Commando High Speed Stability

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Rohan said:
phil yates said:
My MkIII Roadster has steel wheels 19" front and rear and is rock solid in the front end all the way up and beyond 100mph.
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So, to sum up, your Mk3 runs like a dream, and you are going to change tyres because something must be wrong. ???
And a great colour scheme in excellent condition is going to be overpainted like a Velocette.
(sorry all those black-n-gold owners already out there - including me, I have tank n sidecovers in that scheme !)


Is it April 1st ??
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I'm still waiting for some questions Rohan. It's not April 1st and downsizing front tyre profile has nought to do with high speed Fastback/Roadster handling differences. I gather you have now realised your error.

Why do you criticise the suggested paint scheme then apologise to everyone including yourself???

Phil
 
in my opinion its the width of the rear tyre and whether it is scrubbed square that makes a commando weave i have run mine with a 130/70x17 back wheel battlax tyre ,a 120x18 with an avon roadrunner (admittedly the avon was worn square) these both made the bike weave badly above 80mph then a 410x19 with a tt100 and with no other changes the bike stopped weaving the front had a 410x19 roadrunner fitted ,it now has roadriders front 360 x 19 and rear 410 x 19 and rides even better no weaving up too 110 mph anyway ,,,,,baz
 
baz said:
in my opinion its the width of the rear tyre and whether it is scrubbed square that makes a commando weave i have run mine with a 130/70x17 back wheel battlax tyre ,a 120x18 with an avon roadrunner (admittedly the avon was worn square) these both made the bike weave badly above 80mph then a 410x19 with a tt100 and with no other changes the bike stopped weaving the front had a 410x19 roadrunner fitted ,it now has roadriders front 360 x 19 and rear 410 x 19 and rides even better no weaving up too 110 mph anyway ,,,,,baz
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Weaving is a totally different issue baz. I experience none of that. I'm talking about a perceptive feel issue in a sense that should you hit bumps at over 70mph, the front end feels slightly too sensitive. I believe the roadriders are extremely good tires. I'm sticking with TT100's due familiarity and the fact that I already have five of them.

Phil
 
Phil,
'I have learnt in the past, that what you don't spend of your money on Nortons, women will spend it for you on anything BUT Nortons. It is a race to the bottom.'

I'm 72 years old and these days find it difficult to find the readies to race again. I remarried about 13 years ago, and now I'm a bit philosophical. I have a fair bit of anger when I think of my previous relationship and the fact that I was conscientious and spent a lot of time studying to improve my professional competence. Overall I only have one regret - I didn't pursue my hobby strongly enough. I've always been a competent rider, and when I think about what could have been, I get upset. It is now too late for me. The message is this - while you need the experience of raising kids and all that stuff, it is imperative that you do something for yourself. Never feel guilty about playing motorbikes and having an active manhood. Enjoy your Commando, while you are still young enough and earning.
 
A while back I had a Yamaha RD250LC on the road. On a perfectly smooth road it was quite OK, however on a road with the slight depression caused by heavy trucks it was really off-putting. I raced for a fairly long time and when the bike sends me messages, I know what they mean. If your bike doesn't feel stable at high speed you need to watch yourself. In most cases the suspension pumps down and the bike becomes more stable due to the increased gyroscopic effect of the wheels (thus the need to reverse steer some bikes into corners) . If the bike feels skitterish or loose, you have a problem. Sometimes a crash can come out of the blue, totally unexpected.
 
acotrel said:
Phil,
'I have learnt in the past, that what you don't spend of your money on Nortons, women will spend it for you on anything BUT Nortons. It is a race to the bottom.'

I'm 72 years old and these days find it difficult to find the readies to race again. I remarried about 13 years ago, and now I'm a bit philosophical. I have a fair bit of anger when I think of my previous relationship and the fact that I was conscientious and spent a lot of time studying to improve my professional competence. Overall I only have one regret - I didn't pursue my hobby strongly enough. I've always been a competent rider, and when I think about what could have been, I get upset. It is now too late for me. The message is this - while you need the experience of raising kids and all that stuff, it is imperative that you do something for yourself. Never feel guilty about playing motorbikes and having an active manhood. Enjoy your Commando, while you are still young enough and earning.
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Well said acotrel.
Life is too short so enjoy what you can when you can, and never take yourself too seriously. I lost ten good years of my life plus most of what I had, followed by dreadful depression as a result. But I ain't never letting that happen again. I don't even care about money, as you've probably noticed when it comes to my Norton passion. I couldn't sleep for a week just thinking about buying my 3.60 TT100 front tyre. That's how simple I am to keep happy. And sorting minor light high speed steering issues is just fun to me.

