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Need help with the NT650 Hawk suspension geometry:Bike Finished!

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    Need help with the NT650 Hawk suspension geometry:Bike Finished!

    Hello everyone! I posted this in the "New Member" forum, but thought I could post here too. Need some help!!

    I am doing a cafe rebuild on a 1982 Honda CM450, but am utilizing the Hawk's single swing arm. The conversion has been interesting and challenging to say the least! I am done with welding in the larger pivot housing for the single swing arm that accommodates the 15mm pivot shaft (instead of 14mm). Right now, I am stuck on the top mount for the rear monoshock conversion. In order to place this mount in the best position on the frame, I need to know the best swing arm angle (from horizontal) to get the most optimum anti-squat angle, and thus anti-squat.

    I have been reading through "Race Tech's Motorcycle Suspension Bible" specifically chapter 5, and also this very good article... http://www.sportrider.com/tech/146_0...tion_geometry/

    I am looking for someone with a NT650 Hawk that can measure some rear suspension distances and angles for me? I will only need a couple things and the info will be most valuable for this rebuild. Thank you!

    Here is my build thread...
    http://www.hondatwins.net/forum/view...p?f=61&t=28042

    Later,
    Jared

    #2
    We'll get you the #'s,no problem.However(always a but),do you realize the springrates you're dealing with in stock hawk geometry? A 1100-1300 lb spring may stress the old steel frame more than you realize.That'll need to be a beefy top mount,and that being said,you'll be getting a lot more frame flex from the sssa.I'll give you the one measurement we don't have off the top of my head -you've got the swinger-the shock can be from 310 to 325 eye to eye centers.I'll give you the orientation of the topmount from the pivot.

    Comment


      #3
      Not sure if you are aware, but after looking through your build thread on hondatwins.net keep in mind that the Hawk does not use a linkage type suspension like the R6 shock you seem to be using on your build.
      John Hawk GT's 88, 2-89's, 90

      Comment


      • behindthetimes
        behindthetimes commented
        Editing a comment
        R6 shock.....that's a wet noodle- like a 500lb spring.I wonder ...do you know anything about suspension valving?Spring rates?BTW- if you really ARE using an R6 shock.....I got a nice WP with several springs .....came off one of the old superbike race builds.It's the 2001-2003 spec shock.

      #4
      Who cares about suspension numbers when someone cobbles up a fashion-following showpiece like that ? It's all about style, not engineering, innit ??
      Last edited by squirrelman; 01-31-2014, 08:19 PM.
      "It's only getting worse."


      MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

      Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

      Comment


      • ParcNHawk
        ParcNHawk commented
        Editing a comment
        Every time I see one of these bikes I think "what could I have done to stop it."

      #5
      Squirrelman got you covered - for this kind of work, make it like you want it to look, then see what it does and take it from there...

      Comment


      • behindthetimes
        behindthetimes commented
        Editing a comment
        See! Hord actually GETS it too.Every subtle nuance.JanM is a Suspension Meister,Jared. He can make any suspension work.

      • Hordpower
        Hordpower commented
        Editing a comment
        I think of it as channeling Lenac.

      • behindthetimes
        behindthetimes commented
        Editing a comment
        BAWHAWHAWHAWHAW! You Fuckin guyz.....

      #6
      BTT.. Iam all over what you are saying about that CM noodle-pasta frame and the massive loads that a SSSA will put on it..Look at the moynt point of the SSSA on the Hawk..As you so aptly noted, a 1200 pound spring would really load up the pivot mount...The Hawk has massive extruded alloy spars and a robust pivot mount for the SSSA..The CM has Nothing..I would rethink to entire build,jaredc7..have an engineer do some stress analysis for you then decide how to build a bulkhead capable of surviving the massive loads a SSSA will impart on the mount area before looking at angles of dangles or something..just saying.. and I am an engineer...I will never say Don't Do It, but I would look at the stress analysis and go from there..
      If mice were men and men were mice, once upon a time, Men were mice and mice were men, twice upon a time.

      Comment


      • F14
        F14 commented
        Editing a comment
        And Zym has a LOT of experience in mc framinology!

      • jaredc7
        jaredc7 commented
        Editing a comment
        Thanks for the thoughts Zymm! I'll be sure to do my homework with the forces at work here on the SSA pivot and the shock top mount. I'll let you know how it turns out.

      #7
      Ok ,enough of the scathing skepticism! Here's what I got.........center to center from the swinger pivot to topmount approx. 260mm.....orientation ..topmount approx. 25mm forward of pivot.That's the last leg of the triangle.You'll be able to figure it out from that.Bolt the sssa and shock in( a shock 310-325 long-not the R6)and locate the top mount 260mm up from the pivot.The top position will locate itself.Capish?

      Comment


        #8
        Seems to me that you all are working on the premise that both the CM450 and NT650 in their own are ideal bikes and it is necessary to maintain either original setup or implement known good upgrades - neither can be right at the same time, right?

