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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
New Coilover for Girdraulics
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<blockquote data-quote="timetraveller" data-source="post: 101716" data-attributes="member: 456"><p>Here are some thought on the subject. For the JE modification I did lots of tests before coming up with the final specification for springs etc. The test riding of Chris Launders was a great help with this. At one stage I had a distance scale on an empty AVO damper and another on one of the spring boxes to determine whether there was a ratio in their movements. If there is one then it was too small for me to determine and my opinion is that the there is a one to one ratio between spring box compression and the damper compression.</p><p>Chris weighs 20 stone, 280 lbs, 127 kgs and with 45 lbs/inch springs with 2" of preload required about half an inch of extra packing on the springs. I think that give 225 lbs of preload for that rider. We also had to go for stiffer dampers than the standard dampers as soon as we replaced the Oilite bushes with bearings (needle rollers in Chris' case). I have been supplying the 45 lbs/inch springs to all twin riders and it has become clear that for lighter riders they are too strong and it is slowly becoming clear that for normal use on European roads, even two up with luggage, a twin is better off with the 36 lbs/inch springs with 3" of preload and a standard AVO damper. I make that 216 lbs of pre-load but with an easier movement for tackling bumps. Note that Greg in Australia is finding that they like 45 lbs/inch springs even on Comets and I have no explanation as to why this is. Riders over here certainly find that too stiff. For Comets I supply 33 lbs/inch springs with 3" of pre-load (198 lbs pre-load) but some people are also wanting to try 30 lbs/inch springs on Comets, 180 lbs of pre-load. Note that there are two things here, One is the pre-load to try and get the starting angle of the lower link correct and then the ease at which the front end can compress to handle bumps. </p><p>I did design a method for building pre-load adjustment into the front spring boxes. A drawing for that is included with every set of fitting instructions for the JE mod. So far no one has chosen to try that option.</p><p>I do not pretend to be an expert on suspension but from what I understand from the above the damper has to work harder when there is less friction and more spring force. It seems not to be just a matter of altering the pre-load but also the spring rate and in conjunction with that the damping rate. So for the proposed front coil overs the adjustable damper and pre-load adjustment is going to be vital but the spring rate will not be variable and, extrapolating from experience with the JE modification, it is going to require a choice of spring rates to suit different weights of bike and rider. What seems not to affect any of this is the weight of any pillion passenger and/or luggage. My guess is that they are so far back that their weight is taken by the rear suspension.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 101716, member: 456"] Here are some thought on the subject. For the JE modification I did lots of tests before coming up with the final specification for springs etc. The test riding of Chris Launders was a great help with this. At one stage I had a distance scale on an empty AVO damper and another on one of the spring boxes to determine whether there was a ratio in their movements. If there is one then it was too small for me to determine and my opinion is that the there is a one to one ratio between spring box compression and the damper compression. Chris weighs 20 stone, 280 lbs, 127 kgs and with 45 lbs/inch springs with 2" of preload required about half an inch of extra packing on the springs. I think that give 225 lbs of preload for that rider. We also had to go for stiffer dampers than the standard dampers as soon as we replaced the Oilite bushes with bearings (needle rollers in Chris' case). I have been supplying the 45 lbs/inch springs to all twin riders and it has become clear that for lighter riders they are too strong and it is slowly becoming clear that for normal use on European roads, even two up with luggage, a twin is better off with the 36 lbs/inch springs with 3" of preload and a standard AVO damper. I make that 216 lbs of pre-load but with an easier movement for tackling bumps. Note that Greg in Australia is finding that they like 45 lbs/inch springs even on Comets and I have no explanation as to why this is. Riders over here certainly find that too stiff. For Comets I supply 33 lbs/inch springs with 3" of pre-load (198 lbs pre-load) but some people are also wanting to try 30 lbs/inch springs on Comets, 180 lbs of pre-load. Note that there are two things here, One is the pre-load to try and get the starting angle of the lower link correct and then the ease at which the front end can compress to handle bumps. I did design a method for building pre-load adjustment into the front spring boxes. A drawing for that is included with every set of fitting instructions for the JE mod. So far no one has chosen to try that option. I do not pretend to be an expert on suspension but from what I understand from the above the damper has to work harder when there is less friction and more spring force. It seems not to be just a matter of altering the pre-load but also the spring rate and in conjunction with that the damping rate. So for the proposed front coil overs the adjustable damper and pre-load adjustment is going to be vital but the spring rate will not be variable and, extrapolating from experience with the JE modification, it is going to require a choice of spring rates to suit different weights of bike and rider. What seems not to affect any of this is the weight of any pillion passenger and/or luggage. My guess is that they are so far back that their weight is taken by the rear suspension. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
New Coilover for Girdraulics
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