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FJR Motorcycle Forums
Technical & Mechanical Problems
Setting sag and preload on new fork springs?
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<blockquote data-quote="MCRIDER007" data-source="post: 1325932" data-attributes="member: 329"><p>I spent about 40 minutes on the phone with Oso last night trying to figure out why he was having so many problems....which I originally thought were being caused by excessive preload due to a spacer that is still much too long. Excessive preload would result in a very low bike sag reading and would also make the fork cap very difficult to install.</p><p></p><p>However, he said the fork cap went on very easy. The bike sag was 20mm but additional sag when he sat on the back was only 2-3 mm....opposite of what I thought he had described in this thread. To further confuse the issue, adjusting the external preload didn't seem to change the sag numbers at all and his spacer reduction of 52-53mm seemed to be very close to what I had calculated based on the difference of spring length and rates.</p><p></p><p>At that point the only thing that I could thing of that would explain his sag numbers would be a hydraulic/air lock caused by excessive oil in the forks. He had used the OEM oil height of 92mm but the RT springs are much longer and he had also installed the RT spring guides...which together are probably displacing much more air than the OEM springs, making the "air spring" excessive. I think you mentioned that RT used to recommend a 130mm oil height which seems much more appropriate. We decided the best course of action would be change the oil height to 130mm, leave the current spacer length as is, reinstall and remeasure sag, and hope the external adjustments will give him the sag he wants.</p></blockquote><p></p>
[QUOTE="MCRIDER007, post: 1325932, member: 329"] I spent about 40 minutes on the phone with Oso last night trying to figure out why he was having so many problems....which I originally thought were being caused by excessive preload due to a spacer that is still much too long. Excessive preload would result in a very low bike sag reading and would also make the fork cap very difficult to install. However, he said the fork cap went on very easy. The bike sag was 20mm but additional sag when he sat on the back was only 2-3 mm....opposite of what I thought he had described in this thread. To further confuse the issue, adjusting the external preload didn't seem to change the sag numbers at all and his spacer reduction of 52-53mm seemed to be very close to what I had calculated based on the difference of spring length and rates. At that point the only thing that I could thing of that would explain his sag numbers would be a hydraulic/air lock caused by excessive oil in the forks. He had used the OEM oil height of 92mm but the RT springs are much longer and he had also installed the RT spring guides...which together are probably displacing much more air than the OEM springs, making the "air spring" excessive. I think you mentioned that RT used to recommend a 130mm oil height which seems much more appropriate. We decided the best course of action would be change the oil height to 130mm, leave the current spacer length as is, reinstall and remeasure sag, and hope the external adjustments will give him the sag he wants. [/QUOTE]
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FJR Motorcycle Forums
Technical & Mechanical Problems
Setting sag and preload on new fork springs?
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