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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: 75807" data-attributes="member: 1177"><p>It is still a good question. The short springs I came up with were a quick work around for the wobble problem. But, the wobble problem is really a braking problem also: with a large amount of pre load on the springs the braking and the up and down motion of the Girdraulic forks is linked. This linking is not safe. It is something that if known, any good engineer would re design the system. It was most obvious when racing and also with the advent of disc brake conversions. However, I would argue that this problem has caused many street accidents, so many, in fact, that the Vincent has become rather infamous for its propensity to wobble. The Egli and Norvin seem to be obvious attempts at a complicated work around.</p><p></p><p>If changing the pre load to zero could keep the the forks going up and down during braking, I thought that changing the axle path could do the same. I found on my wood mock-up that moving the eccentric spindle lower did exactly that, severing the up and down motion from the brakes, meaning that the Girdraulic forks no longer seized while the front brakes were applied. </p><p></p><p>As I saw it, the modified stem puts the Girdraulic back to a proper design. This means that the first work around, the short springs with no pre load, could be changed back to springs with pre load when paired with the modified stem. This would be (and is) a great benefit because you can then use all the travel of the Girdraulic without fear of wobbles in order to get the best ride not just the small portion of travel provided by the short springs. This is the tuning that is happening now. I think of the choice of eccentric or concentric to be part of that tuning also.</p><p></p><p>I do think that one or the other of these mods, short springs or new stem, helps you avoid the possibility of bad handling that can cause an accident. You can ride without incident on the stock Vincent for long periods of time and maybe forever. However, knowing that the stock system is potentially dangerous can be a stopper for some of us. Wobbles are always a surprise and unexpected. This mod goes a long way to increasing that often untapped stability that should be on reserve in a properly engineered system.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 75807, member: 1177"] It is still a good question. The short springs I came up with were a quick work around for the wobble problem. But, the wobble problem is really a braking problem also: with a large amount of pre load on the springs the braking and the up and down motion of the Girdraulic forks is linked. This linking is not safe. It is something that if known, any good engineer would re design the system. It was most obvious when racing and also with the advent of disc brake conversions. However, I would argue that this problem has caused many street accidents, so many, in fact, that the Vincent has become rather infamous for its propensity to wobble. The Egli and Norvin seem to be obvious attempts at a complicated work around. If changing the pre load to zero could keep the the forks going up and down during braking, I thought that changing the axle path could do the same. I found on my wood mock-up that moving the eccentric spindle lower did exactly that, severing the up and down motion from the brakes, meaning that the Girdraulic forks no longer seized while the front brakes were applied. As I saw it, the modified stem puts the Girdraulic back to a proper design. This means that the first work around, the short springs with no pre load, could be changed back to springs with pre load when paired with the modified stem. This would be (and is) a great benefit because you can then use all the travel of the Girdraulic without fear of wobbles in order to get the best ride not just the small portion of travel provided by the short springs. This is the tuning that is happening now. I think of the choice of eccentric or concentric to be part of that tuning also. I do think that one or the other of these mods, short springs or new stem, helps you avoid the possibility of bad handling that can cause an accident. You can ride without incident on the stock Vincent for long periods of time and maybe forever. However, knowing that the stock system is potentially dangerous can be a stopper for some of us. Wobbles are always a surprise and unexpected. This mod goes a long way to increasing that often untapped stability that should be on reserve in a properly engineered system. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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