Phil
 
acotrel said:
A while back I had a Yamaha RD250LC on the road. On a perfectly smooth road it was quite OK, however on a road with the slight depression caused by heavy trucks it was really off-putting. I raced for a fairly long time and when the bike sends me messages, I know what they mean. If your bike doesn't feel stable at high speed you need to watch yourself. In most cases the suspension pumps down and the bike becomes more stable due to the increased gyroscopic effect of the wheels (thus the need to reverse steer some bikes into corners) . If the bike feels skitterish or loose, you have a problem. Sometimes a crash can come out of the blue, totally unexpected.
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Totally agree. I too can sense messages long before things happen. I think most blokes with any time on a bike can, well I certainly hope so. Yes acotrel, the fastback has a sense of potential high speed instability should I plough into a patch of nasty bumps. At lower speeds, absolutely no problem. So I will get to the bottom of it starting with a 19" rear wheel, and work my way forward from there if necessary.

Phil
 
I will never fit less than 110 front tire again d/t lack of brake grip even on factory front brake, with nail hole of course or even 90 tire over powers pad force. Its possible that the swing arm bushes are sloppy and the tranny shafts too so the triplex chain flop can tug rythmatically on swing arm to front mount and on set a weaving hunting sense just going steady 70. Put it on center stand and tug u/d on rear chain and maybe also primary too. Pre Peel no name 1st Combat had random onsets of slight hinging front oscillation for a few months to point just about convinced me Cdo to screwy to bother with till one day farting with chains happened to notice same rhythm as on the road which got solved by swing arm and tranny bush renewal. its also possible bar height are affecting aerodynamics or seat position so need to play around to see if that matters.
 
hobot said:
I will never fit less than 110 front tire again d/t lack of brake grip even on factory front brake, with nail hole of course or even 90 tire over powers pad force. Its possible that the swing arm bushes are sloppy and the tranny shafts too so the triplex chain flop can tug rythmatically on swing arm to front mount and on set a weaving hunting sense just going steady 70. Put it on center stand and tug u/d on rear chain and maybe also primary too. Pre Peel no name 1st Combat had random onsets of slight hinging front oscillation for a few months to point just about convinced me Cdo to screwy to bother with till one day farting with chains happened to notice same rhythm as on the road which got solved by swing arm and tranny bush renewal. its also possible bar height are affecting aerodynamics or seat position so need to play around to see if that matters.
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Thanks hobot,
But it is none of these from my assessment. It's nothing beyond a sense of slight instability just as you feel in a sports aircraft but they are made to be that way. Nothing starts weaving or even feeling like it will. Just a sense of the front end not returning quickly to straight track if displaced. That is basically the definition of instability.

Phil
 
Okay, I've been beaten into submission. I won't change it. I'll paint the renovated bathroom black instead with a gold bath. And Canary Yellow floor tiles with picture of Vivian Neves embossed.
Won't I be a popular boy??

Phil
 

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Phil,
It's quite alright to throw money at a Norton. Just make sure that it gets spent wisely. The TT100 tyres are old technology. The pressures you are running are inadequate. I run alloy rims (Morad) in 2.5" x 19" both ends. With 100/90 Avon Roadriders with 34psi rear and 32psi front it has a nice light touch to the steering with absolutely no stability issues as the speed gets higher. This way, when the rear wears out, the front tyre gets fitted to the rear and the new tyre goes on the front. This will make a big difference to your handling. If I had 200 litres of kerosene I wouldn't run it in my Norton "because I already had it".

Jim Comstock's beautiful headsteady is worth the ask. Simple, neat, no adjusting. Simple to fit and does the job. Ikon shocks are the business. Made just down the road from you. Not cheap, but worth the ask.
 
