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Stupid suspension question: some help needed.

Discussion in 'The Garage' started by vaquero, Jan 13, 2020.

  1. vaquero

    vaquero XS650 Member

    Ok, first things first, thank you all ya'll for just being here!!

    I have been going round with this one, so here's the long version:
    I am in the middle of a complete build- my first- something probably in the middle of a brat and a tracker, but kinda Euro too. Narrow Avon MK series tires, etc.. It will have a remote master cylinder under the tank so I don't have to have a reservoir on the bars. Simple aesthetic, not a racer. I am running an 18" rear wheel (mag) from an SR500 and then the 19" mag up front.
    The motor is out. I have cut off the rear end and fab'd up a new hoop. I just finished new upper shock mounts and have those in. I have been talking with Jeff in the custom shock department at Racetech, who is awesome by the way. He's got me lined out on all the particulars for clearances, sag, and all that meow meow. What I need is some advice on how to mock it up so it sits and handles right in the end. Am I supposed to make the top horizontal tube on the sub-frame actually sit dead level? That line would then mirror the bottom of the gas tank and also in theory the bottom of the seat (just saying, pretty parallel anyway, maybe not exact). Or do I go by the lower frame members under the engine? OR I could look up the stock head tube angle and set up the whole frame so that mics out right, in it's lowered stance? The new look will be a little lower than stock, but not a ton (and really maybe not at all with the 18" rear wheel, just looks like it). I have the forks sticking out of the top triple clamp 5/8" or so (like that aesthetic) and now have the top tube of the sub-frame at level. IF this is the desired outcome, do I jack it up in the rear 25% so when the bike is under sag it sits back down to where it is now? I will need these measurements when I order up the custom G3 shocks from Racetech. For now, I'll fab up some rigid stays that will keep the bike at the desired height until I can get all the stuff back on the bike and weight it.

    Thanks for any advice!!
     
    59Tebo, gggGary and Jim like this.
  2. Jim

    Jim Beyond the edge, is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Can't answer your questions but here's some frame drawings that gives you a good idea of horizontal reference. Good luck.

    framespecial.jpg

    framestandard.jpg

    framexs-2.jpg
     
    zodc, RC4MAN, 59Tebo and 3 others like this.
  3. Ratranger

    Ratranger XS650 Junkie Top Contributor

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    I would go by fork angle. I have mine at 25* and some change, rougher roads at 60 and above it feels twitchy. So I would aim for between 26 and 27* of rake. That should hande real well without being twitchy or feeling unstable.
     
    Jim, 59Tebo, Raymondo and 1 other person like this.
  4. Signal

    Signal XS650 Junkie Top Contributor

    I agree with Ratranger, Grizld1 has a good thread on here with suspension set up pointers on it.
    The 18 inch rear will quicken up the steering a bit by changing the steering head angle and reducing the trail.
    To check assemble the rear end and chock up the lower frame rails until you get the desired steering head angle.
    Well that how I would do it but others may have better methods.
     
    Jim, 59Tebo and Raymondo like this.
  5. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Madness is low in front and a "bit high in the rear" has good to excellent road manners EXCEPT with 30, 35 pounds of weight in the saddlebags and a tail bag, it will get a bit "weave happy" at 75 plus MPH. a good grip on the bars is enough to keep it straight but it could go into a tank slapper if left unchecked. Without the weight on the back, no issues, won't weave even if I upset the bars on purpose.
    Full disclosure; wide 18" rims and low profile tires front and rear. quality rear shocks, stiffer fork springs and damping.
    This is pretty normal stuff, get the steering precise and "flickable" and pay a bit in stability. Especially with these vintage flexy frames.
    Would weave at speed.
    20180614_094916.jpg
    No issues, pic the morning I did an iron butt on it.
    20190722_074107.jpg
    straight on pic for "stance".
    DSCN3213.JPG
     
    Jim, lakeview and 59Tebo like this.
  6. 59Tebo

    59Tebo 59Tebo Top Contributor

    Sounds intriguing. Pictures? Sketches? (Even if you doodle on the frame drawings sent by Jim...)
     
    Jim and gggGary like this.
  7. vaquero

    vaquero XS650 Member


    THX for these drawings Jim. That helps a lot. Sounds like Ratranger1 found his bike close to stock in the end. I'll also work on uploading some pics.
     
