Commando weave

baz · Dec 11, 2020

When I built my commando many years ago I fitted a pair of apprillia pegaso 650 wheels ,yam fz750 forks /yokes MK3 cotter pin conversion on the swing arm which is also over braced and under braced
An extra iso under the gearbox ,koni rear shocks norvil head steady , gearbox cradle bolt holes reamed to fit crankcase
Chassis set up on a surface plate
I was a bit pissed off to find it weaved at high speed
After many alterations which included at one point re fitting the commando forks because I thought the yam 40mm offset could be the cause eventually it turned out to be the rear tyre
I went from a 130/80/17 to and old tt100 410 X 19 and with no other changes the weaving stopped
Also along the way I tried the back wheel out of my t140e but still the weave persisted
I have always concluded that too wide a tyre or too small in diameter can cause a high speed weave all over things being equal

MexicoMike · Dec 11, 2020

I sympathize!!!

I bought my current Commando in '06 from a well known US vintage Britt-Bike seller who assured me the bike was "ready to ride across the country,", Turned out that among the many issues it had (including other serious safety issues) were grotesquely mismatched 18" wheels/ tires. It had a steering damper which, when on the heaviest setting, was able to (just) manage to make the bike rideable. I removed the wheels/tires and installed OEM wheels and 4.10/19 Roadrunners. It immediately transformed the bike and the steering damper has been removed ever since.

IMO, a word for 'upgrading' the wheels/tires on a street Commando to something other than OEM size is: "Downgrading!"

ashman · Dec 11, 2020

Commando's were designed to run with 19" wheels and came from the factory with 4.10x19 tyres front and back, but found running a 3.50 tyre on the front wheel the bike steered better in the corners, my 74 Norton had 4.10 K81s when I brought it new.

Ashley

kommando · Dec 12, 2020

The Earles Court Commando display model and the info sheet given out at the show had a rear wheel that matched the Atlas. A 18" WM3 rim, between then and the first production build it changed to 19" WM2.

baz · Dec 12, 2020

MexicoMike said:
I sympathize!!!

I bought my current Commando in '06 from a well known US vintage Britt-Bike seller who assured me the bike was "ready to ride across the country,", Turned out that among the many issues it had (including other serious safety issues) were grotesquely mismatched 18" wheels/ tires. It had a steering damper which, when on the heaviest setting, was able to (just) manage to make the bike rideable. I removed the wheels/tires and installed OEM wheels and 4.10/19 Roadrunners. It immediately transformed the bike and the steering damper has been removed ever since.

IMO, a word for 'upgrading' the wheels/tires on a street Commando to something other than OEM size is: "Downgrading!"

I did try a steering damper ,it was one of those Kawasaki 7 position ones that everyone used to use
It made no difference to my bike weaving,just made the steering heavy
I threw it over the fence with the choke slides/indicators/center stand etc

cash · Dec 12, 2020

I've a Mk3 850 and never had a problem with weaving. I have a 18" rear wheel fitted and have used all brands of tyres 100 to 120. My mate has a near standard Mk2 850 and he has. Some of it was caused by wheel alignment and tyre pressure. Apparently the factory thought taller riders were more likely to experience the weave. I'm vertically challenged while my mate is quite tall. I wonder if its something strange, perhaps the way the rider holds the handlebars you know stffly, lightly? And I know from personal experience fitting different yokes can cause big handling problems.
Dave

Matchless · Dec 12, 2020

My '68 750 had serious handling problems when I first aquired it. It was fitted with a 18" rear wheel & a 120 section tyre. It was never very happy over 75/80 mph & would go into a weave, On the way home from work one evening I headed towards the country lanes & on leaving a village rode over those bloody stupid red rumble strips. As I accelerated it went into a serious tank slapper. After that I didn't trust the bike. I checked the wheel alignment, tightened up the ISOs etc but couldn't find anything wrong.
I had a chat with Martin Russell (Rustler Racing) & he thought the rear wheel was causing the problems, & so I fitted a 19" rear with a 100/90/19 Avon. It wasn't nuch better. The next step was Maxton suspension front & rear but still no better. What finally fixed it was changing the handlebars for a pair with a two inch rise as opposed to the Norton flats. It's now a great handling bike.
I fitted a 18" rear to my 920 purely to get better tyre life, & whilst it is totally stable it doesn't feel as nice as when it was fitted with the 19" rear.

