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Thread: Fork air gap

  1. #1
    Senior Member
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    Fork air gap

    I have a new 2012 NCS that I picked up a week ago. I have been busy adjusting everything to suit me.

    The rear suspension sag seems spot on for me at 38mm or 32% of the 120mm travel. The front is a bit much at 45mm of 120, so I'm planning on adding a 7mm spacer under the fork cap and see where that puts me.

    My concern is that I'm only getting 100mm of travel on the front. This has been checked by using a "zap strap" around the fork tube and measuring where it ends up after an exuberant ride. Normally reduced travel is caused by too small an air gap, or too much fluid in the forks. I have not felt any harsh bottoming, so I believe that the forks are bottoming on the air cushion, as they should.

    Before I lower the level of fork oil, has anyone run into this problem, or should I be looking for another cause for the lack of travel?

  2. #2
    Senior Member Griff's Avatar
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    I will be interested to see the results of your testing etc. As these are budget forks it will always be difficult to improve on them. Rather than add spacers, a replacement progressive spring may be the way to go. However I do understand your thinking. My only adjustment so far has been to significantly increase the preload on the shock. After a ride out on rough roads yesterday, I now intend to increase the preload even more as there is too much sag.

  3. #3
    Senior Member treybrad's Avatar
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    I'll be interested to follow along and see what others have found. I think Honda quote 6" travel, but some reviews have listed 5.4". I've had a zip tie on my forks since installing the Ricor valves a couple months back, and don't think I've ever seen more than 5" of travel total when I took the time to measure.

    I measured more than that with the springs out of the tubes, sliding the fork bodies from full compression to extension (close to 6" I believe, but I'll have to find my notes to get that figure). That's the number I used to set my sag at 33%-ish, which means if I really only have 5" of travel, I'm closer to 40% sag. Never feel it bottoming harshly though.

    trey

  4. #4
    Junior Member jonnybegood's Avatar
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    I also have a zip tie on my fork tube to check travel. On my normal ride to work with out hard braking I only use 2 inches of travel even though I have a harsh ride over several cracks across the road. Under heavy braking I use 4.25 inches of travel. If Honda would have given us drain hole in the lower fork legs I think it would be easy to improve my ride with lighter oil and lower oil level.

  5. #5
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    So I added a 9mm spacer to the top of the factory spacer today. My sag with rider is now 36mm which is 30% of the total travel of 120. I'm happy with that as I measured it without my gear on. BTW the race sag, (bike only) is 21mm. There us a rule of thumb formula that compares race sag and rider sag and tells you if you need if you need stiffer or lighter springs. I don't know it off the top of my head, so I'll find it and post it.

    I reduced the fluid level by 10mm using my oil change sucker. Unfortunately I had no time for a test drive, so I'll keep you posted on the results.

  6. #6
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    This article explains a bit about spring rates and sag: Peter Verdone Designs - Motorcycle Springs

    In my case, I weigh 175 (w/o gear, as the measurements where taken) and the bike is 475. I'm guessing that the sprung weight of the bike to be 440 ish. So the total would be 615 and the bike is 71% of the load. Then bike sag (race sag or free sag) should be 71% of 36mm = 25.5mm. My readings for that number are 21mm, that would lead me believe that the spring rate is too soft for me. Since I'm after a smooth ride rather than ultimate track performance, I'm OK with that.

    Now for a test ride tomorrow.

  7. #7
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    After a quick test I still only have 100mm of travel.

    Next I'll have to pull the springs and see if they have enough travel, but I can't see Honda putting in springs that would bind before full travel is reached, and I would have felt a solid thunk like that. I'm not too keen on removing much more fluid.

    As to the above post, there is a flaw in my calculations as I am using total bike weight, not the front wheel weight. I have to sit and noodle a bit to come up with some better figures.

  8. #8
    Senior Member Fork air gap dduelin's Avatar
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    It's hard to tune a damping rid fork. The air gap doesn't come into play until the last 30% or so of travel.......Honda had to balance compression damping against spring rate and seemed to use too much compression damping with springs a little too soft. I weigh 155 in street clothes and +/- 180 geared up and my rider sag is 40% but the forks don't use anywhere near full travel under any condition encountered in 20,xxx miles. I might address this with spacers about 6 mm longer, a mix of Honda fork oil about 7 wt, and lowering the stock 103 mm oil level by 10 or 15 %.
    Dave

    GL1800
    NC700XD




  9. #9
    Senior Member Fork air gap maxwellian's Avatar
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    I'll chime in and say I'm very happy with my my Ricor cartridge emulators. Very easy install. I sucked the oil out, so no fork removal, no drilling. Just drop 'em in and change to 5W oil. Also adds the equivalent of I think ~10mm to the preload spacer.

  10. #10
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    I managed a pretty good 200+ mile ride this past weekend. The only time I get to 100mm of travel is under hard braking, rough roads only yield about 90mm of travel.

    I just happen to have most of a bottle of 7 wt fork oil, so I'll take Dave's advice next. I certainly find that washboard like surfaces really overwhelm the forks, certainly too much comp. dampening. The only real solution will be some sort of new valving cartridge so that high and low speed damping can be adjusted seperatly, but those will have to wait till the next fiscal period.

    In the mean time I will continue to experiment with little or no cost tweaks.

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