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<blockquote data-quote="timetraveller" data-source="post: 73689" data-attributes="member: 456"><p>The important thing at the front is to ensure that when the rider is on the bike the lower front link is just pointing upwards at the front. The Patrick Walker bike looks to be using an original Vincent damper with the short lower eyes. The Robert Lusk bike has Thorntons front and rear. Part of the days testing at Brand Hatch a week ago was testing the Thornton coil over damper at the rear. This has been modified so that a spacer can be inserted at the lower end between the piston rod and the lower mounting. Both riders were just touching the exhaust pipes and so a spacer with an extra 4 mm thickness was fitted to pack up the rear end. This gave 6 mm on the wheel spindle and solved the problem. However, this is all on top an already modified upper mounting which gives more than an inch of packing backwards so I cannot tell you the exact amount of additional spacing which has been used without measuring it. I can do that next week if wished. Regarding the total travel at the front. A cable tie was fastened around the inner spring box where it just touched the outer box. Then, after the race, we could see just how much it had been moved down. It was all the way to the bottom suggesting that either it was not tight enough and had slipped (it seemed tight) or that there was no more movement possible without shortening the outer spring box. Note that this is with 30 lbs/inch springs with 3" of pre-load. At the moment we think that that is too much pre-load but as that would mean even more movement at the front end and thus compound the problem with total travel. We already have 36 lbs/inch springs made which are what Chrislaun found to be suitable for him on his road bike. He also used 3" of pre-load so at the moment my guess is that what we are homing in on is a spring of about 36 lbs/inch with less pre-load for lighter bikes.</p><p>I did some experiments on my own bike about four months ago and wrote something up for MPH which Graham has accepted but not yet found space to include. In that, I show the path movement of the front wheel spindle, real not theoretical. Following that I removed the front damper and let the wheel fall as far as it can without the limit of the damper. I found that it can drop another inch but if this is done then the first half an inch of movement moves the wheel spindle forwards, which is what we are trying to avoid, but only be 0.1 of an inch. Provided that this first half an inch is used up when the rider sits on the bike that might be acceptable. We seem to be heading for a combination of damper length and lower eye height which will allow at least the extra half an inch of drop, and possibly the whole inch, combined with springs in the 30 to 36 lbs/inch range to provide the maximum possible movement and hopefully the most comfortable and safe ride possible.</p><p>I'm sorry that I did not take any photographs but perhaps Vibrac can do that tomorrow. It is not as easy as it sound though as in the pits the bikes are normally on their racing rear stands and thus the bikes are tilted. I can take picture of the Robert Lusk bike next week if you wish.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 73689, member: 456"] The important thing at the front is to ensure that when the rider is on the bike the lower front link is just pointing upwards at the front. The Patrick Walker bike looks to be using an original Vincent damper with the short lower eyes. The Robert Lusk bike has Thorntons front and rear. Part of the days testing at Brand Hatch a week ago was testing the Thornton coil over damper at the rear. This has been modified so that a spacer can be inserted at the lower end between the piston rod and the lower mounting. Both riders were just touching the exhaust pipes and so a spacer with an extra 4 mm thickness was fitted to pack up the rear end. This gave 6 mm on the wheel spindle and solved the problem. However, this is all on top an already modified upper mounting which gives more than an inch of packing backwards so I cannot tell you the exact amount of additional spacing which has been used without measuring it. I can do that next week if wished. Regarding the total travel at the front. A cable tie was fastened around the inner spring box where it just touched the outer box. Then, after the race, we could see just how much it had been moved down. It was all the way to the bottom suggesting that either it was not tight enough and had slipped (it seemed tight) or that there was no more movement possible without shortening the outer spring box. Note that this is with 30 lbs/inch springs with 3" of pre-load. At the moment we think that that is too much pre-load but as that would mean even more movement at the front end and thus compound the problem with total travel. We already have 36 lbs/inch springs made which are what Chrislaun found to be suitable for him on his road bike. He also used 3" of pre-load so at the moment my guess is that what we are homing in on is a spring of about 36 lbs/inch with less pre-load for lighter bikes. I did some experiments on my own bike about four months ago and wrote something up for MPH which Graham has accepted but not yet found space to include. In that, I show the path movement of the front wheel spindle, real not theoretical. Following that I removed the front damper and let the wheel fall as far as it can without the limit of the damper. I found that it can drop another inch but if this is done then the first half an inch of movement moves the wheel spindle forwards, which is what we are trying to avoid, but only be 0.1 of an inch. Provided that this first half an inch is used up when the rider sits on the bike that might be acceptable. We seem to be heading for a combination of damper length and lower eye height which will allow at least the extra half an inch of drop, and possibly the whole inch, combined with springs in the 30 to 36 lbs/inch range to provide the maximum possible movement and hopefully the most comfortable and safe ride possible. I'm sorry that I did not take any photographs but perhaps Vibrac can do that tomorrow. It is not as easy as it sound though as in the pits the bikes are normally on their racing rear stands and thus the bikes are tilted. I can take picture of the Robert Lusk bike next week if you wish. [/QUOTE]
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