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budget 2002 sv650 cafe racer

This is a discussion on budget 2002 sv650 cafe racer within the Project Builds forums, part of the Caferacer.net Forums category; Originally Posted by jcw Having been there, I'll bet eventually you'll hit a bump that will make that rear tire contact the rear fender. Remember ...

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Thread: budget 2002 sv650 cafe racer

  1. #31
    Junior Member gt alex's Avatar
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    Quote Originally Posted by jcw View Post
    Having been there, I'll bet eventually you'll hit a bump that will make that rear tire contact the rear fender. Remember the rear tire will extend a little as it compresses.
    Nice looking bike, though! I'd ride it!
    It has 4 1/2 inches of travel and a fully adjustable shock and a spring slightly harder than stock that seems to match my weight requirments. I havn't adjusted the bump rubber height yet. I know i should and I will, but my plan was to play with compressiion damping if it's getting to close to the fender at the monment it's only on 1 click and it feels well matched to the front, with no sign of hitting yet.
    Fingers crossed. Thanks for your feedback it is all wellcome

  2. #32
    Senior Member TrialsRider's Avatar
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    Compression dampening is a function of shock absorption (resistance to change)
    it is the spring that carries the weight and determines the ride height of the motorcycle.

    You won't be adjusting ride height and fender clearances by adjusting the shock absorber dampening settings, she don't work that way.

  3. #33
    Junior Member gt alex's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Compression dampening is a function of shock absorption (resistance to change)
    it is the spring that carries the weight and determines the ride height of the motorcycle.

    You won't be adjusting ride height and fender clearances by adjusting the shock absorber dampening settings, she don't work that way.
    The spring rate is spot on with correct sag both static and loaded. in that situation if the wheel is traveling to much on bumps the compression damping fine tunes that travel.
    So I was not suggesting this would change ride height or static fender clearance. That would be silly. thanks

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  5. #34
    Senior Member TrialsRider's Avatar
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    The bike has a linkage on the rear suspension,
    that makes adjusting the swingarm position super cheap and easy with no actual change to the shock or spring.

    ... I have no idea how one could know it is correct without riding it to see if it actually rides like a pogo-stick or follows the road bumps well, ymmv.
    best luck with your project

  6. #35
    Junior Member gt alex's Avatar
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    Quote Originally Posted by TrialsRider View Post
    The bike has a linkage on the rear suspension,
    that makes adjusting the swingarm position super cheap and easy with no actual change to the shock or spring.

    ... I have no idea how one could know it is correct without riding it to see if it actually rides like a pogo-stick or follows the road bumps well, ymmv.
    best luck with your project
    To check sping rate at the rear for a given application. with the rear wheel off the ground get a vertical measurment to a frame datum. the with someome holding the bike up with wheels on level ground remeasure and adjust preload so the sag from the full drop measurment is 1cm less, then still with help holding the bike get on with full gear in riding position and remeasure. if that measurment drops a futher 35mm +- 5mm the spring rate is suitable for performance street use. if it sags too much it is too soft and not enough too hard. on the front I normally go 25 bike sag and further 25 with rider and tune to taste fiddling with preload.
    pogoing is normaly a result of mismatched damping front/rear.
    Changing dogbone length raises or lowers the back with only small impack on spring rate from altered geometry and none on damping.
    It is a bit like cooking different cheffs have their own reciepes
    I would like to hear reciepes others use when setting up. it all helps

  7. #36
    jcw
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    Quote Originally Posted by gt alex View Post
    To check sping rate at the rear for a given application. with the rear wheel off the ground get a vertical measurment to a frame datum. the with someome holding the bike up with wheels on level ground remeasure and adjust preload so the sag from the full drop measurment is 1cm less, then still with help holding the bike get on with full gear in riding position and remeasure. if that measurment drops a futher 35mm +- 5mm the spring rate is suitable for performance street use. if it sags too much it is too soft and not enough too hard. on the front I normally go 25 bike sag and further 25 with rider and tune to taste fiddling with preload.
    pogoing is normaly a result of mismatched damping front/rear.
    Changing dogbone length raises or lowers the back with only small impack on spring rate from altered geometry and none on damping.
    It is a bit like cooking different cheffs have their own reciepes
    I would like to hear reciepes others use when setting up. it all helps
    Your free sag numbers are off.

