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Tire Size using slightly larger diameter ie 12/90 vs 110/90

Discussion in 'XJ Technical Chat' started by seca550RK, May 29, 2017.

  1. seca550RK

    seca550RK Member

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    Hey everyone, I'm looking for some opinions on tire size.

    I am in the north of Norway and the only readily available tire for my '84 xj600 is a 120/90/18.
    Stock size is listed as 110/90/18

    If I understand the aspect ration 120 x .9 = 108mm and 110 x .9 = 99mm

    Will this 1 cm larger diameter fit first of all, and do you see it having any negative affects on handling?
    I'm not worried about the different gear ratio as the bike has plenty of power

    Let me know what you all think!
    Mike
     
  2. seca550RK

    seca550RK Member

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    sorry total of 1.8cm larger diameter, effectively double what I posted
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    it is more about how wide the tire is and if it will fit
     
  4. Wintersdark

    Wintersdark Well-Known Member

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    The OD should be fine, but I know on my Maxim there's VERY little room between the drive shaft and tire width wise (and be sure to check for enough room by the swing arm at the front if the tire is a bit larger in diameter as well). I'm not really clear on how tire measurements work, but that'd be pretty easy to measure if you've got the current tire on your bike still.

    There should be much more than 1cm in clearance for the swingarm before maxing out, but you could test that too. Just put something, say, 2cm high on top of the tire that'll mark the fender or deform in some way, then compress the back end till it maxes out. Then you'll see if you've got room.

    I've never changed rear tire sizes, but I can't imagine a very slightly larger in diameter tire having an appreciable affect on handling, though it will change (as you noted) resulting rpm:speed ratio - you'll go faster at a given RPM, but have slightly less power.

    You are talking about the rear, right?
     
  5. k-moe

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

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    A wider tire will slow handling, but is safe to run.
     
  6. KrS14

    KrS14 Active Member

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    Remember, if your speedo is run from your front wheel, the size change will throw the speedo off.
     
  7. seca550RK

    seca550RK Member

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    Thanks for the replies
    I'm actually waiting for the bike to arrive, since I'm importing from Sweden. It would be pretty simple to
    See if i had it here.
    I think it should be a small enough difference that it won't touch anywhere.
    As far as the width, it had a 120 mounted before so I'm not worried. I plan to do some 2 up touring so the larger tire should help it feel more stable with the weight, and maybe last a little longer.
    I found a bridgestone bt45 that should suit my needs.
     
  8. a100man

    a100man Well-Known Member

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    I fitted this one.. Maxxis M-6103 Promaxx 110/90-18 61H from Tyreleader good price and I think they ship all around Europe. J
     
  9. Kickaha

    Kickaha Active Member Premium Member

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    We always fitted the 120/90-18 on the XJ550, more tyre choice and the size difference wasn't really noticeable, the BT45 is really good, I used to race my RD350LC on them
     
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  10. Bleechmint

    Bleechmint New Member

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    I've been curious about this subject as well. I was thinking about doing something similar to this but obviously I would need to put a bigger front tire on my 83 XJ750K. The questions I guess would be what are the minimum clearances needed for the tire widths. How much do the tires expand once they're hot and at speed? I think the rear tire has much less room to expand with the swing arm dimensions but I think there is much more room for height as well as width between the forks.
     

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