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Tire sizing

Discussion in 'XJ Modifications' started by rainman, Sep 14, 2015.

  1. rainman

    rainman New Member

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    Wondering if anyone knew what the largest size tire I could safely fit on the rear of 82 xj750? Need new tires and I feel the rear tire now is way to skinny for the size of the bike (looking at it from the rear).
     
    rainman, Sep 14, 2015
    #1
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The stock size is not too skinny (wide tires can actually hamper performance). The stock tire size is what fits. With careful attention to the sidewall construction you can just barely go up one size on the rear without having the tire rub on the swing arm.
     
    k-moe, Sep 14, 2015
    #2
    Jowzeerider likes this.
  3. Polock

    Polock Well-Known Member

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    What size is on it, maybe it is too small
     
    Polock, Sep 14, 2015
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  4. rainman

    rainman New Member

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    I'll take a look when I get out of class and let you know. It just seems small. Then bile from behind looks like a wide hip with baby legs.
     
    rainman, Sep 14, 2015
    #4
  5. Toomanybikes

    Toomanybikes Well-Known Member

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    Big tire on the stock rim might look cool but doesn't handle any better! Might even be worse as it will pull sidewall of tire in farther than its designed to! Stock rear in modern metric size is a 120/80-18
     
    Toomanybikes, Sep 15, 2015
    #5
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The stock rear on the 750 is (and has been since new) 120/90-18. I'm sure that he'd like his speedometer to be at least somewhat accurate.
     
    k-moe, Sep 15, 2015
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  7. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    That's how all bikes used to look before the "wider is better" movement of the early 2000's.

    A wide rear tire has a larger radius (through the cross-section), which means that the motorcycle has to rotate through a larger arc (greater distance) when rolling (think of how an airplane rolls) into or out of a turn. That action slows handling (sometimes very significantly).


    The irony is that even though a tire is wider, the contact patch of the tire does not increase as much as the increase in tire width would suggest. In the real-world of street riding all a wider tire does is make a bike look different.
     
    Last edited: Sep 15, 2015
    k-moe, Sep 15, 2015
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  8. Toomanybikes

    Toomanybikes Well-Known Member

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    I stand corrected
     
    Toomanybikes, Sep 15, 2015
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  9. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    So do I.
    I read your post and thogght nothing of it until I checked the air pressure on my rear tire and happened to look at the size. I double-checked before I posted, thinking that maybe I had been running the wrong size rear.
     
    k-moe, Sep 16, 2015
    #9
  10. Jowzeerider

    Jowzeerider New Member

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    I read somewhere that 130-90-18 is the biggest tire that wil fit the bike without clearance issues. The size is actually considered to be a "common" upgrade, according to the article. 140's do not work (rubbing against swingarm) unless modifications are made to the swingarm. Has anyone tried 130's?
     
    Jowzeerider, Apr 20, 2016
    #10
  11. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    A lot of people have tried, and do still run 130 tires. Widths vary though, and it's the sidewall transition that can cause rubbing more than the actual stated width will.
     
    k-moe, Apr 20, 2016
    #11

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