Commando suspension setup

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Lowering the front end will tend to reduce the amount of trail you have, but it will also reduce the ground clearance and greatly increase the chances of crashing so its not that good an idea really. To improve handling on any bike with 1960s type geometry, steepening the steering angle by around 2.5 degrees will work very well indeed, and transform the slow sluggish steering provided by chopper type geometry.
 
Carbonfibre said:
steepening the steering angle by around 2.5 degrees will work very well indeed, and transform the slow sluggish steering provided by chopper type geometry.
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Nortons INCREASED the steering angle on the 850 by a degree, reputedly to take the twitchiness and tendency to a high speed weave out of it.

Anyone still alive here that has tried decreasing the steering angle, like Carbonfibre suggests ?? Perhaps we should ask Carbonfibre if he has actually tried it on a Norton ???

P.S. went on a testride of an old rocketship a while back, the sales guy warned me of the 'slow steering'' (it was an old model), that thing could do loops around a shopping trolley....
 
What people dont seem to grasp is that the very poor tyres and suspension that were common in the 1970s dictated to some extent the need for chopper type steering geometry. Today far better alternatives are easily available, which means a small adjustment to the steering angle of a 60s type machine, will mean greatly improved handling for a very reasonable cost.
 
Yes but have you actually tried this, or is this airy-fairy stuff ?

Just changing the fork angle is not exactly a complete suspension redesign to modern dimensions, and unless you do something really radical its still going to have the same type tyres/sizes.

Some bikes that have appeared here have had upside-downies fitted (modern upside down forks), be interesting to hear what angles they were fitted to, and how they behave. ??
And if they have been tried seriously at speed anywhere....

Anyone know the steering angle of the 961 ?
 
I would not have a problem with changing the angle on any chopper type frame, but not completely sure on the Commando as the rubber mounted rear wheel is something that might mean changes which would work perfectly on almost anything else might not work on this frame?

Modern forks should work very well indeed over the 1950s Norton OE parts, as they are far more rigid and less likely to twist and have far more sophisticated damper systems, which can be easily adjusted to suit specific applications perfectly.

I would guess that a Norton fitted with modern suspension, and a properly designed method of limiting isolastic movement to acceptable level, would handle very well, but suspension which works well is not simply a matter of bolting on replacement parts, and ideally the component parts need to be made or adjusted specifically to suit each particular application.
 
So can we sign you up for a new 961 ?

We still don't know your ride....
 
Carbonfibre said:
Can anyone actually get hold of a 961 for real rather than just paying a deposit?
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There seems to be quite a few on the road in the UK now-although I haven't seen one yet-but then I don't go to Norton Owners Club gatherings.
They occasionally turn up on UK ebay so you don't necessarily even have to pay a deposit and wait.
 
You sure can!
As my damper rods are tubes, rebound pressure is forced up past the 5mm needle to the top nut area, i have a modified nut that so a a oil pressure gauge can be attached,and if i could post pictures i would send one!
Anyway thats how i know, the original norton damper rod was replaced with a tube that did the same job. the first pressure test reading was 45 psi . But the damper was used and proberly worn, the Lansdowne Damper ruined a 200 psi gauge,the needle went right round back to the start and bent the needle :!: then returned to the 50 psi position.

350 psi sounds a lot, but remember the dimensions , tube bore 20mm, rod dia 10mm , so 314.159 -78.5398 = 236 square mm .so 350 psi divided by 23.6 % = 83 lbs of upward resisttance...but you already knew that. and i aint that strong to up-ward pull 350 lb :!:
Best Regards
http://www.lansdowne-engineering.com
 
john robert bould said:
You sure can!
As my damper rods are tubes, rebound pressure is forced up past the 5mm needle to the top nut area, i have a modified nut that so a a oil pressure gauge can be attached,and if i could post pictures i would send one!
Anyway thats how i know, the original norton damper rod was replaced with a tube that did the same job. the first pressure test reading was 45 psi . But the damper was used and proberly worn, the Lansdowne Damper ruined a 200 psi gauge,the needle went right round back to the start and bent the needle :!: then returned to the 50 psi position.

350 psi sounds a lot, but remember the dimensions , tube bore 20mm, rod dia 10mm , so 314.159 -78.5398 = 236 square mm .so 350 psi divided by 23.6 % = 83 lbs of upward resisttance...but you already knew that. and i aint that strong to up-ward pull 350 lb :!:
Best Regards
http://www.lansdowne-engineering.com
Click to expand...
YIKES!
Is this why I seem to seep a bit on the compression side. 350psi, for christmas sakes what sort of pressures are the sliders rated at or for that matter, stock seals?
 
pvisseriii said:
YIKES!
Is this why I seem to seep a bit on the compression side. 350psi, for christmas sakes what sort of pressures are the sliders rated at or for that matter, stock seals?
Click to expand...

But what John is describing is the pressure inside the damper tube not the actual fork leg.
 
Carbonfibre said:
Lowering the front end will tend to reduce the amount of trail you have, but it will also reduce the ground clearance and greatly increase the chances of crashing so its not that good an idea really. To improve handling on any bike with 1960s type geometry, steepening the steering angle by around 2.5 degrees will work very well indeed, and transform the slow sluggish steering provided by chopper type geometry.
Click to expand...

