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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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<blockquote data-quote="hadronuk" data-source="post: 75698" data-attributes="member: 1866"><p>I had to replace my spring cases as one could not be straightened sufficiently. On the test rig, the badly bent one was only producing an extra 4 - 6lbs of friction, but that was enough to give a very poor ride over smoother roads, as the forks remained stuck until a larger bump was encountered. The replacement cases from VOC Spares have a plastic lining in the larger diameter part of the outer case. These new cases in a test rig measured exactly the same as my less bent but very old and internally pitted case pair. Ride over smooth roads was much better, rough roads felt much the same. So I conclude that friction in the spring cases has a big impact on damping and comfort over smooth roads, but perhaps much less influence over rough roads. Secondly the plastic lining may be good for reducing wear, but not friction. So provided your old cases are straight, clean and well greased, there may be no functional benefit from replacing them. (Plus the dimensions of the new cases were wrong, resulting in too high a ride height. I did report this, it may be fixed now.)</p><p>There is one other possible spring case problem. Some replacement springs were right on the top tolerance for diameter. This means that as they compress, expand and buckle they can jam in the cases. My suggestion that the original spring specification was wrong received a very frosty response from one very senior and knowledgable club member, but nervertheless, I believe a new batch of springs was made.</p><p></p><p>It is probably extremely arrogant of me to say this, but I think John Surtees may have made a big mistake in fitting progressive springs to his racer, and it may have been a factor in his tank slapper and crash at Goodwood in 1998 (?).</p><p>I have always suspected but have been unable to prove that Girdraulics are very soft, perhaps dangerously soft, in the extended area of operation, but become too firm when compressed. So the last thing they need is progressive springs to increase this. Both John Surtees and Phil Irving commented that Girdraulic handling problems are most likely when the forks are extended. Conventional modern racers have in the main stopped using progressive springs in telescopic forks and now mostly use pull-down springs, which are degressive, the opposite of progressive. My standard geometry Girdraulics are certainly comfortable with soft degressive springs and I have had no handling problems.</p></blockquote><p></p>
[QUOTE="hadronuk, post: 75698, member: 1866"] I had to replace my spring cases as one could not be straightened sufficiently. On the test rig, the badly bent one was only producing an extra 4 - 6lbs of friction, but that was enough to give a very poor ride over smoother roads, as the forks remained stuck until a larger bump was encountered. The replacement cases from VOC Spares have a plastic lining in the larger diameter part of the outer case. These new cases in a test rig measured exactly the same as my less bent but very old and internally pitted case pair. Ride over smooth roads was much better, rough roads felt much the same. So I conclude that friction in the spring cases has a big impact on damping and comfort over smooth roads, but perhaps much less influence over rough roads. Secondly the plastic lining may be good for reducing wear, but not friction. So provided your old cases are straight, clean and well greased, there may be no functional benefit from replacing them. (Plus the dimensions of the new cases were wrong, resulting in too high a ride height. I did report this, it may be fixed now.) There is one other possible spring case problem. Some replacement springs were right on the top tolerance for diameter. This means that as they compress, expand and buckle they can jam in the cases. My suggestion that the original spring specification was wrong received a very frosty response from one very senior and knowledgable club member, but nervertheless, I believe a new batch of springs was made. It is probably extremely arrogant of me to say this, but I think John Surtees may have made a big mistake in fitting progressive springs to his racer, and it may have been a factor in his tank slapper and crash at Goodwood in 1998 (?). I have always suspected but have been unable to prove that Girdraulics are very soft, perhaps dangerously soft, in the extended area of operation, but become too firm when compressed. So the last thing they need is progressive springs to increase this. Both John Surtees and Phil Irving commented that Girdraulic handling problems are most likely when the forks are extended. Conventional modern racers have in the main stopped using progressive springs in telescopic forks and now mostly use pull-down springs, which are degressive, the opposite of progressive. My standard geometry Girdraulics are certainly comfortable with soft degressive springs and I have had no handling problems. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modified Steering Stem
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