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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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<blockquote data-quote="davidd" data-source="post: 79231" data-attributes="member: 1177"><p>Chris,</p><p></p><p>I am not sure I am following you, so don't take my lack of understanding as criticism. If I think about fork design in the largest sense possible I would guess that engineers would try and minimize the variables that they are working with. Thus, variables like rigidity, which if low enough can introduce poor steering response, and friction, which, if high enough, could introduce poor suspension compliance would be minimized by the designer. I suspect that the Girdraulic was built with the idea that it was quite rigid and as compliant as possible. It would have been no worse that the bushed Bramptons in terms of compliance, while being much more rigid. That is my guess.</p><p></p><p>I think they would have used materials of the lowest friction possible for the bushings. They did so for the RFM, using a taper roller, and it performs quite well with the same damper. I have the sense that they shied away from roller bearings in the fork because of the number and cost of such an endeavor, rather than the desire to introduce some method of progressive friction damping by using bushes.</p><p></p><p>If I follow the angularity idea, I can see it happening at the extremes, but the fork works within a tiny range. I am not sure that there can be a large variation here. If I visualize the front brake lever, I want it working at 90° where it pulls the best. If it is rotated to point straight down, the force in the bushing becomes huge and the lever does not move when the brake is applied. Of course, the more it is angled from this position, the more the pressure in the bushing is reduced. But, it operates in a small range and not near the extremes. I also think that replacing the bushing in the brake with a needle roller would yield a beneficial reduction in friction that might need to be addressed with a stiffer brake spring to make the application of the brake more progressive. But, most folks would happily trade a bushing for a bearing in the brake with the idea that the external brake spring is a more reliable way to modulate the pull rather than adjusting the friction in the bushing.</p><p></p><p>My racer was very close to ball bearing performance in the front end. I have mentioned that I could bounce it up and down like a basket ball. Most Vincents will not do this and it tends to prove that there is wild variation in the bushed forks. I had no bottoming with the short 75 Lbs. spring in both spring boxes. I could have tuned it a little better, but it worked so well that I moved on to other issues. </p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 79231, member: 1177"] Chris, I am not sure I am following you, so don't take my lack of understanding as criticism. If I think about fork design in the largest sense possible I would guess that engineers would try and minimize the variables that they are working with. Thus, variables like rigidity, which if low enough can introduce poor steering response, and friction, which, if high enough, could introduce poor suspension compliance would be minimized by the designer. I suspect that the Girdraulic was built with the idea that it was quite rigid and as compliant as possible. It would have been no worse that the bushed Bramptons in terms of compliance, while being much more rigid. That is my guess. I think they would have used materials of the lowest friction possible for the bushings. They did so for the RFM, using a taper roller, and it performs quite well with the same damper. I have the sense that they shied away from roller bearings in the fork because of the number and cost of such an endeavor, rather than the desire to introduce some method of progressive friction damping by using bushes. If I follow the angularity idea, I can see it happening at the extremes, but the fork works within a tiny range. I am not sure that there can be a large variation here. If I visualize the front brake lever, I want it working at 90° where it pulls the best. If it is rotated to point straight down, the force in the bushing becomes huge and the lever does not move when the brake is applied. Of course, the more it is angled from this position, the more the pressure in the bushing is reduced. But, it operates in a small range and not near the extremes. I also think that replacing the bushing in the brake with a needle roller would yield a beneficial reduction in friction that might need to be addressed with a stiffer brake spring to make the application of the brake more progressive. But, most folks would happily trade a bushing for a bearing in the brake with the idea that the external brake spring is a more reliable way to modulate the pull rather than adjusting the friction in the bushing. My racer was very close to ball bearing performance in the front end. I have mentioned that I could bounce it up and down like a basket ball. Most Vincents will not do this and it tends to prove that there is wild variation in the bushed forks. I had no bottoming with the short 75 Lbs. spring in both spring boxes. I could have tuned it a little better, but it worked so well that I moved on to other issues. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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