Martyn.

Fast Eddie · Dec 12, 2020

Avon 18” rear / 19” front combo that I use both have a diameter of 26.4”. The 4.10 / 19 Roadrunner has a diameter of 26.3”.

baz · Dec 12, 2020

Matchless said:
My '68 750 had serious handling problems when I first aquired it. It was fitted with a 18" rear wheel & a 120 section tyre. It was never very happy over 75/80 mph & would go into a weave, On the way home from work one evening I headed towards the country lanes & on leaving a village rode over those bloody stupid red rumble strips. As I accelerated it went into a serious tank slapper. After that I didn't trust the bike. I checked the wheel alignment, tightened up the ISOs etc but couldn't find anything wrong.
I had a chat with Martin Russell (Rustler Racing) & he thought the rear wheel was causing the problems, & so I fitted a 19" rear with a 100/90/19 Avon. It wasn't nuch better. The next step was Maxton suspension front & rear but still no better. What finally fixed it was changing the handlebars for a pair with a two inch rise as opposed to the Norton flats. It's now a great handling bike.
I fitted a 18" rear to my 920 purely to get better tyre life, & whilst it is totally stable it doesn't feel as nice as when it was fitted with the 19" rear.

Martyn.

I once owned a Kawasaki that only had one mirror and the bike would weave at high speed
Out of interest I tried twisting the mirror 90° and it completely stopped the weaving, so a matching pair of mirrors were fitted and no more issues

Matchless · Dec 12, 2020

Fast Eddie said:
Avon 18” rear / 19” front combo that I use both have a diameter of 26.4”. The 4.10 / 19 Roadrunner has a diameter of 26.3”.

It's not the diameter that's the problem but the width. Many moons ago my mate Andy had a Z1B to which he fitted a 120 section tyre & it wrecked the already not great handling. I fitted a 110 section for him & the weaving problem went away. Some bikes are really very tyre sensitive. A ccouple of years ago I fitted a pair of Michelin tyres to the 920 & guess what? It weaved badly at 70+ so I fitted a Roadrider on the rear only & normality was restored.

baz · Dec 12, 2020

Matchless said:
It's not the diameter that's the problem but the width. Many moons ago my mate Andy had a Z1B to which he fitted a 120 section tyre & it wrecked the already not great handling. I fitted a 110 section for him & the weaving problem went away. Some bikes are really very tyre sensitive. A ccouple of years ago I fitted a pair of Michelin tyres to the 920 & guess what? It weaved badly at 70+ so I fitted a Roadrider on the rear only & normality was restored.

I agree, I'm pretty sure it's more the width of the tyre causing tyre squirm
Similar can happen with any bike that does lots of motorway miles when the tyre scrubs square

maylar · Dec 12, 2020

Define "weave" please, for the uninitiated. I've experienced the 35 mph hands off head shake and the infamous Commando left lean syndrome, but I wouldn't call either a weave. What are you guys referring to?

kommando · Dec 12, 2020

SteveA · Dec 12, 2020

Matchless said:
It's not the diameter that's the problem but the width. Many moons ago my mate Andy had a Z1B to which he fitted a 120 section tyre & it wrecked the already not great handling. I fitted a 110 section for him & the weaving problem went away. Some bikes are really very tyre sensitive. A ccouple of years ago I fitted a pair of Michelin tyres to the 920 & guess what? It weaved badly at 70+ so I fitted a Roadrider on the rear only & normality was restored.

I sort of agree and disagree with both of you. I think is the tyre sidewall and it's ability to move! An 18" tyre of the same rolling diameter as an alternative 19" tyre has deeper sidewalls!

Tyre construction may negate or exaggerate this, but then you are into comparing a large number of variables!