        Jared, you are just looking at suspension, it is more like basic construction when adding swingarm and shock as I see it, so I would recommend reading and working with John Bradley's "The racing motorcycle - a technical guide for constructors", vol. 1 and 2. Then model and work with your preferred visual design in Tony Foale's Motorcycle Setup Analysis software to evaluate performance of your choices. You also need to do something with the R6 shock you have, at least a new spring and preferably also modify internal setup. And when all is done you need to setup the whole bike, expect to make changes to springs front and rear as well as damping front and rear...

        I really do not see a big risk for a squat problem with a CM450 base, I would imagine a lot of unwanted frame flex from upgraded forks, brakes, tires and new shock/rearend layout. But maybe you also have big plans for the powerplant?

        Should I do something like this, I would have visual appearance as 1st priority, then build it erring on overdimensioning of your changes. Ride it, see how you like it, then rebuild or adjust...

        Comment


        • behindthetimes
          behindthetimes commented
          Editing a comment
          All of us Jan?? ALLLLLLL of us? I'm shattered....devastated.....at least I answered the question from the OP.:willy:


          Actually ,I'm w/u. Go ahead .Build it.What's the worst that could happen?

        • JanM
          JanM commented
          Editing a comment
          Yeah, the "you all" wording came out a little wrong - all of us are saying basically the same as I see it.

          If Jared wants to build it then go for it - just try to be a little realistic on the outcome..

        #9
        The more you actually KNOW about it,the more leery you get of creating new designs w/o knowing the stresses and loads.I'm an adventurous builder but my biggest concerns are always handling.I know If I start changing things from a known set-up ,that to get it RIGHT will cost time and $$.Worth it to take it to a shock dyno.But we're nuts.If you're cobbling together something like a 450 twin Honda....doesn't matter.It's gonna be slow.It's not a racebike...it'll be fun and unusual.We want pics when it's done!

        Comment


          #10
          Thank you all for the responses! There is a lot here to go through, but definitely glad to hear from everyone.

          I might start off by saying that it is obvious I could have just bought a motorcycle, or maybe started with one that made these modifications a little less challenging. For me, the point of all this was more-so to have a project with many challenges for my engineering mind and my tinkering hands. Having a motorcycle at the end is a bonus. It is the challenge and the problems that I get to figure out that drives me!

          Thanks to OldTimer for the vote of confidence and offering your help with some details. For the life of me, I cannot find the stock spring rate of my CM450, and Iíve checked everything I can think of. Plan B - The Yamaha R6 shock is 547 lb/in, which is very close to the recommended spring rate for my bike (roughly 450 lbs wet weight & after all new parts are on) and a rider of my weight (175 including gear). Unfortunately, I can't find the website I used to check this spring rate selection originally, but there are quite a few others out there, and they all agree. If I need to get a stiffer rear shock, that's no biggie. The Yamaha shock was about $40. If I do HAVE to have a stiffer spring that can still be used with the R6 shock, then I would be interested in your springs, OldTimer! Maybe I it would be better to just find another monoshock thatís about 700 lb/in to 800 lb/in? The Hawkís 1100 lb/in seems like way too much.

          As for the rear shock top mount, I analyzed these stresses with an engineer buddy who has a masterís degree and 8 yearsí experience in steel stress analysis. Our conclusion, after a few pages of calcs, was that a 1/4" thick steel shock top mount would be enough to allow the admittedly "noodle-like" frame of the CM450 ​to resist "punching-through" forces. Also, a quantity of three 1-inch stitch welds for each side would be enough to sufficiently transfer the forces into the lateral (strong-axis) part of the frame. The next part is to do some analysis for the pivot of the SSA. I gave it every bit of strengthening that made sense, aside from welding on steel plates on the sides of the frame around the pivot shaft. Any thoughts on that?

          Zymmer4 Ė I understand your concerns on the loads transferred by the SSA. Here is a build thread for another guy who has done a similar monoshock conversion on an old Honda like mine. Not to say that since this other guy did it, everything should be ok, but it is at least an interesting thread. He is using the Yamaha R6 shock as well. Let me know what you think! viewtopic.php?f=5&t=19259

          OldTimer Ė Thank you for the details from the Hawk swingarm. Iíll be using those numbers to dry-fit everything together, double-check all the dimensions and angles, and then weld the top mount in.

          JanM Ė Thanks for the reference on John Bradleyís book, and Tony Foaleís software. Iíll definitely be incorporating those into my design. Race Techís Suspension Bible has been some help, but the section on suspension dynamics and design in only about 8 pages. I am being realistic on the outcomeÖ I donít expect this to be the perfect bike to rip up and down mountain twisties. The manufacturers have a much better bike than Iíll ever custom build like this.

