Commando weave

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I read this thread and what I saw in that video were hardly examples of a 'weave', more like tank slapper wanna-be's. I've never had any of my bikes misbehave that badly. The sort of weave I've suffered is what happens if your steering stem bearings are a bit tight or maybe a bit worn so they want to 'stick' a bit. It becomes hard for the bike to self-center and you find yourself continually making very small course corrections. Surely this kind of problem is due to the effective geometry being nowhere near the designer's intent?
 
I just wonder what @Jeandr experienced with his 21" wheels setup...

As for me, I've owned 171 bikes, and ONLY ONE almost killed me due to a 70MPH SERIOUS tank-slapping wobble/weave. It was a '75 T160 Trident with aftermarket alloy wheels that had been very nicely laced with stainless spokes, but NOT properly tensioned. All of the rear spokes were loose!!!

I tried gently easing off the throttle - wobble got worse. I tried accelerating slightly, wobble got even WORSE, to the point of the tire leaving 20' long opposing arcs on the pavement that I saw on my return trip. I eased (not easily) the bike over to the shoulder and expected to be thrown off into the grass on the verge, but the different road surface apparently calmed the bike down and that was that. I rode home at about 50MPH.

Out of 19 Commandos I've restored or refurbished including tire brands besides Avon (RoadRunners & RoadRiders), and 4 others that I've owned and made tire, isolastics, and other related changes to, NONE have exhibited weaves, wobbles, or any type of unexpected behavior.

For the unbeliever(s), the above is ALL factual. I am not attributing ANY of it to ME personally, just to the specific bikes I have owned, and/or worked on.

For @BillT this includes Chip's bike; which, when I test rode, did NOT exhibit the tail-shake due to the knackered swingarm spindle tube that I overlooked. Admittedly, I don't think I took it to 100MPH, which I SHOULD have (I did on my first client's Commando, and it, too was fine).

Pure coincidence? Don't know, can't say.

--- Some bikes have/had Taylor head steadies, ALL have/had new vernier adjustable isolastics, some had NJB shocks, some had IKONS, some had Emgo, some had Hagon. Propbably not all had the same rear shock position set. At least 2 of the pre-MkIII bikes had MkIII head steadies...
 
If you Google "tank slapper" you'll get a LOT of hits referencing articles and videos on the subject. It's certainly not new, and not limited to vintage machines. I dunno if there's one thing that contributes to it more than others. Just look back on this thread and see the variety of "solutions" that folks have come up with, everything from different rims and tyres to loose spokes. Maybe it's as 850commando's professor said - motorcycles are inherently unstable.
 
Regarding tank slappers, I’ve mentioned this before but will repeat here:

I had a GSXR 750 Slingshot when they first came out (‘88?) and Performance Bikes ran an article on how to set up the front forks according to Mick Grant.

This involved dropping the forks through the yokes 1/4” or so, setting the preload and damping as per, and changing the quantity and type of fork oil.

The fork legs had no drain screws, necessitating a full front end strip down to drain. I was 20 years old, and this wasn’t gonna happen.

So I did all the mods but left the oil as stock.

The only noticeable difference was that, under certain circumstances, it would go into a violent tank slapper! On one particularly memorable ‘canter’ along with a ‘hoover pipe’ ZXR 750, I hit some bumps at 130mph and the thing went into a full lock to lock slapper. I only stayed on by the grace of God. The slapper was so violent I bruised my knees on the fairing and thighs on the tank. I absolutely shat myself and put it all back to stock as soon as I’d crawled home at 30mph!

My (eventual) point is... I was amazed how such little changes turned a first rate handler into a death trap.
 
My MK3 behaves perfectly to an indicated 110 mph. Just moving my feet from the front pegs to the passenger pegs will bring on a slow weave at 70 mph. I tried speeding up to 80 and the weave just increased. It didn't seem wise to try 90 or higher!
The solution was to put my feet back on the front pegs.
Sometimes on a long trip it helps with comfort to shift to the rear pegs for awhile. I still do that occasionally, knowing that the weave will show up.

Glen
 
worntorn said:
My MK3 behaves perfectly to an indicated 110 mph. Just moving my feet from the front pegs to the passenger pegs will bring on a slow weave at 70 mph. I tried speeding up to 80 and the weave just increased. It didn't seem wise to try 90 or higher!
The solution was to put my feet back on the front pegs.
Sometimes on a long trip it helps with comfort to shift to the rear pegs for awhile. I still do that occasionally, knowing that the weave will show up.

Glen
Click to expand...
That is exactly my experience as well. Putting my feet back on the passenger pegs to stretch my legs on the highway will create a weave at 65-70. Sometimes I get a leg cramp while on a long ride and that can help stretch the old muscles, being aware of the consequences. Other than that, only the hands-off-at-35 mph weave has annoyed me, and that goes away with new tires.
 
Interesting that putting feet on rear footrests should cause a weave, mine doesn't do that and I often put my feet on the rear legs to avoid discomfort
Funny how small things can make a difference
 
worntorn said:
My MK3 behaves perfectly to an indicated 110 mph. Just moving my feet from the front pegs to the passenger pegs will bring on a slow weave at 70 mph. I tried speeding up to 80 and the weave just increased. It didn't seem wise to try 90 or higher!
The solution was to put my feet back on the front pegs.
Sometimes on a long trip it helps with comfort to shift to the rear pegs for awhile. I still do that occasionally, knowing that the weave will show up.

