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1983 V45 Sabre Cafe Racer

This is a discussion on 1983 V45 Sabre Cafe Racer within the Project Builds forums, part of the Caferacer.net Forums category; 27.5 degrees 3.98 inches 23.6 degrees 3.8 inches 23 degrees 2.48 inches Those are for my bikes BMW, MV and Montesa, note the MV has ...

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Thread: 1983 V45 Sabre Cafe Racer

  1. #81
    Senior Member TrialsRider's Avatar
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    27.5 degrees 3.98 inches
    23.6 degrees 3.8 inches
    23 degrees 2.48 inches

    Those are for my bikes BMW, MV and Montesa, note the MV has almost the same as the trials bike, those bikes are both kick ass responsive as the numbers would imply,
    the beemer is a sport touring bike, handling is perfect suited to the autobahn but limited to period design tires just like your bike.


    ... shortening a suspensions travel on a road bike is completely contrary to a motorcycles safe handling, performance wise it's just dumb if you're planning to give a fast motorcycle about the same usable suspension travel as a honda 90 step through, makes no sense unless you're going to ride it at scooter speed.
    + no way an informed motorcycle mechanic is going to sign off on that modification, you need to find one that doesn't have a clue :|

    Hey, you want to try a trials bike? that would be good for a laugh
    Last edited by TrialsRider; 10-26-2018 at 05:35 PM. Reason: we could take pictures of you crashing and post them on here.

  2. #82
    Member BalkanMoto's Avatar
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    alright I measured everything out more precisely. Accommodated for the grade on my driveway as well. Here is the numbers:

    Rake: 27.2°
    Tire Radius: 25.795" (110/90/R18)
    Triple Clamp Offset: 2.375"
    Fork Length: 29" 3/4

    Using the https://www.rbracing-rsr.com/rakeandtrail.html calculator that leave:

    Trail:3.96"

    Me being not so trusting of random calculators online, I did pull out my trusty laser meter and double checked that the trail is indeed ~4.0".

    Also played around with the fork to see how much travel it actually has rough measurement is 3" (which is consistent with what everyone is saying would happen)

    Now where all that leave me, is essentially with a front end that should be about as stable as the above mentioned BMW example by TrialsRider. With about 3" of travel, and not the stiffest of springs. Certainly not a knee dropping, corner carving with confidence, beast of a machine. But also not an unstable death trap.

    Now I would like to hear people's opinion of what the handling characteristics of a machine with roughly the specs above? (I would like to hear the actual technical aspects not just "its shit" type answers.)

    Also the forks currently sit 2" above the top yoke. Since I am planning on putting clip-ons, that does leave me with that room of adjust-ability. So given that currently is how the forks were originally mounted, i could slide the forks down and have them "flush" with the yoke. Which would put the rake and fork length roughly at the stock amount, minus the travel of course. Either way there is options.

    What is people's opinion of those steering dampeners? (not sure what they are actually called, the little mini hydraulic actuator that connects to the fork and make the turning action much smoother and gradual.)
    Last edited by BalkanMoto; 10-27-2018 at 11:47 AM.
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  3. #83
    Senior Member 8ball's Avatar
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    When you calculated fork length, did you subtract the 2" that are sticking up above the triple clamp?

    How much of the 3" of travel are going to be taken up by the sag with you and the weight of the bike on it?Usually, you would set up the sag to be between 1" to 1.5"......so now how much travel do you think you have?

    Also remember, that trail decreases when the fork compresses....like when you hit the brakes, or hit a bump, or sit on the bike. So when Granny pulls her Buick out in front of you and you hit the brakes, if you are bottomed out with no suspension give, and your trail goes to the region of shopping cart wheel...... that is NOT a good time to discover how unstable the front end is.
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  5. #84
    Member BalkanMoto's Avatar
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    Yes the fork length is measured from the top of the top yoke to the center of the front wheel axle. (aka. excluding the top 2"). I agree with all that you have pointed out about the forks characteristics under static load, and heavy breaking.

  6. #85
    Senior Member TrialsRider's Avatar
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    Sounds like the axle is offset forward on the fork leg and that is messing up your measurements.
    What's the rake angle measured at the steering head,
    what's the trail using a line through the steering head bearing to the ground and then from that to the bottom of the tire contact patch?

  7. #86
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by BalkanMoto View Post
    .. I agree with all that you have pointed out about the forks characteristics under static load, and heavy breaking.
    add:
    Compression through corners, reaction to bumps, resistance to head shake (rigidity of the entire assembly), steering dampener is a nice add on.

  8. #87
    Senior Member kenessex's Avatar
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    OK Sparky,
    Here is a reasonable suggestion for you. Given that you don't have enough experience to make any reasonable assumptions and that you have been given plenty of advice on here that ranges from very wrong to maybe right based on their assumptions, here is what you have to do. Return your forks to stock with the appropriate amount of appropriate oil in them and put them in the stock location.. Then once you get the bike up and running, ride it a while and make the adjustments as needed. Right now, you don't know what to do. Based on my experience, what you have now is a recipe for disaster with respect to handling, compliance and ground clearance.
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  9. #88
    Senior Member brad black's Avatar
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    it's going to bottom out hard and often. when it does, the only suspension you have left is the tyre. hitting bumps under braking is when it will be most unstable, and it'll probably bounce off bumps as there's no suspension left.

    get a big piece of steel, put it on the concrete and hit it hard with a hammer. that's what it sounds and feels like, and if you have mechanical sympathy, it'll make your skin crawl.
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  10. #89
    Senior Member brad black's Avatar
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    so, if we say it only has 80mm of travel, you'll need a 0.9kg.mm spring.

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  11. #90
    Senior Member TrialsRider's Avatar
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    once you run out of suspension travel bad things happen, the rider becomes the crumple zone right along with the motorcycle:

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