• JINKSTER ATTACKS "SUSPENSION"

    This long post is for those of you who may be like me and use/ride your Hayabusa as "The Ultimate Hyper Sport Tourer".

    While the Busa is blessed with one he11 for power engine it's stock suspension leaves much to be desired by the curve slicing road warriors amoungst us. To wit?..it's front forks simply lack the same amount of travel normally found in full blown RR type sportbikes which to me means that it is that much more important that we make the most of what little suspension travel we do have. Also?...while attending this last Busa Bash at Deals Gap I promised a bunch of members here that when I did get the chance to properly address my new-to-me Busa's suspension that I would share that information here with the members of hayabusa.org...this is me fulfilling that promise.

    "MOTORCYCLE SUSPENSION" is a deep subject...a physics ruled applied science with so much to know that I will only touch on the necessary parts of it here and be as concise as possible which will hopefully include enough information that you can make the most out of...

    "ADJUSTING YOUR BUSA'S STOCK SUSPENSION FOR HIGH PERFORMANCE RIDING."

    RULE #1: Forget everything the Service Manual or Owners Manual recomends as those settings and adjustments are extremely generic in nature and only meant as a starting point recomendation for riders of grossly varying and unknown weights...as in...ya might as well consult "The Guesser" at the county fair and in a word?..hooey...now here's how to do it the right way.

    "Measuring Static/Sag": is really a misnomer as what you'll be measuring are these three suspension measurements (both front & rear)...

    1. "Full Extension" (just what it implies..your forks and/or shock fully extended and this measurement is taken only for purposes of baseline reference)

    2. "Static Sag"(or free sag...which is the amount of compressed travel under JUST the weight of the bike alone) and finally...

    3. "Laden Sag" (the total amount of compressed travel with both the weight of the bike itself AND the rider aboard)

    Note: "FULL EXTENTION" measurements are not 5to be confused with "Actual Suspension Travel" and are only for use as reference dimensions from which to base your sag settings from as already know that "The Actual Suspension Travel Specs" for the Hayabusa are...

    FRONT: 4.7" (120mm)

    REAR: 5.5" (140mm)

    So do not confuse "Full Extension" with or assume that it is "Actual Suspension Travel".

    The mission here is to attempt to compress approx. 33% (1/3rd) of the suspensions actual travel as "Laden Sag Compression" both front and rear. Lighter or Heavier riders may have to re-spring. I weigh 240 and will have to re-spring my front as it is way too soft but I was just barely able to attain *NEAR good performance settings by socking down the spring preload adjusters and stiffening up the compression rebound settings.

    "THE FRONT FORKS"

    With the 1 1/4" Genmar Riser I already had an added level of difficulty but it worked out to my advantage as instead of eye-balling the 8 engraved lines on the spring pre-load adjusters?...I counted revs by marking my 17mm socket and spinning them all the way out from flush for a total of 12 counted revolutions like so...



    I had already measured the FULL EXTENDED distance of my front forks previousely (while the lower fairing was off and I had the front wheel freely suspended off the ground with the forks at full unladened extention) and that distance measured right at 5 inches from the bottom side of the dust cover to the top side of the cast fork end.

    With the adjusters socked down too flush with the fork cap (max spring preload) my static sag dimension was 3.950"

    With the adjusters spun out too 12 revs out (minimum spring preload) my static sag dimension measured 3.450...



    which represented a full 1/2" of adjustability by tuning/setting the spring end play by using the spring preload adjusters. I settled on taking the preload adjusters a full 10 revs in (from 12 revs locked all the way out) to achieve a static sag dimension of 3.850"....or 1.150 static sag compression..which basically sux as just the static weight of the Busa itself has ate up 28mm of compression on me and I haven't even gotten around to plopping my lard@$$ on it yet...and now for the important part...

    33% of 4.7" (actual travel) ='s 1.551 (as "Laden Sag" Compression)...

    5" (FULL EXTENTION) - 1.551 = 3.449"

    That's "The Magic Number" folks...PROPER LADEN SAG SHOULD BE 3.449 That's the measurement you want between the top of the cast fork end the the bottom of the fork seal dust cover..and measured as follows...with the bike resting static on a rear stand place a zip tie here like so...



    Then gently mount the bike (while it's on it's rear stand) slowly lifting your feet to the pegs and assuming your riding position...then gently dismount the bike and then measure like so and HERE is where your looking to hit that magical 3.449 "Laden Sag" dimension...



    As you can see it's apparent that I missed my magic number by about .300 and had about 7mm to much laden compression which indicates to me that the springs are too weak..as I suspected they would be due to the fact that the static weight of the bike itself had already gobbled up the lions share of compression before my @$$ ever hit the seat (and that's the impotance of taking "Static Sag" measurements)...and IMHO the Busa flat out needs stiffer springs up front...and that goes for anybody...sans any sub 150lb flyweights who might get away with using the stock oem fork springs..but I wouldn't recomend it..the Busa has proven to me it needs stiffer fork springs....and now the good news...

    "ADDRESSING THE REAR SHOCK"

    All the same factors previously discussed apply here as well and I had far better luck here...

    The rear (like the front) seemed gushy and wallowy to me..especially when up at the Busa Bash...and here we go...

    The first measurement needed is "Full Extension"...for this I had to devise a way to suspend the rear wheel in the air with the swingarm/shock unladened of any sprung weight...which I did like so...using a rear stand, a pair of jack stands and a length of 5/8ths steel rod...like so...





    once the rear wheel/swingarm is freely suspended put a piece of electrical tape on the outboard most area of your ductail to use as a measuring reference point and measure from the top of the swingarm end flat like so...



    And that's your "Fully Extended" measurment...now...before you lower the bike back down?..(and trust me here)...Page 36 of your owners manual will tell you that you need a special tool to adjust the shocks spring preload...they lied...just take a drift and a hammer and go in there and spin that top jam collar off the adjustment collar in a counter clockwise direction and put a dab of paint for a ref. starting point like so...



    and then using your drift and hammer drift/spin the adjusting collar two full revs/threads downward (clockwise)...this will put an approx. additional 4 mm of preload on your shocks spring like so...



    then lock that jam collar back down snugly and set your compression damping (top screw) at 7 clicks out and your rebound damping (bottom screw) at 10 clicks out...you'll love the results...or just do the math and tune to your own taste and body weight.

    I know this...my Busa's suspension was way too soft and very vague feeling to me...I exploited the fork damping a bit to kinda cheat a tad and make up for the weak/soft fork springs by setting compression damping up front too just 4 clicks out and rebound damping to just 3 clicks out and even though I know my busa needs heavier front fork springs?...these adjustments and settings made a world of difference in how she handles now...no more squating in the rear under acceleration and she dosen't dive in the front (during hard braking) anywhere's near as badly as she used to..heck...just the massive torque and engine braking used to be able to have her rocking back and forth like riding a freaking hobby horse...but not anymore as just addressing sag dimensions and settings has proven to yeild a vast improvement...and now I just need to order slightly heavier fork springs.

    Hope that helps and "Promise Fulfilled"...L8R, Bill.



    <!--EDIT|JINKSTER
    Reason for Edit: "if it helps my busa bretheren it belongs here"|1144273012 -->
    This article was originally published in forum thread: JINKSTER ATTACKS "SUSPENSION" started by JINKSTER View original post