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techtalk:evo:susp01b [2017/12/18 10:20]
ixl2relax [2014 XL1200T Front Fork Testing w/ Spring Rate Charts]
techtalk:evo:susp01b [2018/04/17 22:43] (current)
ixl2relax
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-| Front fork off the bike. I pulled the fork cap to let the \\ fork tube compress all the way. I added a zip tie \\ pushing it all the way down to the fork lower; then \\ added black electrical tape to mark the max working \\ range of the fork (3.63"​) ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|I drained all the oil because I do not want to have \\ any trapped air acting as another "​spring"​ during the \\ testing, then add the cap back on. I then took the \\ fork downstairs to place it in the gym equipment \\ testing rig and start loading up weight while \\ recording the compressed distance. The spring is \\ another weak one! 225 lbs, and the spring is more \\ than done... ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|Test results, a spring rate of 45.0 lbs/in!!! By knowing \\ the equation of the line (I use microsoft excel to do a \\ curve fit and tell me the equation of the line) and the \\ observed sag measurement of 1.31", I can figure out \\ the load running through the spring; 110 lbs. I can \\ also figure out the oem spacer length (1.13"​) ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) ✔|+| Front fork off the bike. I pulled the fork cap to let the \\ fork tube compress all the way. I added a zip tie \\ pushing it all the way down to the fork lower; then \\ added black electrical tape to mark the max working \\ range of the fork (3.63"​) ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|I drained all the oil because I do not want to have \\ any trapped air acting as another "​spring"​ during the \\ testing, then add the cap back on. I then took the \\ fork downstairs to place it in the gym equipment \\ testing rig and start loading up weight while \\ recording the compressed distance. The spring is \\ another weak one! 225 lbs, and the spring is more \\ than done... ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|Test results, a spring rate of 45.0 lbs/in!!! By knowing \\ the equation of the line (I use microsoft excel to do a \\ curve fit and tell me the equation of the line) and the \\ observed sag measurement of 1.31", I can figure out \\ the load running through the spring; 110 lbs. I can \\ also figure out the oem spacer length (1.13"​) ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) ✔|
  
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-|At 1.31", I am using up too much of the fork working \\ range of 3.63". At 0.25% of 3.63" = 0.91". I need to \\ cut a longer spacer of 1.52". to shift the dotted line \\ to the right. The OEM spacer is longer than 1.52". \\ That is because the spring does not come up close \\ to the cap so the OEM spacer has to close that gap \\ then add an additional ~1.13" to compress the \\ spring. My new spacer (PVC pipe cut to length) to \\ set a good front preload (at 25%) is going to be \\ 1.52" - 1.13" = 0.4" longer than the current OEM \\ spacer. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|+|At 1.31", I am using up too much of the fork working \\ range of 3.63". At 0.25% of 3.63" = 0.91". I need to \\ cut a longer spacer of 1.52". to shift the dotted line \\ to the right. The OEM spacer is longer than 1.52". \\ That is because the spring does not come up close \\ to the cap so the OEM spacer has to close that gap \\ then add an additional ~1.13" to compress the \\ spring. My new spacer (PVC pipe cut to length) to \\ set a good front preload (at 25%) is going to be \\ 1.52" - 1.13" = 0.4" longer than the current OEM \\ spacer. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|
  
