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Thread: Front Fork Sag, help the new guy understand

  1. #1
    Bike: 72 Shovelhead and a 2012 NC700X DCT
    Join Date
    Apr 2018

    Question Front Fork Sag, help the new guy understand

    First of all let's make sure I have my terms right:

    Free sag = the difference between fully extended and the bike upright with no rider
    Mine is 3/8" or 9.5mm

    Static or "Race" Sag
    = the difference between fully extended and the bike upright with rider in riding position
    Mine is 2 3/16" or 55.56 mm (41% if true total front travel is 5.4" 137.16mm)

    So, as I understand from other threads most people have more free sag than I do (30mm to 45mm) And about the same static sag at 52mm to 63mm.

    So, help me understand why my free sag is so small? Too much pre-load? I pulled the cap off and the spacer appeared to be stock and there was very little resistance to get the threads started again.

    I think I also read that very little free sag and lots of static say says the springs are too soft.

    Part of me wants to add 11/16" to the spacer length to get the Static Sag back to about 30% of total and to get some travel back. Is that a bad idea? If not, is PVC pipe okay to use for the spacer like the dirt bike guys do?

    I weigh about 190 without gear but I did have the top box and panniers on the bike, about half a tank of fuel. The previous owner was 300+ I don't think that should have done any permanent damage to the springs but what do I know.

    Anything you can share will certainly make me smarter which is a good goal in and of itself, but I am really trying to figure out what to do to tame the washboards some. I figured to start with pre-load before I buy emulators and a rear shock and start messing with spring rates.

  2. #2
    Senior Member Front Fork Sag, help the new guy understand
    Front Fork Sag, help the new guy understand
    DirtFlier's Avatar
    Bike: 2013 NC700x/w DCT
    Join Date
    Dec 2014
    Troy, Ohio
    It's normally called "unladen sag," and not free sag.

    Settling only 10 mm seems like a small number to me. My guess is that adding spacer length to reduce the 10 mm number will result in feeling every tiny crack or bump on the roads. With too much preload, the front tire can't drop into a depression because it's already fully extended so hits the other side with a harsh bang. You want the tires to roll into the depression so suspension damping can take up the impact of hitting the other side.

    On both of my Honda bikes, the other one is an NT700V, fork compliance was improved by reducing preload and making the fork oil height closer to the top. The increased oil height slows fork compression as it nears full travel but otherwise can't be felt.

  3. #3
    Senior Member
    Bike: Nc700x
    Join Date
    May 2016
    So adding fluid to the fork will do what?; soften or make more harsh the feel of the forks upon a bump in the road.
    I find my forks on the 700x to be damn abrupt and harsh......a jolting affect. Not pleasant.

  4. #4
    Member Front Fork Sag, help the new guy understand
    Bike: 12 NC700x
    Join Date
    Oct 2013
    Horicon, WI
    By all the formulas, the front fork springs are to soft. Most of the spring calculators are going to put you in the .9 kg/mm range. Stock on this bike is around .63 although it is not a linear rate spring so the actual rate depends on where in the travel you are. I think it would be worth while to upgrade the spring. I did some experimenting on a DL650 which had similar travel and weight and started with a .95 rate which I found too stiff. Dropped to a .90 and it was better for me. I think the sweet spot would be around .80 to .85. It all depends on your personal preferences.

    Better performance on washboard roads is going to take more than the right spring though. The compression damping hole on the fork is very small which limits the ability of the fork to respond to sharp high speed impacts. You are probably going to need something like a gold valve emulator which specifies drilling out the compression damping hole to a larger size.

    I agree with DirtFlier. adding preload is not really going to help your situation.
    Last edited by Lee Dodge; 2nd October 2018 at 20:32.

  5. #5
    Junior Member
    Bike: 2012 NC700X and 2018 Goldwing
    Join Date
    Dec 2018
    Dubuque Iowa
    If the previous owner was 300 pounds maybe he installed stiffer fork springs.

  6. #6
    Senior Member Front Fork Sag, help the new guy understand
    Front Fork Sag, help the new guy understand
    DirtFlier's Avatar
    Bike: 2013 NC700x/w DCT
    Join Date
    Dec 2014
    Troy, Ohio
    [...So adding fluid to the fork will do what?..]

    Speaking in general terms, adding more fluid to the fork will make it stiffer in the last part of its travel. Think of the column of oil inside a fork as a piston that moves up and down. Adding oil to it is similar to fitting a higher compression piston - it'll be more difficult to compress at the top of the stroke.

    Fork oil is usually measured in "inches (or MM) from the top" with the spring removed and fork completely collapsed. This is the most accurate way of measuring fork oil and not by counting ounces that you've added/subtracted. Without this measurement, you're just guessing at what you're doing.

  7. #7
    Senior Member Front Fork Sag, help the new guy understand
    Bike: BMW, KTM, Aprilia
    Join Date
    Jun 2013
    California, USA
    If you set your "race sag" to the amount you are looking for, and you find that you have very little or no "unladed" or "free" sag, that means that the springs are too soft for your weight.

    Essentially what is happening is you are having to add so much preload to the spring (stiffness) to prevent it from sagging to much under your weight, that when you take your weight off, the spring is "too stiff" for the bike.

    So, if you want to get your free sag and race sag within the numbers you mentioned, it would appear that you would need stiffer front springs.

    As to oil, more oil in a fork means a STIFFER fork when moving. It won't affect your race sag or free sag.

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