          Like OldTimer said, I am looking forward to having something fun and unsual! If I wanted a fast bike, I wouldnít have started with a 450

          Thanks again to everyone, and Iíll keep you posted on the progress. Iím sure there are plenty of legitimate concerns, but itís my goal to prove people like ParcNHawk wrong

          Comment


          • behindthetimes
            behindthetimes commented
            Editing a comment
            Good! That being said- I'm not sure your grasp of suspension geometry and relative spring rates is up to speed,so to speak.If you re-create accurate Hawk geometry on your project it will REQUIRE a 1100 lb spring to feel like a STOCK HAWK>it'll be SOFT. It's not about the spring rate,it's about leverage and mechanical advantage.A 600lb spring on a Hawk would bottom out from just a rider.I'm sure you'll be able to get a stock Hawk shock to try.Now...Carry on!

          • jaredc7
            jaredc7 commented
            Editing a comment
            I understand... seems like the 1100 lb/in spring rate is a harsh reality I need to come to terms with. How then do I reconcile the recommended spring rates from websites like racetech.com and sonicsprings.com? Is it because the other bikes use a linkage system and the Hawk 650 is directly mounted between the swingarm and frame?

            I was able to find a chart of sport bike spring rates (see link below), and found a few OEM shocks that fit my budget a lot better than buying an aftermarket shock (read penske, ohlins, yss, wilbers, hyperpro, etc. etc.) The only two late model (thus low mileage) bikes that provide lost of purchase options on eBay are the Honda VFR750/VFR800 (7" stroke & 1100-1200 lb/in) and the Kawasaki EX650 (5" stroke & 1200 lb/in). None of the other bikes had reasonable prices or enough options to get a quality low-mileage shock.

            http://www.reactivesuspension.com/do...TION_CHART.pdf

          #11
          Someone here will have a stock Hawk shock...YES- the linkages on some bike reduce the spring rate required through a lever system that divides the load.The direct mounting of the Hawk shock give the SSSA a tremendous mechanical advantage-think of it as a piece of pipe on the end of a breaker- bar the longer the lever,the greater the MA.

          Comment


          • jaredc7
            jaredc7 commented
            Editing a comment
            Looks like ancient rider has a decent looking Hawk shock for sale. I PM'd him for some details.

            Just to consider all my options though, is the VFR750/800 rear shock a good one? The spring rate is 1000 lb/in and the stroke is 7" as opposed to the Hawks 1100 and 6". The increase in length would make the shock more vertical (with the same swingarm angle). Is it true that a more vertical shock won't ride as good as one that is setup more horizontally? On the other hand, the VFR shock would give a lower horizontal force into the CM450 frame, which seems to be an advantage. The only other economical option is the Kawasaki EX650, which has the same spring rate as the Hawk, but is only 5" in length. Thoughts?

          • melmsrt4
            melmsrt4 commented
            Editing a comment
            No intent to discredit ancient rider, but stock Hawk shocks are junk, no matter how little miles they have or how good they look. Only good for holding the bike up in the garage or a starting point for reference measurements. Others have tried to use shocks from other bikes with mixed results, mostly negative, with the exception of the 900rr shock that has been revalved. Without revalving, other shocks will not work. If you have gone through all this trouble on the frame and swingarm, don't skimp on the shock. Just get an aftermarket Hawk shock from Hord and be done. My two cents. GL

          #12
          J.D. Hord
          Keeper of Engine Nomenclature, 9th Order

          Comment


            #13
            "because I can..."

            Comment


            • Hordpower
              Hordpower commented
              Editing a comment
              Absolutely.

            #14
            Your #s for shock stroke are the numbers for actual suspension "travel" not stroke.A hawk shock only had about 50mm of stroke , a VFR maybe 65mm.... Now for your next lesson-
            Shock Length- Eye/to/eye measurements-like the first # I gave you of 310mm(stock Hawk) differs from bike model to bike model-If you find the actual measurement from a VFR or a Kawi EX650 you're gonna find you were completely wrong about their length and compatibility with your build.Travel is measured at the rear axle,while stroke is how far the shock actually compresses.When you multiply the stroke by the length of the swingarm,50mm at the shock turns into 6" at the spindle. Understand.?Even a shock that listed as having the proper stroke can be totally wrong in length.

            Comment


              #15
              Nah, I think Jared is confusing spring free length and stroke. Looks to me that Jared needs to do some more investigation on what he is working with. Asking on forums is one thing and you can get a lot of help, but you need to be able to sort the info and get your own grasp on these things, Jared. There is a lot of incorrect info out there (eg. do not uncritically use info from the Racetech website) and if you ask imprecise questions or questions based on incorrect assumptions, the answer is probably not fulfilling...

              behindthetimes is a great resource and has made similar big changes to bikes, so take note of his comments.

              Comment


              • behindthetimes
                behindthetimes commented
                Editing a comment
                Why thank you Jan.You know I've great respect for you as well.There are definitely things that I ask you! Jared,you're getting Global Advice,from Germany to Ohio,to West V to Ct. Engineers/Builders/Racers all.
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