    If your bike drops a whole 25mm on it's own weight, total rider sag will be according to your numbers 60-70mm in rear and 50mm in front. Typically rider plus bike sag measurements are 30-35mm on street and 20-25mm on track. At 6-7 cm, you will have used too much of your fork and shock travel and will bottom the suspension. Total fork travel on sv650 is 12cm but hydraulic lock with fork oil in place might even be a couple cm less.
    Setting sag means less on track where you set up a bike dynamically for what you need it to do on track rather than sitting still in pit lane.

    Pogoing I assume means the suspension oscillating through more than one cycle when it hits a bump. This is an issue with rebound adjustment.

    Changing dogbone length affects the effective spring rate by changing the angle of the shock to the frame. You can see this practically by noting the change in your sag when you change your dogbone length.


    Something tells me that this will mean nothing to you, though...
    Last edited by jcw; 11-14-2019 at 09:13 AM.

  8. #37
    Senior Member TrialsRider's Avatar
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    My BMW rides nice on the street, that has a tiny bit of spring sag even with my uber lightweight ass on it, mostly because the thing is fitted with progressive rate springs designed to provide some rider comfort on little bumps. (bike is definitely not a high performance suspension setup) My MV Agusta by sharp contrast is all about performance and screw the comfort, constant rate springs, stiff as shit in the rear, the only way I can make the rear suspension actually work as it is designed to do is to ride it very illegal like (high speed and frequently on the rear wheel only, it thrives on that kind of riding) My trials bikes are dead easy to suspension test and adjust :/ just ride up and down a few 4 foot vertical rock faces, the spring rates, tire pressures and shock settings become immediately apparent. Performance street use? Not sure what that even is, imho it's either a great performance bike, a great street bike, or a bike that has been performance compromised.

  9. #38
    jcw
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    I've been chasing suspension settings and monitoring tire wear at the track this year. I've exhausted a lot of mental energy contemplating the topics of geometry and springs and suspension and the role they play in motorcycle dynamics.

    As far as spring rates, my little synopsis is this...

    Springs function to 1) support the bike and its rider 2) absorb some of the forces that are applied to the tire and wheels (ie bumps) 3) maintain the tires' contact with the ground for traction.

    Without going into extensive discussion, softer springs that are set with enough preload will accomplish the above effectively. There is a youtube channel Engineering Explained I believe that has an video that explains why softer springs are actually better at maintaining tire contact with the ground than stiffer springs.The video pertains to cars but the same explanation can be applied to bikes in this example.

    So, why then are track bikes sprung so stiff?
    The simple reason is that in a corner or braking or accelerating, load is put on the front or back or both suspensions that a softer spring is unable to support the bike and rider while maintaining adequate suspension travel. For example, imagine a race bike cornering at 45-50 deg lean angle and around 1.0g load. the springs are now loaded with twice the sprung weight of the motorcycle and rider. Can that be an additional 500 pounds? Maybe, I don't know the math enough to be sure. But it is a significant amount of additional weight compressing the springs. This requires a higher spring rate to keep the suspension from bottoming out if it encounters a bump while compressed.
    It is not uncommon for a 140 pound professional rider needing a spring stiffer than a 200 pound weekend trackday rider. The reason all comes down to how hard they ride the bike.
    This is the reason why one "correct" spring rate for a racing motorcycle is a fallacy. Many times, there will be different "correct" spring rates for different tracks depending on the amount of braking, accelerating and the types of corners present.

    By setting preload, you can fine tune the chassis in a corner by adjusting the ride heights front and rear so that the bike will either be more stable or more responsive. This fine tuning of preload is way more important on track than what free and rider sag is when the bike is sitting in the pits.

    In contrast, a street rider cornering at 20-30deg lean and modest braking levels won't need the heavy stiff springs that a racer might and would actually benefit from a comfort and safety standpoint with a softer spring as long as ride height is maintained.
    Last edited by jcw; 11-14-2019 at 10:27 PM.
    woodsman likes this.

  10. #39
    Junior Member gt alex's Avatar
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    Quote Originally Posted by jcw View Post
    Your free sag numbers are off....
    True I agree I knew I had made that error straight after submitting it but it was 1AM and too late to bother changing it. On the bright side it did open up discussion.
    it sounds like we are starting to speak the same lingo.

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