Glen
Click to expand...
Strange. I did that (feet on pillion pegs to rest) on my MkIII and never got a weave cruising at 80 (not any speed). Original Dunlop K70 TTs
 
Fast Eddie said:
Regarding tank slappers, I’ve mentioned this before but will repeat here:

I had a GSXR 750 Slingshot when they first came out (‘88?) and Performance Bikes ran an article on how to set up the front forks according to Mick Grant.

This involved dropping the forks through the yokes 1/4” or so, setting the preload and damping as per, and changing the quantity and type of fork oil.

The fork legs had no drain screws, necessitating a full front end strip down to drain. I was 20 years old, and this wasn’t gonna happen.

So I did all the mods but left the oil as stock.

The only noticeable difference was that, under certain circumstances, it would go into a violent tank slapper! On one particularly memorable ‘canter’ along with a ‘hoover pipe’ ZXR 750, I hit some bumps at 130mph and the thing went into a full lock to lock slapper. I only stayed on by the grace of God. The slapper was so violent I bruised my knees on the fairing and thighs on the tank. I absolutely shat myself and put it all back to stock as soon as I’d crawled home at 30mph!

My (eventual) point is... I was amazed how such little changes turned a first rate handler into a death trap.
Click to expand...
Which is exactly why I bought a ZXR - notwithstanding my previous experiences with a Z1R. Gixxers were nervous enough without 'assistance'.
I was 'in the business' around this time, and I did quite well among the Ernest Scratcher brigade by carefully returning their multi-adjustable suspension back to factory settings after they'd done their worst with them, in the search for... whatever it was they were looking for!
 
As mentioned, just slight changes can make a big difference. The only change I can think of that stopped my '68 Commando from being scary obove 80mph was changing the bars. Nothing else seemed to have any effect. It would appear from the Dunlop film that rider weight & height play a role in how a given bike will handle. I'm 6'1" & 13.5 stone (189lb) but if I was 5'10" & 16 stone would my bike have weaved? Should Norton have listed deep sea divers weights as optional equipment?
 
A stock motorcycle with that behavior is more of an amusement ride than an actual vehicle for transportation. Seems like a move to increase trail would help quite a bit. Back to choppers!
 
I've experienced more than a couple weaves, one decades ago on a 1970 XS650 was a "near death" event. Got lucky that time and found a rider band-aide that has always worked for me since. Pushing forward against both hand grips. Conversely pulling back on the handlebars will likely increase a weave. If you have a bike that exhibits gentle weave you can experiment a bit to see what I mean. In addition to pillion riders, gear carried back and high tends to increase weaves. ie tank bags and saddlebags are better luggage solutions than tail packs. Enjoyed reading this thread as I just got a set of wheels, Akront WM 18x2.50 rims laced with stainless spokes on commando hubs, unfortunately the installed brand new tires are 25 years old. :confused: cleaned up now, they look quite charming in the shop. Still debating installing them on the combat. Bearings are stuffed from sitting and need replacing also.
 
gggGary said:
I've experienced more than a couple weaves, one decades ago on a 1970 XS650 was a "near death" event. Got lucky that time and found a rider band-aide that has always worked for me since. Pushing forward against both hand grips. Conversely pulling back on the handlebars will likely increase a weave. If you have a bike that exhibits gentle weave you can experiment a bit to see what I mean. In addition to pillion riders, gear carried back and high tends to increase weaves. ie tank bags and saddlebags are better luggage solutions than tail packs. Enjoyed reading this thread as I just got a set of wheels, Akront WM 18x2.50 rims laced with stainless spokes on commando hubs, unfortunately the installed brand new tires are 25 years old. :confused: cleaned up now, they look quite charming in the shop. Still debating installing them on the combat. Bearings are stuffed from sitting and need replacing also.
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Do not use 25 year old tyres.
 
Yeah got the wheels at a "throw away the tires" price. Which is prolly what'll happen, maybe after a top speed wobble check run. :cool: You want to visit a timesink: research PIO (pilot induced oscillation). It's a big part of how weaves can get violent. The push instead of pull thing is way of removing musclo/skeletal feedback from control inputs.

Commando weave
 
gggGary said:
Yeah got the wheels at a "throw away the tires" price. Which is prolly what'll happen, maybe after a top speed wobble check run. :cool: You want to visit a timesink: research PIO (pilot induced oscillation). It's a big part of how weaves can get violent. The push instead of pull thing is way of removing musclo/skeletal feedback from control inputs.
Click to expand...
Divergent Oscillation in Pitch, Dutch Roll, Phugoid all personallly experienced at 12000 ft courtesy of the Empire Test Pilot's School. Amusingly the only guy who got sick was ex RAF.

I think the issue is the Commando seems to exhibit some unique handling traits which don't fit the category of tank slapper. The weave I experienced was just a very low-cycle oscillation of less than 1Hz, and never experienced on any other brand. I doubt that a steering damper would have much effect.
 
I hopped on the wife's Virago years ago and nearly went on my ass. The bike had not been ridden in about three years and the tires were 'elderly'. They evolved into a sort of wood with no traction whatsoever. I can't remember the exact age of them, but it was way less than 25 years.
 
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