unloaded/rear loaded, during hard accels.
XS's are a lot laid back style of bike so no real comparison.
Just food for thought.
Any critique on the book?
cliff
I did some reading and investigation and leaned about Wobble & weave. I dont think i've been using the terms in the right way. Here is a summary of the two phenomenonns. Info from the book of Tony Foale, Cycle world and continental:
Wobble:
Wobble is the rapid oscillation at 8–10 cycles per second of the front caster. Wobble typically occurs in the speed range of 35–40 mph, often in step with front wheel rotation and can be excited by front-wheel imbalance or out of round. Riders of some bikes experience a bit of wobble if they take both hands off the bars in this speed range to adjust gloves or face shield. In most cases, the damping effect of putting their hands back on the bars causes this to die away. Wobble damping increases with speed.
Its a harmonic motion, think of a pendulum of a clock. The front wheel can be started by external forces such as road irregularity. The restoring torque created by the trail happens to be strong enough to over-correct the initial disturbance.
Tips for reducing wobble (tony foale):
Weave
Weave is often considered an oscillation of the rear steered mass (the main part of the bike and the rider) about the steering axis. its a much more complex form of instability, because there is a lot more cross coupling between the various degrees of freedom of possible motions.
Weave is the slower side-to-side swing at 2–3 cycles per second of the rear caster. All motorcycles have a weave threshold, but care is taken in design to place this above the machine's top speed. Despite this, the addition of extra equipment, changes in loading, wear of tires, or loosening of pivots can lower this threshold, making weave possible.
The phenomenon usually appears from 120 km/h / 75 mph depending on the type of motorcycle and environmental conditions (especially wind can cause High-Speed Weave). The weave often starts after a prolonged period of riding at a constant speed and becomes more severe as the speed increases. It can only be stopped by reducing the throttle, whereas the amplitude increases with increasing speed.
Tips for reducing weave/ Contributing factors:
Sources:
Wobble:
Wobble is the rapid oscillation at 8–10 cycles per second of the front caster. Wobble typically occurs in the speed range of 35–40 mph, often in step with front wheel rotation and can be excited by front-wheel imbalance or out of round. Riders of some bikes experience a bit of wobble if they take both hands off the bars in this speed range to adjust gloves or face shield. In most cases, the damping effect of putting their hands back on the bars causes this to die away. Wobble damping increases with speed.
Its a harmonic motion, think of a pendulum of a clock. The front wheel can be started by external forces such as road irregularity. The restoring torque created by the trail happens to be strong enough to over-correct the initial disturbance.
Tips for reducing wobble (tony foale):
- Increase lateral fork stiffness
- reduce trail (to reduce the torque introduced by the trail), there are limits to this approach as it may impair directional stability.
- reduce the mass of the front wheel and fork. to reduce the moment of inertia about the steering axis. This cuts down the energy in the oscillation parts for a given magnitude and frequency of wobble. This raises the system's natural wobble frequency, making it easier to damp.
- fit hydraulic steering damper.
Weave
Weave is often considered an oscillation of the rear steered mass (the main part of the bike and the rider) about the steering axis. its a much more complex form of instability, because there is a lot more cross coupling between the various degrees of freedom of possible motions.
Weave is the slower side-to-side swing at 2–3 cycles per second of the rear caster. All motorcycles have a weave threshold, but care is taken in design to place this above the machine's top speed. Despite this, the addition of extra equipment, changes in loading, wear of tires, or loosening of pivots can lower this threshold, making weave possible.
The phenomenon usually appears from 120 km/h / 75 mph depending on the type of motorcycle and environmental conditions (especially wind can cause High-Speed Weave). The weave often starts after a prolonged period of riding at a constant speed and becomes more severe as the speed increases. It can only be stopped by reducing the throttle, whereas the amplitude increases with increasing speed.
Tips for reducing weave/ Contributing factors:
- wheel alignment
- weight distribution
- Improper maintained steering head bearings and fork
- Tyre's have a great influence, they are the main source of yaw damping in this situation.