Then you would end up with a very twitchy bike with some 20% less trail than a 'modern' bike, try it and get back to us
 
A race builder told me they tired a degree or so reduced trail and it pitched the pilot off in a turn for bad injury. I've tried the 850 rake on and off road and it felt sluggish on pavement and resistive off road to me. Got back on Combat 750 and immediately was comfy to hot dog it around the pasture/trees and easy cornering on stable road surface. Maybe just me but thats who I must ride with. ugh.

I find I like a soft rear end to ride hard. Will try the 80-120 long springs unloaded but Peel has gas shocks on so might be able to diddle it up on way home with 4 cases of beer.
 
Cheesy said:
Carbonfibre said:
Lowering the front end will tend to reduce the amount of trail you have, but it will also reduce the ground clearance and greatly increase the chances of crashing so its not that good an idea really. To improve handling on any bike with 1960s type geometry, steepening the steering angle by around 2.5 degrees will work very well indeed, and transform the slow sluggish steering provided by chopper type geometry.
Click to expand...

Then you would end up with a very twitchy bike with some 20% less trail than a 'modern' bike, try it and get back to us
Click to expand...


If you have a Norton with the same head angle as a modern bike, and alter the angle 2.5 degrees then the trail certainly is going to be less. From blueprints of the frames I have seen it looks to me the Norton has around about a 28 degree angle, while most modern bikes are around 24, so maybe yours has been in an accident at some time?
 
Carbonfibre.
I cannot see any 40 year old norton not being in a crash at some time :!: I think i dropped my Bsa Roadrocket 4 times, old Avon Deathmasters [we called them} with there square block treads where not the best tyres, I suppose being eighteen didn't help also. :D
I have a LR Fast back with a bent top tube, about an Inch down the length, and a slight kink in one downe tube.I know they left the factory with a small bend due to welding,according to Les at fairspares 1/8 is normal.
 
You are certainly right, which means a fair few Commando frames have got steering angles which are a bit steeper than stock, and should mean improved handling.
 
Carbonfibre said:
Cheesy said:
Carbonfibre said:
Lowering the front end will tend to reduce the amount of trail you have, but it will also reduce the ground clearance and greatly increase the chances of crashing so its not that good an idea really. To improve handling on any bike with 1960s type geometry, steepening the steering angle by around 2.5 degrees will work very well indeed, and transform the slow sluggish steering provided by chopper type geometry.
Click to expand...

Then you would end up with a very twitchy bike with some 20% less trail than a 'modern' bike, try it and get back to us
Click to expand...


If you have a Norton with the same head angle as a modern bike, and alter the angle 2.5 degrees then the trail certainly is going to be less. From blueprints of the frames I have seen it looks to me the Norton has around about a 28 degree angle, while most modern bikes are around 24, so maybe yours has been in an accident at some time?
Click to expand...

Where did I say I had a Commando with the same angle as a modern bike?? It doesnt matter what angle you start with if you take off 2.5deg then the trail will drop, in the case of a 750 it will be a reduction of 10-15mm
 
Cheesy ‚ your original question was about the sag and tyre and wheel sizes that people run (so that trail can be calculated).

If you read some other posts on this subject, many Commando owners set great store by 19 inch wheels front and rear and 100/90 tyres front and rear. Some owners prefer a 90/90 on the front, but the consensus seems to be that street Commandos steer better with narrow tyres. Avon Roadriders seem to be the most popular brand and they transformed the steering and straight-line stability on my machine.

I think Norton got the chassis geometry pretty well spot on for a street bike that has to cope with a wide variety of road conditions, and it's still good today. My 850 could carve a nice, tight turn and yet was stable on fast. bumpy roads.

May I ask you why you want to calculate the trail?
 
daveh said:
Cheesy ‚ your original question was about the sag and tyre and wheel sizes that people run (so that trail can be calculated).

If you read some other posts on this subject, many Commando owners set great store by 19 inch wheels front and rear and 100/90 tyres front and rear. Some owners prefer a 90/90 on the front, but the consensus seems to be that street Commandos steer better with narrow tyres. Avon Roadriders seem to be the most popular brand and they transformed the steering and straight-line stability on my machine.

I think Norton got the chassis geometry pretty well spot on for a street bike that has to cope with a wide variety of road conditions, and it's still good today. My 850 could carve a nice, tight turn and yet was stable on fast. bumpy roads.

May I ask you why you want to calculate the trail?
Click to expand...

Pretty much to figure out if a set of USD forks I have will work on a Commando, and if not if I can get the numbers back to where they should be by altering sag and or wheel/tyre size, unfortunately the large offset in the Commando clamps means that it is almost impossible to bring the trail figure back to 100mm +- with the Cerianis and clamps that I have. This leaves a couple of options such as machining the clamps and putting inserts in to alter the offset (or make new clamps which is probably a better idea since the ones I have are magnesium), or making up some inserts for the steering head to reduce the rake, or finding a disc brake slider and using the roadholders (mine is a drum) and playing with them.

Then on top of that I havent had much to do with road going bikes so I wanted to get a feel for how people were setting them up, I know my Husaberg is quite sensitive to sag in the rear and runs quite a bit less than most other bikes of the era (85mm for the Berg as opposed to 100 ish) other wise it doesnt go around corners unless you are some Scandinavian giant who can throw it around like a pit bike....
 
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