    Jim likes this.
  8. vaquero

    vaquero XS650 Member

    Man I love forums. I'll do a diameter check of the old 16" wheel vs the new 18" for giggles, but the head tube as it sits is 26.7* with the top tube of the subframe at dead level, so just under the published stock 27* (based on Jim's drawings). And if Ratranger's suspicions are correct that his 25* is too steep and I should shoot between 26-27*, then it's money the way it is. Ratranger, are you using stock forks? It's sitting at 13-9/16" for a shock length, which is quite a bit higher than stock, but part of that is the change in location of the shock mounts themselves- they are tighter to the subframe.

    I guess this means that I take this as the desired ride height and add my desired SAG to the shock length as it sits. RAD!! This gives me a direction to move forward. I'm sure there is some compression (static sag) happening up front as the bike sits, but without the motor it's gotta be negligible. Thanks ya'll!
     
    Jim likes this.
  9. vaquero

    vaquero XS650 Member

    Here is a shot of the bike on the stand, and a shot of the new upper shock mounts. Hoop came out well I think.
     

    Attached Files:

  10. 59Tebo

    59Tebo 59Tebo Top Contributor

    That's pretty cool, vaquero. It looks like you've got a great start to your project. This is kinda what I'm going for:
    Redefine-XS650-Frame - Copy.jpg
    This is not mine (Redefine Cycles Xs650), but the seat loop will be similar, and the stretched swing arm will give it the lines of a rigid, while retaining a rear suspension. Bulletins when they happen. I've got a long, long way to go, and with my budget (what budget?) don't anybody hold their breath! :doh:
     
    Jim and gggGary like this.
  11. Ratranger

    Ratranger XS650 Junkie Top Contributor

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    I'm not using stock suspension at all. Mine has zx6r forks and a monoshock. I would say it looks like you are off to a good start.
     
    gggGary likes this.
  12. vaquero

    vaquero XS650 Member

    59Tebo, you have your work cut out for you. I'll look forward to seeing you pull that off.

    Ratranger, did you ever map out the offset #'s on the stock vs ZX6R forks? I've seen some of the parts Cognito Moto sells and that whole front end swap is so tempting... I live in a small town and would love to just find some forks like that locally. I keep looking.
     
    gggGary likes this.
  13. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Last edited: Jan 15, 2020
    Raymondo and 59Tebo like this.
  14. 5twins

    5twins XS650 Guru Top Contributor

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    You may have issues with the SR500 rear wheel. I don't think it will allow a small enough sprocket to be installed.
     
  15. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    :agree: I have one here, think it's sr 500 that's the smallest sprocket to fit that bolt ring, 42 tooth :poo:
    wheels 017.JPG wheels 016.JPG
     
    59Tebo likes this.
  16. vaquero

    vaquero XS650 Member

    I had one custom made. Easy and not too pricey. Send them the bolt pattern and the center hole diameter and they can do whatever hole pattern you want. I got a 32 tooth. I did some math on the whole thing a while back when I got the wheel. Its also for a 520 chain so I can take some weight off.
     
    gggGary likes this.
  17. vaquero

    vaquero XS650 Member

    While were at it, what rims do XS owners like? Lets narrow that down to the cafe and tracker crowd. Chop guys will have way different sizes and needs. I would be interested in 18 rear, 19 front. Excel vs Warp 9 vs Sun?
     
  18. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

  19. vaquero

    vaquero XS650 Member

    Nnnnice gggGARY! I love those rims. They have such an English vibe. I've heard about the spoke angle thing. Adds an air of intimidation. Are those the upgraded EBC rotors from Leo at 650 Central?
     
    Jim likes this.
  20. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    They push all my buttons, I bought 4 or 5 at time directly from the italian vender bypassing fee-bay. .
    CIRCLE BORDER WITH TYPE BORRANI RECORD ALUMINUM WM3 2,15x18 36 HOLES link is a narrower rim, but that's the guy.
    Old FZR600 rotors off fleabay. work great, about 7mm spacers tween rotors n hub. I made a cheesy spoke angle recutting tool have used it on 4 or 5 rims and put a lot of miles on a few of them. Madness ahs about 9K since these rims were fitted. That wide 18 front makes for tricky caliper install, remove, it's like a chinese puzzle. Finally found it easiest to remove the rotor bolts BEFORE taking off the calipers. LOL.
     
    Last edited: Jan 17, 2020
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