Brough suspension looks almost identical to BMW K1200/1300 system to me.
FF: Forks Modified Steering Stem
- Thread starter greg brillus
- Start date
Hello Bill, How good are they, Do they have an Hydraulic Damper ?, Can't see me buying one to find out !!, Not on my Pension, But you never know ??, My early K100 needed one, I would not go over 100 mph with it. Cheers Bill.
Did anyone find my attempted analysis of the forces in the forks of interest? Did anyone spot the deliberate mistake in the slope of the down-force line?
I am hoping to contribute to moving the debate forward. Reading back over the last 50+ years of Girdraulic debates in MPH, it has always followed the same pattern of a number of mainly plausible but untestable theories being aired, then the debate peters out without reaching any conclusions.
The recent spring and modified geometry trials seem promising, so it seems opportune to discuss whether these can inform an attempt to explain as scientifically as possible what is going on. We might be able to then come up with further possible changes to try?
As my original post contains a mistake and was not very legible, I was thinking of redoing it.
I should add that of course the chart of the opposing forces would be far more useful if I was able to put numbers to it. But even if we lack this quantitative analysis, a qualitative understanding of the effects of the forces could still be very useful.
I would much prefer to do this after comments so I can address anything else that seems wrong or unclear. Any thoughts chaps, even if just to say it’s gobbledygook!
I am hoping to contribute to moving the debate forward. Reading back over the last 50+ years of Girdraulic debates in MPH, it has always followed the same pattern of a number of mainly plausible but untestable theories being aired, then the debate peters out without reaching any conclusions.
The recent spring and modified geometry trials seem promising, so it seems opportune to discuss whether these can inform an attempt to explain as scientifically as possible what is going on. We might be able to then come up with further possible changes to try?
As my original post contains a mistake and was not very legible, I was thinking of redoing it.
I should add that of course the chart of the opposing forces would be far more useful if I was able to put numbers to it. But even if we lack this quantitative analysis, a qualitative understanding of the effects of the forces could still be very useful.
I would much prefer to do this after comments so I can address anything else that seems wrong or unclear. Any thoughts chaps, even if just to say it’s gobbledygook!
Sorry Rob, I can't understand those charts and things, I should have gone to school !, I am happy that I know what is wrong, Trouble is nobody agrees !!.
It's wheel balance/bad tryes, Lack of trail + too much weight forward of the steering head.
The cure is fitting norton Forks, I did it in 1975, With lots of lovely TRAIL !!.
The funny thing is you can get away with it for years.
I would be interested in your springs, But I don't understand, I have tried to read your stuff, But I am too thick !.
Good Luck, bill.
It's wheel balance/bad tryes, Lack of trail + too much weight forward of the steering head.
The cure is fitting norton Forks, I did it in 1975, With lots of lovely TRAIL !!.
The funny thing is you can get away with it for years.
I would be interested in your springs, But I don't understand, I have tried to read your stuff, But I am too thick !.
Good Luck, bill.
George Brown used ajs 7r forks and brake, I guess that should tell you something.
Rob, I did spend some time looking at your graph and I am used to looking at graphs professionally so it should not have produced any uncertainty.. However, it did and that might well be my fault. What I wondered was whether this was applicable to the new geometry. One of the axes is 'upwards force' but what we are trying to do is to get rid of the upwards force that occurs with the standard geometry. Now, if I have misunderstood that I apologise but if the upwards force is due to something other than the geometry I need to have it explained to me.
On a different matter and to keep others up to date, the springs have been sent to chrislaun and another batch of springs should be collected tomorrow for Greg Brillus in Australia.. Once these chaps have had time to try them out, and if necessary change them about a bit, then we should be able to home in on the correct combination of spring rate and length and then start and send these out to those who are waiting. I am expecting that different springs will be needed for Comets and twins to get the optimum combination of comfort and handling. Once that is sorted out then if Rob can come up with some suggested improvements I would be happy to see if they can be produced. However, I am expecting that rider's 'seat of the pants' feelings will have the most influence on the final design.
On a different matter and to keep others up to date, the springs have been sent to chrislaun and another batch of springs should be collected tomorrow for Greg Brillus in Australia.. Once these chaps have had time to try them out, and if necessary change them about a bit, then we should be able to home in on the correct combination of spring rate and length and then start and send these out to those who are waiting. I am expecting that different springs will be needed for Comets and twins to get the optimum combination of comfort and handling. Once that is sorted out then if Rob can come up with some suggested improvements I would be happy to see if they can be produced. However, I am expecting that rider's 'seat of the pants' feelings will have the most influence on the final design.
Well I for certain am interested in improvements, but I think what is happening regarding Rob's comments is exactly what I would expect. It is this "Gray Area" regarding suspension where most get lost, as the general public or motorcyclist in our case, have no real idea what is going on. To change a set of springs or a shock absorber seems a reasonable thing, and most can and would carry out this change for an improvement, but beyond that.......You are entering an area that most would not go to. The change thus far regarding the Modified stem works very well, as it allows the font end to perform more like telescopic forks. It appears from the comments of others on this forum, that this is what was needed. I understood that most all owners of Brampton equipped bikes were very happy with their bikes, with no abnormal behavior or head shakes, only that they wish a decent shock absorber could be fitted. Also that we don't really want to change the look of the bikes too much, after all it is a Vincent and not some hybrid that all these crazy owners have concocted. Otherwise all our bikes start looking like something that they are not. When I built the racer, I was very worried about the bad handling characteristics of Girdraulic forks, I had talked to many people including myself who had suffered tank slappers, some who ended up in hospital with very bad injuries, and I had seen the video footage of John Surtees crash on his twin racer. Because I was very keen to use the bike as a true Vincent I wanted to make sure I reduced the problem as much as I could. I would be interested to know what tests you can perform, and what changes or alterations could be made to improve the fork action. I feel that what has been done is enough, though it is possible that fine tuning will help, but the fork action on all three bikes known to me behave completely different to stock Girdraulics. It is really only the few that will install this kit, or carry out a similar mod, that will experience what I am describing. If I could step back in time and could have shown the two Phil's the benefit of this, and if the change had been implemented, I'm sure the Vincent marque would not have received the "Bad Handling" title that it received.
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On the force analysis I wondered for one thing how the "weight transfer under braking" was estimated. If the front doesn't dive, but rises during braking, does that really happen as much it would on a tele equipped bike or with the new geometry? That could probably be measured with a force gauge somewhere up front on the forks. I'm afraid I would need a lot of explanation to get what was represented in the chart.
Testing can only help so much, just like a rolling road will give you some idea how much power your engine is producing, but it wont tell you how to improve it. Vincent forks work fine so long as the geometry allows it to, but in a stock bike, the geometry allows the forks to hang lower than they should, obviously to increase travel. This is really where the problem lies.