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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: 121445" data-attributes="member: 456"><p>The way that I imagine this is to consider the Armstrong damper as just a short damper when compared with the original Vincent one. If you accept that and the fact that the upper eye is still going to have to fit into the same place at the top then the only way to make the geometry the same as original is to bring up the lower mounting by using extended eyebolts. If you just remove the inner springs then it is true that the front end will sink down but you will almost certainly find that the front end will bottom out frequently. David Dunfey came up with a solution several years ago and that was to use shorter stiffer springs at the front. This gave different pre-load and a shorter stiffer movement. His original suggestion of 75 lbs/inch springs at the front proved too soft for all but the lightest of stripped down racing bikes and he had to design three different spring strengths. I had several sets of these made for people until I met John Emmanuel and understood what he had done. This is a much more sophisticated method that alters the geometry and thus the path of the front wheel movement. I had several copies of John's system made and then realised that it was also possible to alter the comfort and front wheel control by modifying both the front springs and the damper.. It took some more time before I also realised that one has to think about the front suspension in a slightly different way. It does not matter whether it is a single or a twin, the un-sprung weight at the front is the same; forks, wheel, spring boxes, mudguard and stays, headlight etc. It also became clear that weight at the rear, passenger, pannier boxes etc also seems to make very little difference to what is required with the front suspension. It is the weight of the rider, fuel tank, UFM and the engine/gearbox unit which are being controlled and it is a combination of springs and front damper which do this. What really made me understand this is when the 20 stone/127kg test rider changed from Oilite to needle roller bearing at the front and we had to go to a stiffer damper and stiffer springs with less pre-load. The more people who give feedback on their use of the new front end the better I will be able to judge what the best combination of springs and damper will be. For example, over the last couple of days I have been in correspondence with one of our German friends who weighs 17 stones/108 kg and has a Comet. That weight combination suggests either 36lbs/inch springs and a normal AVO damper on its stiffest setting or 45 lbs/inch springs and a stiffer AVO damper on about its lightest setting. It will probably be best that he tries both and then returns whatever he does not use.</p><p></p><p>Finally, Albervin above writes about the steering damper. I went to the trouble of designing a hydraulic one, one model of which fits to the modified steering heads and the other model fits the standard steering head. On a different thread earlier today the use of oil on the rear suspension friction dampers was discussed as friction dampers have certain limitations. Why would anyone stay with a friction damper for the steering when a compact alternative which does not go fore and aft is available?</p></blockquote><p></p>
[QUOTE="timetraveller, post: 121445, member: 456"] The way that I imagine this is to consider the Armstrong damper as just a short damper when compared with the original Vincent one. If you accept that and the fact that the upper eye is still going to have to fit into the same place at the top then the only way to make the geometry the same as original is to bring up the lower mounting by using extended eyebolts. If you just remove the inner springs then it is true that the front end will sink down but you will almost certainly find that the front end will bottom out frequently. David Dunfey came up with a solution several years ago and that was to use shorter stiffer springs at the front. This gave different pre-load and a shorter stiffer movement. His original suggestion of 75 lbs/inch springs at the front proved too soft for all but the lightest of stripped down racing bikes and he had to design three different spring strengths. I had several sets of these made for people until I met John Emmanuel and understood what he had done. This is a much more sophisticated method that alters the geometry and thus the path of the front wheel movement. I had several copies of John's system made and then realised that it was also possible to alter the comfort and front wheel control by modifying both the front springs and the damper.. It took some more time before I also realised that one has to think about the front suspension in a slightly different way. It does not matter whether it is a single or a twin, the un-sprung weight at the front is the same; forks, wheel, spring boxes, mudguard and stays, headlight etc. It also became clear that weight at the rear, passenger, pannier boxes etc also seems to make very little difference to what is required with the front suspension. It is the weight of the rider, fuel tank, UFM and the engine/gearbox unit which are being controlled and it is a combination of springs and front damper which do this. What really made me understand this is when the 20 stone/127kg test rider changed from Oilite to needle roller bearing at the front and we had to go to a stiffer damper and stiffer springs with less pre-load. The more people who give feedback on their use of the new front end the better I will be able to judge what the best combination of springs and damper will be. For example, over the last couple of days I have been in correspondence with one of our German friends who weighs 17 stones/108 kg and has a Comet. That weight combination suggests either 36lbs/inch springs and a normal AVO damper on its stiffest setting or 45 lbs/inch springs and a stiffer AVO damper on about its lightest setting. It will probably be best that he tries both and then returns whatever he does not use. Finally, Albervin above writes about the steering damper. I went to the trouble of designing a hydraulic one, one model of which fits to the modified steering heads and the other model fits the standard steering head. On a different thread earlier today the use of oil on the rear suspension friction dampers was discussed as friction dampers have certain limitations. Why would anyone stay with a friction damper for the steering when a compact alternative which does not go fore and aft is available? [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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