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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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<blockquote data-quote="timetraveller" data-source="post: 75825" data-attributes="member: 456"><p>This is a response to hadronuk #51 above. My memory is that the repair was neither along the line of the road nor at ninety degrees to it but at an angle to a ninety degree line; possible something like 10 or 20 degrees to such a line. However it is a long time ago and I was unconscious for some time.</p><p>With regards to the amount of travel and more being better. The problem is this. Consider the top link only. As the forks lower this tilts down at the front until at some stage the inside of the front of this link touches the shroud of the damper. Removing the shroud would prevent this. Now consider the lower link. As the forks lower this tilts down more and more at the front. Now imagine a curve which is the path of the front of that link. Once it is below the horizontal then that path is starting to curve towards the back of the bike. If it was possible for the link to drop a long way down then any upwards impact on the front wheel, a bump in the road, would not only have to try to move the front of the link upward but also forwards. It seems to me that once the bike is loaded then the bottom link should be as near to horizontal as possible with its front just above the horizontal rather than below it. The question now is whether a longer damper, with more travel, could be combined with springs of such a strength that enough of that travel was used up when the bike was loaded to allow the bottom link to get to its horizontal position. That might mean softer springs or less preload. If the links were longer then this would all be easier but then all sorts of problems with trail would occur and a whole new can of worms would open up. So far as I can tell by playing about with a front end set up on a work bench and clamped so that the base of the oil tank is horizontal we are not going to be able to do much better than the standard length AVO, which limits the downward angle of the lower link to about half an inch lower at the front, and some soft springs, which, when the bike is loaded, allow that link to rise at the front so that it is horizontal. I need the results of tests with different riders with different spring strength to know where an optimum is. For example, it might be that a longer damper with softer springs might still allow the lower link to get to the preferred angle and allow the maximum possible movement of the wheel. This would also include the compression of the bump stop in the damper, which can give an extra half inch of compression in the damper. The springs have to be strong enough to prevent anything bottoming out and as the bikes can be subjected to a range of loads the best that we can do is to find a compromise that suits the largest number of people. At the moment my GUESS is that the 30 lbs/inch springs might be correct for Comets and stripped down racers and the 36 lbs/inch spring correct for the rest of us. If it transpires that softer spring will work on the loaded twins then it might be that the longer damper and softer springs is the correct combination. The upcoming tests will tell us.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 75825, member: 456"] This is a response to hadronuk #51 above. My memory is that the repair was neither along the line of the road nor at ninety degrees to it but at an angle to a ninety degree line; possible something like 10 or 20 degrees to such a line. However it is a long time ago and I was unconscious for some time. With regards to the amount of travel and more being better. The problem is this. Consider the top link only. As the forks lower this tilts down at the front until at some stage the inside of the front of this link touches the shroud of the damper. Removing the shroud would prevent this. Now consider the lower link. As the forks lower this tilts down more and more at the front. Now imagine a curve which is the path of the front of that link. Once it is below the horizontal then that path is starting to curve towards the back of the bike. If it was possible for the link to drop a long way down then any upwards impact on the front wheel, a bump in the road, would not only have to try to move the front of the link upward but also forwards. It seems to me that once the bike is loaded then the bottom link should be as near to horizontal as possible with its front just above the horizontal rather than below it. The question now is whether a longer damper, with more travel, could be combined with springs of such a strength that enough of that travel was used up when the bike was loaded to allow the bottom link to get to its horizontal position. That might mean softer springs or less preload. If the links were longer then this would all be easier but then all sorts of problems with trail would occur and a whole new can of worms would open up. So far as I can tell by playing about with a front end set up on a work bench and clamped so that the base of the oil tank is horizontal we are not going to be able to do much better than the standard length AVO, which limits the downward angle of the lower link to about half an inch lower at the front, and some soft springs, which, when the bike is loaded, allow that link to rise at the front so that it is horizontal. I need the results of tests with different riders with different spring strength to know where an optimum is. For example, it might be that a longer damper with softer springs might still allow the lower link to get to the preferred angle and allow the maximum possible movement of the wheel. This would also include the compression of the bump stop in the damper, which can give an extra half inch of compression in the damper. The springs have to be strong enough to prevent anything bottoming out and as the bikes can be subjected to a range of loads the best that we can do is to find a compromise that suits the largest number of people. At the moment my GUESS is that the 30 lbs/inch springs might be correct for Comets and stripped down racers and the 36 lbs/inch spring correct for the rest of us. If it transpires that softer spring will work on the loaded twins then it might be that the longer damper and softer springs is the correct combination. The upcoming tests will tell us. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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