- Tyre size
- rake and trail
- riders weight (made mainly of soft tissue, we are large internal energy absorbers)
- steering damper (to a lesser extend)
- increase chassis stiffness
Sources:
- https://www.cycleworld.com/motorcycle-wobble-and-weave-making-sense-death-wobble-talk/
- https://www.continental-tires.com/nl/nl/tire-knowledge/motorcycle-stability-issues/
- Motorcycle handling and chassis design (tony foale), stability and control.
here is a very interesting video about wobble and weave (by Dunlop). Note its from the era of the XS 650.
I feel that my problem is more a Weave, than a Wobble.
My bike does not show a lot of the signs of a wobble. Its not at lower speeds, i can let go of the bars during deceleration without any problems. As shown below:
I think its a Weave problem. It has most of the signs. At higher speeds, at constant speeds, the motion feels like described above. like the whole bike is twisting. I actually did some testing this weekend together with a buddy. By switching bikes I saw my bike move like the Dunlop video above!
Back to what I've changed and tested:
My bike does not show a lot of the signs of a wobble. Its not at lower speeds, i can let go of the bars during deceleration without any problems. As shown below:
I think its a Weave problem. It has most of the signs. At higher speeds, at constant speeds, the motion feels like described above. like the whole bike is twisting. I actually did some testing this weekend together with a buddy. By switching bikes I saw my bike move like the Dunlop video above!
Back to what I've changed and tested:
- changed the front tire to a Bridgestone BT 46 100/90-19.
- Steers slower compared to the Michelin road classic tire, especially at lower speeds.
- Bike feels more stable at highway speeds. Not mega, but definitely moving in the right direction.
- Giving the handle bar a steering input at 120 kmh, it weaves for a bit and disappears (not increasing or self sustaining)
- My buddy is heavier and did not experience the bike starting to weave on its own up to 145 kmh.
High speed run, up to about 140kmh. The bike does not start a weave by itself.
I also talked to a local XS specialist (Jerry vd Heiden) and asked him about my situation. He said that the XS is not known for its stability. So maybe I should see things in perspective.
My goal is be able to safely ride on the highway at higher speeds if I choose to do so. There are some things I would like to try to improve the stability even more:
- reduce unsprung weight
- try a steering damper (even though its not supposed to be a fix all solution for weaving...)
- Try a lower rear tire. Running 120/80-18 now, I just discovered there is a 130/70-18 option. Maybe anyone can chime in regarding the clearance.
- Im leaving the rake and offset where they are for now. Changing them is very involving with making new triple clamps.
- increase chassis stiffness. I find this topic interesting! I want to split it up in two things:
- chassis stiffness: found some interesting articles from Tony regarding a kawa 750: https://motochassis.com/Articles/Frame.mod/KawaMods.htm. I did some research on the forum but could not find a lot of images of people reinforcing the stock frame. Maybe anyone has some tips?
- swingarm stiffness: Making a fully custom swingarm is on my list for a long time. Its quite a project but might be nice to take this stiffness into the new design
Not sure if this will help you much. When I built my last XS2 I strengthened frame a little. It's a early frame so what I did may not be relevant to your frame. When I resurrected my original XS2 I found the frame broken in several places and cracked in several. I should add the engine cases were cracked also. Early frames are known to flex. This is my original original XS2 frame.
So when I built my "Rally" bike I decided to reinforce the frame and try to get it stiffer. Welded in some pieces.
Added another cross member.
Also a couple of gussets. One on each side.
Also tied the front down tubes together at the front motor mount. I've done this on several other early frames. The pic is from another early frame.
Of all 3 of my XS2s this one feels the most stable at higher speeds. At the Ozarks last year I had it over 90 mph several times. Felt solid as a rock. Roads down there are very smooth.
So when I built my "Rally" bike I decided to reinforce the frame and try to get it stiffer. Welded in some pieces.
Added another cross member.
Also a couple of gussets. One on each side.
Also tied the front down tubes together at the front motor mount. I've done this on several other early frames. The pic is from another early frame.