The thing that's bothered me most since I bought my bike is the sense of instability when travelling at a steady speed, about 70 mph on motorways, it is particularly bad on the M1 as there is a section of road before the Berowra turnoff which has a finely 'ribbed' surface, (possibly a prelude to a resurfacing which has never happened) the front end of the bike feels oversensitive like its about to start a deathweave, there is no problem when accelerating even at much higher speeds on minor roads. I changed from Avons to TT100's (19" front and 18" rear) a narrower tyre on the front, put a Dave Taylor head steady on, checked and adjusted all the isolastics and engine mounting bolts, wheel alignment, wheels balanced, adjusted hydraulic steering damper trying different settings, tried varying my seating position but difficult with a solo seat. I thought it might have been my jeans legs flapping but its the same wearing leathers (I haven't tried wearing shorts though). The last suspects are the wider American handlebars (I've always preferred the short flat bars) and maybe the fourth rubber mount (Dreer commando). I haven't tried adjusting the preload on the front fork springs but I doubt this would have any effect.
 
edward said:
The thing that's bothered me most since I bought my bike is the sense of instability when travelling at a steady speed, about 70 mph on motorways, it is particularly bad on the M1 as there is a section of road before the Berowra turnoff which has a finely 'ribbed' surface, (possibly a prelude to a resurfacing which has never happened) the front end of the bike feels oversensitive like its about to start a deathweave, there is no problem when accelerating even at much higher speeds on minor roads. I changed from Avons to TT100's (19" front and 18" rear) a narrower tyre on the front, put a Dave Taylor head steady on, checked and adjusted all the isolastics and engine mounting bolts, wheel alignment, wheels balanced, adjusted hydraulic steering damper trying different settings, tried varying my seating position but difficult with a solo seat. I thought it might have been my jeans legs flapping but its the same wearing leathers (I haven't tried wearing shorts though). The last suspects are the wider American handlebars (I've always preferred the short flat bars) and maybe the fourth rubber mount (Dreer commando). I haven't tried adjusting the preload on the front fork springs but I doubt this would have any effect.
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Have you checked the swingarm bushes??
 
phil yates said:
Nater_Potater said:
A quick bit of math shows the trail decreasing about 1/8" for every 1/2" decrease in rear wheel rolling radius. A 1/4" drop of the front forks to increase the trail helped plant the front end of the BSA B50MX when flat-tracking, so I can see where that could be felt at speed on the tarmac.

hobot said:
A real investigator would switch wheels from one MK3 to the other to see what happens to make sense of it.
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Yeah, Phil; listen to Steve! You have the perfect troubleshooting tool in front of you, and yet, you'd rather throw money at it. What's with you, man? I'll PM my Paypal account to you. Send me your extra cash, and I'll get back to you with my findings.

Nathan
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I have learnt in the past, that what you don't spend of your money on Nortons, women will spend it for you on anything BUT Nortons. It is a race to the bottom.

In any case, why bother? I want a 19" rear wheel regardless. Fitting 3.60 front tyres to both bikes will be most interesting. With already knife edge steering, I can imagine how the 3.60 up front will feel. 4.10's removed will become spare rears, no wastage here at Mittagong Norton.

hobot mentions something about too soft a head steady. Nothing up there much adjustable beyond ensuring no slop in bearings. But I guess could be pinched up a tad to see if any difference. So Roadster handles best of the two, but slop in the gear change needs attention as primary case bush appears worn. Roadster clutch action is typical "spring release" in feel whereas Fastback is lighter and more progressive, same with front brake. These variations make for a lot of fun working to equal one with the other. The great thing with having two Commandos is that down time on either does not leave you without a Norton to ride. I couldn't go a week without a ride on a Commando. Life would be miserable indeed. The up and coming super charger project will be a whole new world again and I have already spoken to Jim Comstock about this. Jim is building a strong billet engine and plans to work on an upgraded transmission as well. The result will be very interesting with regards to blowing the engine. The downside will be the requirement to renovate every room in the house. One new Norton equals one new room renovation in the ratio of 1:3 money wise. One super charger equals one whole house, I am told!

Nortons are a very expensive past time. The upgrade addiction is shockingly expensive.

Phil
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try owning a Ferrari. Nortons are cheap in comparison. I was going to suggest swapping the rear wheels over but Steve got in first. Why don't you, because then we will know now rather than later if that is the answer, and the object of this forum is to get answers as well as have fun. BTW my july 71 750 had Avon GP's front and rear. my 850 has a tt100on the front and an avon roadrider on the back. Bit of a cock up I know but don't get the handling problem. I cant be bothered changing tyres till they are worn out. I am lucky to be able to swap rear wheels over on these bikes as well.
 
