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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Prototype of new AVO coilover for Series ‘D’ Vincents
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<blockquote data-quote="hadronuk" data-source="post: 97992" data-attributes="member: 1866"><p>By lower, I take it you mean lower spring rate? In short –yes. You are right that the original B/C springs together were about 390 lbs/inch and I gather the D usually used a 380 lbs/inch spring. However, the B/C setup was extraordinary because the shortness of the springs gave a substantial negative preload, so that very little of the available damper travel was used.</p><p></p><p>So within limits, more preload and better quality damping, both adjustable, undoubtedly allows softer springing, giving better comfort and grip.</p><p></p><p>The question of course is exactly how much softer?</p><p></p><p>It is a difficult decision, because it is an engineering and individual compromise between so many different factors. The weight of the rider, acceptable seat height, local roads, how fast you ride, how much bottoming out is acceptable, etc.</p><p></p><p>My decision to make 275lb/inch the default was perhaps a bit bold. The safe choice would have been, say 350 lbs/inch. But I felt that 275 would work for the majority of riders, who if saddled with a default 350 spring would be losing out somewhat on ride quality. Big Ed frequently uses his Rapide two up with the 275 spring and finds it is still acceptable.</p><p></p><p>Regarding your particular situation, the first thing I would say is that in my view if suspension never bottoms out it is too stiff. My local roads have some appalling bumps and pot holes to the extent it is just not possible to steer round all of them. A spring stiff enough to never bottom out would be far too stiff the rest of the time. I’ve tried it!</p><p></p><p>Checking my notes, it is not advisable to set the 275 spring preload to shorten the spring more than 6.625 inches unloaded. If you do, it is possible the spring may become coil bound before the bump stop fully does its job. If you find that is still insufficient, have you tried a modest increase in damping stiffness? If you want to try a stiffer spring they are available in increments of 25 lbs/inch. But step changes in wire size etc. means some have better closed lengths than others. Although 300 and 325 springs are available in this range, the next “sweet spot” is 350 lbs/inch.</p><p></p><p>Incidentally, I have found a cheap spring compressor on Ebay that makes changing springs an easy job. I will find a link if anyone is interested.</p><p></p><p>With regard to the D, the original setup is much better than the original B/C, as it has some spring preload and better quality damping. But when dyno tested it still seemed rather underdamped, so given the substantial damper travel and now adjustable damping and preload, I feel 300 lbs/inch should be fine, quite a safe choice in fact. We will see!</p><p></p><p>TT -Thanks for your useful and timely comments.</p></blockquote><p></p>
[QUOTE="hadronuk, post: 97992, member: 1866"] By lower, I take it you mean lower spring rate? In short –yes. You are right that the original B/C springs together were about 390 lbs/inch and I gather the D usually used a 380 lbs/inch spring. However, the B/C setup was extraordinary because the shortness of the springs gave a substantial negative preload, so that very little of the available damper travel was used. So within limits, more preload and better quality damping, both adjustable, undoubtedly allows softer springing, giving better comfort and grip. The question of course is exactly how much softer? It is a difficult decision, because it is an engineering and individual compromise between so many different factors. The weight of the rider, acceptable seat height, local roads, how fast you ride, how much bottoming out is acceptable, etc. My decision to make 275lb/inch the default was perhaps a bit bold. The safe choice would have been, say 350 lbs/inch. But I felt that 275 would work for the majority of riders, who if saddled with a default 350 spring would be losing out somewhat on ride quality. Big Ed frequently uses his Rapide two up with the 275 spring and finds it is still acceptable. Regarding your particular situation, the first thing I would say is that in my view if suspension never bottoms out it is too stiff. My local roads have some appalling bumps and pot holes to the extent it is just not possible to steer round all of them. A spring stiff enough to never bottom out would be far too stiff the rest of the time. I’ve tried it! Checking my notes, it is not advisable to set the 275 spring preload to shorten the spring more than 6.625 inches unloaded. If you do, it is possible the spring may become coil bound before the bump stop fully does its job. If you find that is still insufficient, have you tried a modest increase in damping stiffness? If you want to try a stiffer spring they are available in increments of 25 lbs/inch. But step changes in wire size etc. means some have better closed lengths than others. Although 300 and 325 springs are available in this range, the next “sweet spot” is 350 lbs/inch. Incidentally, I have found a cheap spring compressor on Ebay that makes changing springs an easy job. I will find a link if anyone is interested. With regard to the D, the original setup is much better than the original B/C, as it has some spring preload and better quality damping. But when dyno tested it still seemed rather underdamped, so given the substantial damper travel and now adjustable damping and preload, I feel 300 lbs/inch should be fine, quite a safe choice in fact. We will see! TT -Thanks for your useful and timely comments. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Prototype of new AVO coilover for Series ‘D’ Vincents
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