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  1. #1

    Default Determining swing arm width

    alright guys im still new to the building side of things so take it easy on me here. I'm going to start my first build this weekend and have everything all figured out besides one thing. i need to figure out how to determine how wide to make the swing arm. i would like to put a high 200's low 300's on the rear. if you could be so kind as to give some words of wisdom i would greatly appreciate it
    Last edited by LisaBallard; 10-31-2018 at 9:57 AM.

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    For a first build you are biting off a big chunk. Almost overwhelming depending on your past experience.

    You need to tell us the style of the motorcycle or where and how it would be used.

    I would use a 200mm rear tire or smaller. If you go any larger the bike may not handle very well. A 300mm rear tire would be for a custom bike or show bike.
    A chopper style bike? Some other custom build.

    I have ridden a bike with a 240mm rear tire and skinny front tire and if you pull off of the road on a downslope the dynamics of the tires want to pull the bike down hill. Trying to get back up onto the road is difficult. Thats what I know for sure.

    For the width of the swing arm I would look at stock bikes that are sold with 200mm rear tires and go from there.
    The width of the front of the swing arm is determined by the frame and engine design.

    The rear of the swing arm is determined by the wheel width, brake caliper and rotor thickness and the width of the sprocket and spacers needed.
    You need to know if you will use a chain or belt drive.

    There are wide swing arms sold for some stock bikes. They are not cheap. The design work is done for you.

    Lots of other considerations too.
    Last edited by Luky; 10-31-2018 at 9:12 AM.

  3. #3

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    lucky, yeah its a lot to take on but hey you gotta start somewhere. the motors and trans aspect isnt a problem as ive been working this type of stuff for quite some time. im wanting to go after a rigid breakout style using a '99 88c.i. harley motor

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    also the bike will be used as a go for a cruise bike. maybe some shows

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    Quote Originally Posted by dkapp0802 View Post
    i would like to put a high 200's low 300's on the rear. if you could be so kind as to give some words of wisdom i would greatly appreciate it
    Don't do it..... That's my nickle....

    If the bike is running right now ride it and enjoy it....

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    Pointing out the obvious...
    You want to run a beach ball on the back you will need to use right hand drive.

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    EDIT:
    You said "swingarm" and "rigid breakout style". WHICH IS IT? Please use correct terms!

    If swingarm:

    I'd copy existing wide tire kits of the size you desire which fit whatever transmission and frame you intend to use. No point in reinventing the wheel and plenty of point in saving a ton of cash. Some instruction sheets with photos to give you ideas. https://heartlandbiker.com/pages/frontpage

    Assemble your rear wheel/brake/washers/spacers/axle adjusters/etc including two lengths of the tubing you'll use for the swingarm. You can't get that wrong because the parts located the tubing. Square up the tubing, tack weld, verify squareness, finish swingarm except for the pivot.

    Align the swingarm wheel/tubing assembly with the swingarm pivot. Tack and verify all is square and correct. Finish weld checking for squareness as you go since (I don't know how much you weld, no insult intended!) weldments can and do pull out of shape. Control with clamps etc on a flat surface. Digital levels are very useful.

    If rigid, do similar but with axle plates instead of swingarm tubing to get your desire rear frame width.

    A more detailed description of your project with pics would REALLY help others help you.
    Last edited by farmall; 10-31-2018 at 3:25 PM.

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    Quote Originally Posted by dkapp0802 View Post
    lucky, yeah its a lot to take on but hey you gotta start somewhere. the motors and trans aspect isnt a problem as ive been working this type of stuff for quite some time. im wanting to go after a rigid breakout style using a '99 88c.i. harley motor
    A "rigid breakout style" What does that mean? Do you bean a rigid frame motorcycle?

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    "rigid breakout" is a dealer label for a rubber mount Evo sportster right?
    Kinda like dudes that say they have a "48" and it turns out to be an Fi sportster, whomp whaaaaa

    Anyway, why you wanna weigh down an already anemic 883 with a big, heavy, fat tire?
    And if you go full retard with a 300, your gonna need a jackshaft... I.e. lots of fabrication.
    Even with a "kit"

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    No, he said 88" Breakout:

    2014 Harley-Davidson® FXSB Breakout®
    Click image for larger version. 

Name:	img_UlvWnpUG6nFYi4X.jpg 
Views:	3 
Size:	270.2 KB 
ID:	88502
    https://www.smartcycleguide.com/L52509570

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    I stand corrected
    At least I was right about him hanging out at the dealer too much lol.
    To each his own, but I see the above cycle more dangerous than not running a front brake.

    Don't drink the MoCo Kool aid!!!

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    Quote Originally Posted by Sky View Post
    "rigid breakout" is a dealer label for a rubber mount Evo sportster right?
    Kinda like dudes that say they have a "48" and it turns out to be an Fi sportster, whomp whaaaaa

    Like people saying they have an iron..... WTF

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    This section should get him sorted out:

    https://www.chopperhandbook.com/widetire.htm

    Before you undertake a wide tire project it is, in my opinion, essential that you have the wheel, tire, sprocket or pulley and fender for your particular project in the shop so you can make real measurements of the components you're going to use. This is the only way you're going to be able to make a 'tight' frame.

    Most aftermarket mass-produced wide tire frames are built to 'maximum' dimensions that take into consideration the 'worse-case' scenario of a combination of components and this is why you sometimes see as much as two inches of 'air-space' between the frame rails and the sides of the fender on some bikes. Our objective is to build a frame that fits the components perfectly to create a nice 'tight' fit between the rails and the other component parts.

    Before we go much further it should be understood that building a nice wide tire frame is as much art as it is technicalities and no two builders will produce the same frame even if they're both using the same set of design dimensions. These are not the type of frames to make your break-in to frame building on and I urge the first time fabricator to build a couple of conventional frames before trying to tackle a wide tire design. You must have a good bender for these frames and you must be very familiar with the characteristics and idiosyncrasies of your particular bending equipment before you tackle one of these monsters.
    If he doesn't care for the handling he can always mod/redo the frame. It's only metal. If he has lathe access he could turn a custom hub for a car wheel and spend less money, but it's probably easy to find wide tire takeoff rims.
    Last edited by farmall; 11-01-2018 at 7:52 AM.

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    My indy has a 300 wheel, many fat spokes, everything chrome and comes w/tire for sale.

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