Suspension - please explain.
- Thread starter Howard
- Start date
Thanks Bruce, But I thought Howard wanted to do a quickie job with the standard setup,
Like I was thinking, Or have I got it wrong again ?.
Like I was thinking, Or have I got it wrong again ?.
You're right Bill, not so much "a quickie job" but I am trying to keep it looking fairly original, hence the rear suspension mods, instead of Avo which I'm sure would be better, and it's a project to keep my brain and hands working rather than bolt on goodies without much thought - it also gives the Forum a topic, so win, win.
Howard, if you want to keep the standard geometry and just replace the Oilites with a freer type of bearing then you have to consider why this type of mod was developed. Both John Emmanuel and Dave Dunfey came to the same conclusion in that the front wheel path with the standard Vincent set up could cause trouble. They independently arrived at different methods of changing this path. The suspicion is that the problem was known to Vincents early on as when one looks at photographs of work racing bikes from the early 1950s they all have the bottom link horizontal. That limits which part of the original wheel spindle track is used. It should also be noted that George Brown was also not happy with the front end and when he built Nero he changed to telescopic forks. David's first attempt at a cure was to use shorter, stiffer springs at the front which put the wheel path back to what the works racers were using. John's efforts were more adventurous in that he realised that he wanted a different wheel path and he then set up a jig to replace the lower support for the steering head and rear pivot point for the lower link and then moved the pivot point about until he had the wheel movement that he thought would be better. He wanted to, as nearly as possible, make the front wheel movement similar to that given by telescopic forks, i.e. upwards and backwards. To understand fully what is wrong with the original system one needs to study the wheel path, which is like a distorted 's'. To finally drive it home borrow an enclosed 'D' and then brake hard, or use a disc brake, and see what happens. The whole of the 'dashboard' rises up to meet one as the brake is applied. This means that the front suspension has dropped to its lowest level, the wheel has moved backwards and the trail has increased to about 5". One has to release the front brake before the wheel can move forwards again and the suspension starts to work.
Just replacing the Oilites with, say, ball races, will reduce the friction but will do nothing to change the wheel path. Indeed, I would expect that one might run into serious trouble as one would then have the original wheel path and much freer movement. The original dampers would not be up to controlling that movement in my opinion. Please remember that when Chris Launders changed his Oilites for needle rollers there was so much movement that we thought that the new AVO damper had failed.
So, by all means replace the Oilites with bearings and all the other bushes with needle rollers if you wish but do not blame me if you and the bike end up in a ditch somewhere.
The use of a hydraulic steering damper is not because the new system is more likely to cause a speed wobble than the original one. Quite the contrary in fact. However, it is worth asking a question and please understand that I am not 'getting at' anyone who prefers to stay with friction damping. The question is why do you not see any modern bikes or cars using friction dampers on their suspension or steering? It is clearly not a matter of cost but of function. We all know, and have known since we were children that friction damping gives lots of 'sticktion' and very little damping. You will also not find many/any modern machines which use the same amount of damping in compression as extension. There is a reason for that. When I decided to design a hydraulic steering damper system to fit to either the modified or original systems it was because I have been in a speed wobble at 100 mph and it is not a good experience. I landed on my face and my goggles went through their backing and took a piece of from my cheek bone right down to near my jaw line. I was not beautiful before but sure as h**l I was less beautiful afterwards.
Now to Bill's comments. Replacing the eccentrics with concentrics will not do the job. I have tried to explain that it is not the use of concentrics which is important but the centre of rotation of the rear of the lower link. This is moved by far more than the difference between an eccentric and a concentric and you could well end up making things worse rather than better. Please do not do it.
Here endeth the lesson.
Just replacing the Oilites with, say, ball races, will reduce the friction but will do nothing to change the wheel path. Indeed, I would expect that one might run into serious trouble as one would then have the original wheel path and much freer movement. The original dampers would not be up to controlling that movement in my opinion. Please remember that when Chris Launders changed his Oilites for needle rollers there was so much movement that we thought that the new AVO damper had failed.
So, by all means replace the Oilites with bearings and all the other bushes with needle rollers if you wish but do not blame me if you and the bike end up in a ditch somewhere.
The use of a hydraulic steering damper is not because the new system is more likely to cause a speed wobble than the original one. Quite the contrary in fact. However, it is worth asking a question and please understand that I am not 'getting at' anyone who prefers to stay with friction damping. The question is why do you not see any modern bikes or cars using friction dampers on their suspension or steering? It is clearly not a matter of cost but of function. We all know, and have known since we were children that friction damping gives lots of 'sticktion' and very little damping. You will also not find many/any modern machines which use the same amount of damping in compression as extension. There is a reason for that. When I decided to design a hydraulic steering damper system to fit to either the modified or original systems it was because I have been in a speed wobble at 100 mph and it is not a good experience. I landed on my face and my goggles went through their backing and took a piece of from my cheek bone right down to near my jaw line. I was not beautiful before but sure as h**l I was less beautiful afterwards.