   * I'm will experiment a little on the front fork with some water to account for the "air spring"​. This will help me when riding to not bottom out and figure out what what rate spring to get.   * I'm will experiment a little on the front fork with some water to account for the "air spring"​. This will help me when riding to not bottom out and figure out what what rate spring to get.
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-|This shows the affect of "​compressing the air \\ chamber"​. If I had a 3" air column (at atmospheric \\ pressure of 14.7 psi) and compressed it in half, \\ the pressure would double to 29.4 psi. If I kept \\ cutting the distance in half (next would be to 0.75"​),​ \\ the pressure keeps doubling. You can see what \\ happens to the pressure. If you add a Schrader \\ valve and add 5 more psi, you get the red line on \\ the graph. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|A fork example: On the left you see the fork with oil \\  and air chamber. Next pic over is that fork \\ compressed. The air chamber is now 1/2 the volume \\ it was. Third pic is the same fork with some extra oil \\ in it. 4th figure is the compressed fork with the extra \\ oil in it. You can see the air chamber is now only \\ 1/5th the air volume. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|The affect of the changing air chamber can be seen \\ in this graph. I am in effect moving up further on the \\ psi curve. The additional air pressure acts as a \\ spring, hence, why I call it the air spring. This air \\ spring affect is additive to the steel OEM spring to \\ help me keep from bottoming out. Its the cheap way \\ of finding the spring rate I need for the bike.  ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|+|This shows the affect of "​compressing the air \\ chamber"​. If I had a 3" air column (at atmospheric \\ pressure of 14.7 psi) and compressed it in half, \\ the pressure would double to 29.4 psi. If I kept \\ cutting the distance in half (next would be to 0.75"​),​ \\ the pressure keeps doubling. You can see what \\ happens to the pressure. If you add a Schrader \\ valve and add 5 more psi, you get the red line on \\ the graph. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|A fork example: On the left you see the fork with oil \\  and air chamber. Next pic over is that fork \\ compressed. The air chamber is now 1/2 the volume \\ it was. Third pic is the same fork with some extra oil \\ in it. 4th figure is the compressed fork with the extra \\ oil in it. You can see the air chamber is now only \\ 1/5th the air volume. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|The affect of the changing air chamber can be seen \\ in this graph. I am in effect moving up further on the \\ psi curve. The additional air pressure acts as a \\ spring, hence, why I call it the air spring. This air \\ spring affect is additive to the steel OEM spring to \\ help me keep from bottoming out. Its the cheap way \\ of finding the spring rate I need for the bike.  ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|
  
   * As far as the psi scale up to 2,000 psi, what I posted was math extrapolations. I did not set up something, then measured it. I suspect the fork seals would not hold anything close to that pressure. Perhaps a few hundred psi max? If you had too much oil in, I suspect you would see weeping of oil on the fork tubes as well as experiencing the "hydro locking"​ condition. BTW, you are not adding 2,000 psi but just starting at atmospheric pressure and squeezing the air volume from 3" tall to 0.03" tall which makes the pressure go to ~2,000 psi...   * As far as the psi scale up to 2,000 psi, what I posted was math extrapolations. I did not set up something, then measured it. I suspect the fork seals would not hold anything close to that pressure. Perhaps a few hundred psi max? If you had too much oil in, I suspect you would see weeping of oil on the fork tubes as well as experiencing the "hydro locking"​ condition. BTW, you are not adding 2,000 psi but just starting at atmospheric pressure and squeezing the air volume from 3" tall to 0.03" tall which makes the pressure go to ~2,000 psi...
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-|By having the volume of water for each point, I can \\ see the curve of options vs max fill ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|The true test of what the oil does comes from the weight testing. Here you can see what the spring alone does. As the weights are piled in increasing amounts, you can see the fork can hold up more weight for a given load - that is because of the help from the "air spring"​. At a 70% oil fill, the fork can hold up an extra 61 lbs (214 to 275) before bottoming out. I next tested the "add an extra ounce" option taking the fork to a 76 % fill. You can see from the red line, the fork doesn'​t bottom out even with 385 lbs on it. I test one more point, a 73.5 % fill, and it looks to be the one to go riding with. It looks like it would come very close to bottoming out but only after it adds another ~ 100 lbs (~320 vs 214) of capacity. Hopefully this will be enough to keep me from bottoming out tomorrow. But, for short forks, maybe only add a half ounce. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|+|By having the volume of water for each point, I can \\ see the curve of options vs max fill ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|The true test of what the oil does comes from the weight testing. Here you can see what the spring alone does. As the weights are piled in increasing amounts, you can see the fork can hold up more weight for a given load - that is because of the help from the "air spring"​. At a 70% oil fill, the fork can hold up an extra 61 lbs (214 to 275) before bottoming out. I next tested the "add an extra ounce" option taking the fork to a 76 % fill. You can see from the red line, the fork doesn'​t bottom out even with 385 lbs on it. I test one more point, a 73.5 % fill, and it looks to be the one to go riding with. It looks like it would come very close to bottoming out but only after it adds another ~ 100 lbs (~320 vs 214) of capacity. Hopefully this will be enough to keep me from bottoming out tomorrow. But, for short forks, maybe only add a half ounce. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|
  