Of all 3 of my XS2s this one feels the most stable at higher speeds. At the Ozarks last year I had it over 90 mph several times. Felt solid as a rock. Roads down there are very smooth.
I was able to borrow a steering damper for testing. made a quick bracket and did some testing today. I played with the adjustable damping. From high to low.
Result: it does not bring any improvement to the unstable feeling at high speed.
This confirms the theory that my problem is most likely "high speed weave" and not "high speed wobble". Since the info described that a steering damper usually doesn't improve the high speed weave situation.
At least I don't have to spend money on a steering damper hehe.
Result: it does not bring any improvement to the unstable feeling at high speed.
This confirms the theory that my problem is most likely "high speed weave" and not "high speed wobble". Since the info described that a steering damper usually doesn't improve the high speed weave situation.
At least I don't have to spend money on a steering damper hehe.
Im late to the party here, but if it helps I have used parts from Cognito Moto in the USA.
They are incredibly helpful and have top quality soloutions to all build issues.
It may be worth a look here: https://cognitomoto.com/collections/xs650
They are incredibly helpful and have top quality soloutions to all build issues.
It may be worth a look here: https://cognitomoto.com/collections/xs650
Far more knowledgeable and experienced folks than myself have chimed in here, but I'll had my two bits... what strikes me in your initial data is the difference in offset between the stock XS triples and your R6/custom triple. I have an XT350 that has a sportbike forkset on it with much-less-than-stock offset (done by a PO). It too feels unstable at higher speeds but rarely gets ridden fast enough for it to be an issue. Could that be a factor, regardless of the very similar trail figures?
Offset is just part of the geometry. Together with the rake angle of the fork and the tire diameter, it determines the trail for the motorcycle.
Im not 100% sure why certain offset values are chosen. It might follow other parts of the motorcycle. For instance having low offset values, could mean that the forks hit the frame/tank at maximum steering angle.
Since my trail is comparable to the stock value, and its kinda involving to change it. In sticking with it for now.
Its kind of an annoying problem to be honest. Hopefully the modifications i plan on doing this winter will help. And there is not a lot of info to be found on high speed weave. And even less info regarding the fixing of it. Most info is about stock motorcycles, not Modified ones
Im not 100% sure why certain offset values are chosen. It might follow other parts of the motorcycle. For instance having low offset values, could mean that the forks hit the frame/tank at maximum steering angle.
Since my trail is comparable to the stock value, and its kinda involving to change it. In sticking with it for now.
Its kind of an annoying problem to be honest. Hopefully the modifications i plan on doing this winter will help. And there is not a lot of info to be found on high speed weave. And even less info regarding the fixing of it. Most info is about stock motorcycles, not Modified ones
Hey Dave, no I have not.
But i recently was at a motorcycle suspension shop for new shocks. I took the opportunity to ask them about the whole setup, including my Headstock bearings. Their opinion was that my bearings feel fine. Including the friction/resistance.
I asked them about ball bearing VS tapered bearings. They were not really in favour of one. Just mentioned that tapered bearings will not "dent" as quickly.
So changing my Headstock bearings from ball to tapered rollers is not very high on my list.
But i recently was at a motorcycle suspension shop for new shocks. I took the opportunity to ask them about the whole setup, including my Headstock bearings. Their opinion was that my bearings feel fine. Including the friction/resistance.
I asked them about ball bearing VS tapered bearings. They were not really in favour of one. Just mentioned that tapered bearings will not "dent" as quickly.
So changing my Headstock bearings from ball to tapered rollers is not very high on my list.
sparky4123
IN XS
I think most will agree that the tapered head bearings are far superior to the original ball bearings. Big increase in the contact area of the rollers. My ‘76 which is basically stock, Avon Roadriders, tapered bearings set correctly, fork brace also starts to feel a bit unstable on the freeway above 115/120. I think the weave could be partially caused by the wide bars and sitting upright like a big sail on the bike. Any buffeting winds caused by other vehicles going in your direction don’t help matters. Hey, it’s an old bike and was never designed for high speed cruising. You wanna go fast it’s safer on a newer bike designed for that.