Now to Bill's comments. Replacing the eccentrics with concentrics will not do the job. I have tried to explain that it is not the use of concentrics which is important but the centre of rotation of the rear of the lower link. This is moved by far more than the difference between an eccentric and a concentric and you could well end up making things worse rather than better. Please do not do it.
Here endeth the lesson.
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Thanks Norman, I am aware of your points. I'll read it again later - until I fully understand - and consider next steps. When I've ridden it a bit, it may be that the Girdraulics are as good as they've ever been, but now the rear is more comfortable they show up as the next part in need of update - this can go on forever if I don't decide when enough is enough.
I was only thinking of making our Comet forks work a bit more fluid.
Mine are not too bad, I have Normans/Davidd short springs , Plus a Bit !!.
My Twin works a bit better, I think because of the extra weight.
I even put a bit of valve spring inside the standard damper to give it a bit of rebound !!,
There is No hope for me !.
They say this ZX1 lube is very slippy, If I can find a shop that sells it, I think it's worth a try.
Mine are not too bad, I have Normans/Davidd short springs , Plus a Bit !!.
My Twin works a bit better, I think because of the extra weight.
I even put a bit of valve spring inside the standard damper to give it a bit of rebound !!,
There is No hope for me !.
They say this ZX1 lube is very slippy, If I can find a shop that sells it, I think it's worth a try.
Bill, ZX1 grease for sale.
https://www.ebay.co.uk/itm/ZX1-Extr...005320&hash=item3b459138bd:g:9NYAAOSwwKxbsgAu
I've put my now patented suspension sensors (cable ties) on the front damper and spring boxes to get an idea of how much and where the travel is, but the forks seem to be free and moving as intended.
https://www.ebay.co.uk/itm/ZX1-Extr...005320&hash=item3b459138bd:g:9NYAAOSwwKxbsgAu
I've put my now patented suspension sensors (cable ties) on the front damper and spring boxes to get an idea of how much and where the travel is, but the forks seem to be free and moving as intended.
Howard,
It sounds like you have had great success with the rear suspension. Fortunately, the rear suspension has a lot of movement. The front does not. It is not easy to get a full range of comfortable spring in 3" of travel. Most bikes need somewhere between 600-700 lbs. to resist bottoming out when the front brake is grabbed when two-up and at speed. At the same time, we want the springs to be light enough to absorb ripples in the pavement. It is a tall task.
As far as I know, the best front suspension set-up is the coil-over. When Carleton Palmer installed his he said that the "harshness went away." I suspect this is due to the differing motion ratios of the spring box vs. the coil-over, but I am not certain. David Tompkins noted the improvement to the handling of his racer at Laguna Seca with the coil-over and the Reg Bolton type modification.
Just for information, Ertalyte TX is a good bearing plastic that is oil-impregnated
David
It sounds like you have had great success with the rear suspension. Fortunately, the rear suspension has a lot of movement. The front does not. It is not easy to get a full range of comfortable spring in 3" of travel. Most bikes need somewhere between 600-700 lbs. to resist bottoming out when the front brake is grabbed when two-up and at speed. At the same time, we want the springs to be light enough to absorb ripples in the pavement. It is a tall task.
As far as I know, the best front suspension set-up is the coil-over. When Carleton Palmer installed his he said that the "harshness went away." I suspect this is due to the differing motion ratios of the spring box vs. the coil-over, but I am not certain. David Tompkins noted the improvement to the handling of his racer at Laguna Seca with the coil-over and the Reg Bolton type modification.
Just for information, Ertalyte TX is a good bearing plastic that is oil-impregnated
David
I know coil over damper is the way to go, I suspect removing the spring boxes has a good effect. My early 80s race Comet used a standard Vin damper threaded on the outside to locate/adjust a coil spring. That seemed to work well, but I'm just trying to get the best out of what I've got - the Comet was perfectly ok for its current use, but if I can burn off some of this lockdown time learning how it all works and saving my old bones some pain that would be good too.
David, Look at photo of Howard in post 19,
He was years ahead of us, I thought it was 70s, But I have lost the plot !!.
But I knew the Bike before Howard had it. Cheers Bill.
He was years ahead of us, I thought it was 70s, But I have lost the plot !!.
But I knew the Bike before Howard had it. Cheers Bill.