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-|76% fill is too much; it can hold up a lot, but it not a \\ useful suspension range as its all in the last fraction \\ of an inch. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|Fork is cleaned up and air dried overnight. This pic \\ shows the critical dimensions. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=8)) →|+|76% fill is too much; it can hold up a lot, but it not a \\ useful suspension range as its all in the last fraction \\ of an inch. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|Fork is cleaned up and air dried overnight. This pic \\ shows the critical dimensions. ((Pic by spacetiger of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=8)) →|
  
  
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-|This shows the max range from the front suspension; \\ it varied between 233 and 290. Based on the sag \\ numbers, I can determine the riding envelope and \\ can pick a suitable spring and longer damper rod \\ to extend the length of the fork ((Pic by spacetiger http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=11)) →|This shows the max range of the rear suspension; it \\ varied between 657 and 690. Again, based on the \\ sag numbers, I can determine the riding envelope \\ and can project how the Frankenshocks will \\ perform. ​ ((Pic by spacetiger http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=11)) →|For the front suspension, I have ordered the front \\ race tech springs. They are linear rate springs. I went \\ with linear rate springs because the addition of oil will \\ make the upper range progressive,​ so there was no \\ need to get a progressive rate spring. ((Pic by spacetiger http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=11)) →|+|This shows the max range from the front suspension; \\ it varied between 233 and 290. Based on the sag \\ numbers, I can determine the riding envelope and \\ can pick a suitable spring and longer damper rod \\ to extend the length of the fork ((Pic by spacetiger http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=11)) →|This shows the max range of the rear suspension; it \\ varied between 657 and 690. Again, based on the \\ sag numbers, I can determine the riding envelope \\ and can project how the Frankenshocks will \\ perform. ​ ((Pic by spacetiger http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=11)) →|For the front suspension, I have ordered the front \\ race tech springs. They are linear rate springs. I went \\ with linear rate springs because the addition of oil will \\ make the upper range progressive,​ so there was no \\ need to get a progressive rate spring. ((Pic by spacetiger http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=11)) →|
  
   * I also ordered the longer damper rods:   * I also ordered the longer damper rods:
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-|The rear shocks are ready to go on. This will let me \\ see how to finish packaging the front suspension \\ based on the taller rear to get the rake and trail \\ numbers I was hoping for. I also need to see how \\ the 1200S shocks work with the bags… or not. ((Pic by spacetiger http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=11)) →|The new spring rates are very similar to what came \\ OEM. Perhaps the rear are about 6% softer. I’ll play \\ with the geometry during the week just to take a \\ closer look at the rates. But so far no show stoppers, \\ I just have a bit more work to go. Perhaps a couple \\ more weekends and the suspension work should be \\ done.  ((Pic by spacetiger http://​xlforum.net/vbportal/​forums/​showthread.php?​t=1863121&​page=11)) →|+|The rear shocks are ready to go on. This will let me \\ see how to finish packaging the front suspension \\ based on the taller rear to get the rake and trail \\ numbers I was hoping for. I also need to see how \\ the 1200S shocks work with the bags… or not. ((Pic by spacetiger http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=11)) →|The new spring rates are very similar to what came \\ OEM. Perhaps the rear are about 6% softer. I’ll play \\ with the geometry during the week just to take a \\ closer look at the rates. But so far no show stoppers, \\ I just have a bit more work to go. Perhaps a couple \\ more weekends and the suspension work should be \\ done.  ((Pic by spacetiger http://​xlforum.net/​forums/​showthread.php?​t=1863121&​page=11)) →|