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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: 77936" data-attributes="member: 456"><p>Perhaps I can help with this. Chris has given you all the details that you need for standard Vincent springs and the two 36 lbs/inch springs whish I specified. In the same context as those 36 lb springs there has also been mentioned 30 lbs/inch springs, once again with the same length, pre-load etc. as the 36 lb springs to try out with the new steering heads. These springs were used on a twin race bike used last year at Goodwood and other places and seemed to work correctly. I was hoping that they would also prove suitable for use on road going singles as they are lighter, but just in case I have had some 33 lbs/inch springs made, with the same length etc. to be used on road going singles. These have yet to be tried out.</p><p> So now you know about standard Vincent springs and the ones which are being trialled with the new steering heads. You now need information on yet another batch of springs and these were the brain child of David Dunfey. David had already realised that there was a problem with the standard front geometry and some years ago came up with a solution. This required the use of shorter, but stiffer, front springs. David specified 75 lbs/inch for Comets, 95 (from memory) for twins and 130 (from memory) for sidecar outfits. [Check those values by reading earlier MPHs]. It turned out that the 75s were too weak for road going singles and various combinations of the three spring strengths were used and tested by various people until a satisfactory strength was found. Eventually it transpired that the ones intended for twins were about right for Singles and a combination of Comet and sidecar springs were about right for road going twins. That combination resulted in a combined strength of 102.5 lbs/inch springs was about right and in the end I had some 102 lbs/inch springs made and sent to people. The idea behind these shorter but stiffer springs was to tilt the lower link up at the front so that the wheel only ever moved upwards and backwards rather than upwards, forwards and then backwards which is what happens with the standard geometry. This would result in less movement on the front forks but the wheel spindle path would now be what was wanted. John Emmanuel had also realised that the front geometry needed to be changed and he came up with a different but more expensive solution. It should also be mentioned that John Renwick had also changed the front geometry for his race prepared bikes and he did this by drilling another hole in the girdraulic blades above the original one for the lower link. Most people are not going to want to do that. So that is whey you read of several different springs. In the context of the new steering heads you should be able to forget about the original Vincent ones and David's short but stiff ones. Testing is taking place as quickly as it can be and people will have to wait until there is a consensus as to what works best for most people. I had thought that we had cracked it with the new AVOs and the 36 lbs springs, and possible we have, but the reduction in friction with Greg's modification has to be worked through and in the mean time we can get on with making all the other parts other than the springs.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 77936, member: 456"] Perhaps I can help with this. Chris has given you all the details that you need for standard Vincent springs and the two 36 lbs/inch springs whish I specified. In the same context as those 36 lb springs there has also been mentioned 30 lbs/inch springs, once again with the same length, pre-load etc. as the 36 lb springs to try out with the new steering heads. These springs were used on a twin race bike used last year at Goodwood and other places and seemed to work correctly. I was hoping that they would also prove suitable for use on road going singles as they are lighter, but just in case I have had some 33 lbs/inch springs made, with the same length etc. to be used on road going singles. These have yet to be tried out. So now you know about standard Vincent springs and the ones which are being trialled with the new steering heads. You now need information on yet another batch of springs and these were the brain child of David Dunfey. David had already realised that there was a problem with the standard front geometry and some years ago came up with a solution. This required the use of shorter, but stiffer, front springs. David specified 75 lbs/inch for Comets, 95 (from memory) for twins and 130 (from memory) for sidecar outfits. [Check those values by reading earlier MPHs]. It turned out that the 75s were too weak for road going singles and various combinations of the three spring strengths were used and tested by various people until a satisfactory strength was found. Eventually it transpired that the ones intended for twins were about right for Singles and a combination of Comet and sidecar springs were about right for road going twins. That combination resulted in a combined strength of 102.5 lbs/inch springs was about right and in the end I had some 102 lbs/inch springs made and sent to people. The idea behind these shorter but stiffer springs was to tilt the lower link up at the front so that the wheel only ever moved upwards and backwards rather than upwards, forwards and then backwards which is what happens with the standard geometry. This would result in less movement on the front forks but the wheel spindle path would now be what was wanted. John Emmanuel had also realised that the front geometry needed to be changed and he came up with a different but more expensive solution. It should also be mentioned that John Renwick had also changed the front geometry for his race prepared bikes and he did this by drilling another hole in the girdraulic blades above the original one for the lower link. Most people are not going to want to do that. So that is whey you read of several different springs. In the context of the new steering heads you should be able to forget about the original Vincent ones and David's short but stiff ones. Testing is taking place as quickly as it can be and people will have to wait until there is a consensus as to what works best for most people. I had thought that we had cracked it with the new AVOs and the 36 lbs springs, and possible we have, but the reduction in friction with Greg's modification has to be worked through and in the mean time we can get on with making all the other parts other than the springs. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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