Fullauto said:
Phil,
It's quite alright to throw money at a Norton. Just make sure that it gets spent wisely. The TT100 tyres are old technology. The pressures you are running are inadequate. I run alloy rims (Morad) in 2.5" x 19" both ends. With 100/90 Avon Roadriders with 34psi rear and 32psi front it has a nice light touch to the steering with absolutely no stability issues as the speed gets higher. This way, when the rear wears out, the front tyre gets fitted to the rear and the new tyre goes on the front. This will make a big difference to your handling. If I had 200 litres of kerosene I wouldn't run it in my Norton "because I already had it".

Jim Comstock's beautiful headsteady is worth the ask. Simple, neat, no adjusting. Simple to fit and does the job. Ikon shocks are the business. Made just down the road from you. Not cheap, but worth the ask.
Click to expand...

Thanks ken
My understanding is that modern TT100's are modern soft compound but 70's tread pattern. I hear what you say re Avon Roadriders and would simply dump the Dunlops if necessary, maybe put them on the car? Or on the boat (don't have one) as wharf buffers. I'm running the same tyres and pressures on the Roadster as the Fastback so feel the high speed stability issue lies somewhere else. If I had 200 litres of kerosene, I'd roast a few Saki- Suckers just for good measure (no abuse please!). :)

I'll discuss the head steady with Jim who should receive my Fullauto within ten days. Thanks for the posting tip re UPS. I thought hobot was talking about the steering head so now see what he was suggesting. But everything should be okay with everything on the bike having been replaced to virtually make it better than new. The 18" alloy rear wheel is going, can't talk me out of that (not that you were). Money spent on a Norton is money invested in a non depreciating motorcycle in my opinion. Unlike my Kawasaki which depreciated to the tune of $5000 in three years. THAT is definitely money lost forever!

Phil
 
edward said:
The thing that's bothered me most since I bought my bike is the sense of instability when travelling at a steady speed, about 70 mph on motorways, it is particularly bad on the M1 as there is a section of road before the Berowra turnoff which has a finely 'ribbed' surface, (possibly a prelude to a resurfacing which has never happened) the front end of the bike feels oversensitive like its about to start a deathweave, there is no problem when accelerating even at much higher speeds on minor roads. I changed from Avons to TT100's (19" front and 18" rear) a narrower tyre on the front, put a Dave Taylor head steady on, checked and adjusted all the isolastics and engine mounting bolts, wheel alignment, wheels balanced, adjusted hydraulic steering damper trying different settings, tried varying my seating position but difficult with a solo seat. I thought it might have been my jeans legs flapping but its the same wearing leathers (I haven't tried wearing shorts though). The last suspects are the wider American handlebars (I've always preferred the short flat bars) and maybe the fourth rubber mount (Dreer commando). I haven't tried adjusting the preload on the front fork springs but I doubt this would have any effect.
Click to expand...

Hmm edward
One common thread between you and me is the 18" rear wheel. I'm sure a lot of Americans will say can't be. I'll find out soon enough.

Phil
 
try owning a Ferrari. Nortons are cheap in comparison. I was going to suggest swapping the rear wheels over but Steve got in first. Why don't you, because then we will know now rather than later if that is the answer, and the object of this forum is to get answers as well as have fun. BTW my july 71 750 had Avon GP's front and rear. my 850 has a tt100on the front and an avon roadrider on the back. Bit of a cock up I know but don't get the handling problem. I cant be bothered changing tyres till they are worn out. I am lucky to be able to swap rear wheels over on these bikes as well.[/quote]




I own three Ferrari's and two Maserati's.

Only joking!!!
I can imagine the service bills on a Ferrari. But if that's what you love and can afford the interest in such, why not? my ex father in law restored warbirds and one we flew together in was a ground attack twin jet. Unbelievable performance, unbelievable fuel consumption. Like go for a fly, then fill er up with $2000 worth of fuel. It was staggering but I didn't pay the bill. Tragically, he killed himself doing what he loved at age 75.

Okay, for you and hobot, I'll swap the rear wheels and report back. I agree it will be interesting. Might also crank up the rear Hagons as suggested by Time. I do listen, just not very often :) Selective hearing!!

Phil
 
Phil, you must be much more sensitive than I am. I crashed a lot of times before I could see it coming. Main problem was drum front brakes, however I rode my Triton for years with exhausting heavy handling after I fitted 18 inch wheels to it to get decent rubber. It is never really that obvious where the problems come from. I just thought the Triton was nice and stable, even though it always ran wide a bit in corners. The Seeley Commando is a much better thing - much easier on the nerves.
 
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