We know the Norton development team went from the 18" to a 19" for a reason to solve a problem identified in further testing, does anyone have written evidence of that process and definition, was it just trial and error or did they discover why the 18" was a problem?

Interesting to know, but in any case it would be rather moot when trying to assess alternative modern tyres compared to the period tyres!

My personal choice on my '70 Fastback was 3.60 front and 4.10 rear TT100 for better steering, tyre choice of the day was Dunlop TT100s or Avon Roadrunners, pretty limited.

Today I feel the limitation of using 19" wheels is tyre choice, but I really mean for racing, because I am using 19" rims on one of my race bikes (not a Norton) I am fitting Avons, whilst in 18" I normally use Heidenau which I find better in the wet.

Since a lot of road Commandos are on 100/90 x 19" Avons by owner choice, I suspect most owners would benefit from sticking to 19" rims with the proven tyres for the application!

baz · Dec 12, 2020

kommando said:

The weave on my commando was a bit more gentle than those in the video but shifting weight forward made no difference on my bike although it did feel a little bit more planted when the tank (fastback) was full

baz · Dec 12, 2020

SteveA said:
I sort of agree and disagree with both of you. I think is the tyre sidewall and it's ability to move! An 18" tyre of the same rolling diameter as an alternative 19" tyre has deeper sidewalls!

Tyre construction may negate or exaggerate this, but then you are into comparing a large number of variables!

We know the Norton development team went from the 18" to a 19" for a reason to solve a problem identified in further testing, does anyone have written evidence of that process and definition, was it just trial and error or did they discover why the 18" was a problem?

Interesting to know, but in any case it would be rather moot when trying to assess alternative modern tyres compared to the period tyres!

My personal choice on my '70 Fastback was 3.60 front and 4.10 rear TT100 for better steering, tyre choice of the day was Dunlop TT100s or Avon Roadrunners, pretty limited.

Today I feel the limitation of using 19" wheels is tyre choice, but I really mean for racing, because I am using 19" rims on one of my race bikes (not a Norton) I am fitting Avons, whilst in 18" I normally use Heidenau which I find better in the wet.

Since a lot of road Commandos are on 100/90 x 19" Avons by owner choice, I suspect most owners would benefit from sticking to 19" rims with the proven tyres for the application!

I now use 90/90/19 on the front 100/90/19 (roadriders )and there's no hint of a weave up to 110 mph

kommando · Dec 12, 2020

SteveA said:
We know the Norton development team went from the 18" to a 19" for a reason to solve a problem identified in further testing, does anyone have written evidence of that process and definition, was it just trial and error or did they discover why the 18" was a problem?

The UK tyre manufacturers would not guarantee an 18"tyre of their current late 60's design could cope with the higher speeds and loadings from both the Commando and the R3/T150 so both needed 19" front and rear tyres according to one version. They did later have 18" tyres capable but the Commando/T160 stayed with a 19" rear wheel, which suggests that tyre capability was not the sole reason for the change to 19" rear wheels.

maylar · Dec 12, 2020

I have noticed that if I put my feet on the passenger pegs while on the highway I'll get a weave. I guess that's from putting more weight in the rear. I'd do that sometimes to stretch my legs a bit during a long ride but it sure feels squirrely.

850commando · Dec 12, 2020

It would be interesting to garner some feedback from those individuals who have modified their Nortons with a much stiffened swingarm and alt forks or added bracing , I am not a suspension expert, and so i will keep my opinions to myself, (opinions are like @$$h0les... everybody get 1.. but only 1), i will add though that aerodynamics are playing into this, which are affecting the drag coefficient and Re.

tire evolution needs to be considered too.

EstuaryBoy · Dec 12, 2020

baz said:
I once owned a Kawasaki that only had one mirror and the bike would weave at high speed
Out of interest I tried twisting the mirror 90° and it completely stopped the weaving, so a matching pair of mirrors were fitted and no more issues

There's a: 'Never looked back' joke in there somewhere.......

Commando weave

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