JINKSTER ATTACKS "SUSPENSION"





JINKSTER

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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...

HFS4.jpg


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...

HFS1.jpg


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...

HFS2.jpg


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...

HFS3.jpg


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...

HRS1.jpg


HRS2.jpg


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...

HRS3.jpg


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...

HRS4.jpg


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...

HRS5.jpg


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.
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JINKSTER

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You are all very welcome and for as much knowledge as I extract from this board for my own personal use I'm more than happy to be able to share some information myself. Furthermore...after my findings of just how softly sprung the Busa's stock/oem front forks are?... (28mm Static Compression is just waaay too soft)..I see this as a rather important issue...one that needs addressing because no matter how skilled of a rider anyone here may be?....if you run out of fork travel on a 500lb bike you are in deep pooh...no matter who you are.

I'll be calling around for heavier springs soon...possibly even today...if you guys do decide to make this a sticky I will maintain this thread by adding a small tutorial "How To" as I swap out to heavier springs.

Thanks again and L8R, Bill.
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JINKSTER

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BTW...this may explain why silly $hit happens like "Dragging The Fairing" as i'd almost bet that happens as a result of the front end being too softly sprung as it comes from the factory.

L8R, Bill.
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vman1300

Never Forgotten
BTW...this may explain why silly $hit happens like "Dragging The Fairing" as i'd almost bet that happens as a result of the front end being too softly sprung as it comes from the factory.

L8R, Bill.
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Thaks for the great write up Bill. I know I have been pushing the limits on the stock suspension for sometime. In the not too far future, I will have to address that issue. I want to make a few track days to improve my twisties skills and I know a properly set up suspension will only help.
 

ksheldon

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Jinkster,

Check with Lindeman Engineering in San Jose, CA - www.le-suspension.com.

They set up alot of AMA and AFM bikes and are a great source for springs and shocks.

I am planning on taking my bike to them and having them re-spring and re-valve the front forks.

Jim is a great source of information as well.

Kent
 

JINKSTER

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Update: I just got off the phone with some friends in the business whom I've had the rare privilage of briefly working alongside of and learning from...who also happen to be the same guys who set-up the suspension on Lee Shierts record holding Busa and Lee's latest 200+ '05 GSXR1000 project bike...to wit...Max MCcallister and Lee and Martin of "TRAXXION DYNAMICS" and when I ran my front fork sag dimensions by Lee just moments ago he was like.."My god...that's like cruiser suspension sag numbers!!! LOL!!!"...and I agree..and did what I already knew I should do and went ahead and ordered up a set of stiffer front fork springs to facilitate proper front end suspension of my Busa per my 240lb rider weight by selecting Lee and Martins recommendation of 1.1 rate Traxxion OMNI Springs which incorporate a nylon buffer/spacer system much like what is used in top level dirt bike suspension except..made and calibrated for the Busa whereby the nylon buffer slides over the internal cartridge rod and into the ID of the spring itself which entraps the fork spring central to the internal cartridge rod (so it dosen't mislocate center and wind up sqeaking against the fork tube ID) annnnd....prevents the spring from "Bowing In The Middle" when uder great load.

The 1.1 Straight Rate Omni Springs ran me $109...the buffer/spacer kit was $14.95 and the fork spring compressor tool was $29.95...all together about $160 including shipping...but money well spent considering the possible alternative as...when your screaming like a woman cause you came into the curve of a decreasing radius a little to hot is no time to decide to upgrade your Busa's suspenders!!! I'll just tell the wife it's "Cheap Insurance". LOL!!!

But seriousely folks...the good news is that the stock oem rear has plenty of support and travel for spirited riding (provided it's properly adjusted) but...the front suspension on the Busa sux...as not only is the overall usable fork travel shorter than what's on RR type sprtbikes?..but according to the static sag numbers it's also sprung far to soft...for anyone..and imho?...(and Lee's)..together that's a recipe for disaster.

Vman: I had to do something to safely keep up with your huge ultra fast @$$!!! LOL!!! BTW...In speaking with Lee at traxxion he asked if we had any heavy duty riders as Traxxion is trying to come up with proper spring weight dynamics on the busa's rear shock to adequately and proper advise/accomodate the heavier riders amoungst us...I mentioned that your one he11uva rider and looking to do future track days with your busa...and they need to get some baseline numbers by putting a stock oem rear shock spring on their "Spring Dyno"...call Lee at traxxion...tell'em Bill Jinks sent ya..I'm certain they'll be happy to have ya ship'em your rear shock and maybe cut ya a brake...if not at least give ya some great suspenders to match rider weight for you...I've been in the hot pits with Max and his crew at Daytonas CCS championships...they know their pooh.

L8R, Bill.
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cutter

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Nice write up Bill. Thanks for the tips.

I finally got around to tuning the suspension in my 2mo old Busa last rainy weekend. Same deal- factory settings appropriate for your average 140lb Japanese guy. Had to turn fork preload adjusters pretty much all the way in to get close to proper sag (I am 210#). One turn on rear spring.

All I can say is that I was amazed at the improved handling in the twisties. For everyone with new Busa's this is a MUST DO.
 

JINKSTER

I Love my Wife!
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Nice write up Bill. Thanks for the tips.

I finally got around to tuning the suspension in my 2mo old Busa last rainy weekend. Same deal- factory settings appropriate for your average 140lb Japanese guy. Had to turn fork preload adjusters pretty much all the way in to get close to proper sag (I am 210#). One turn on rear spring.

All I can say is that I was amazed at the improved handling in the twisties. For everyone with new Busa's this is a MUST DO.
Thanks for the validation Cutter and yea man...pretty amazing dif for just tweaking in the stock hardware eh?..I was tooling around earlier today (running down to the local HD palace to order up some buell footpegs) and smiled the whole way..especially in what few curves I hit and how insted of squating in the rear when I nailed it?...it just bolted forward under hard acceleration..and that diving in the front during hard braking is noticably decreased as well.

Ya know..when I first got this busa two months ago I was rather shocked at just how nimble it was for it's size...but as i became more familiar with it and got up in the mountains during the Busa Bash where I got to push it hard through some curves I found myself "Holding Back" a tad as it became sorta vague and wallowy feeling when pushed hard but...not anymore...and now I'm all jazzed up and can't wait to get these new stiffer fork springs in and installed so I can get things dialed in spot on.

L8R, Bill
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Wayneswa

Registered
Thanks Jinkster. I'm on it now. It's 82 deg and sunny, must have it done soon so I can check it out. I'll post the results later.
Wayne
 




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