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XR100 spec class tire question

Discussion in 'Mini Racing' started by hrc_nick_11, Feb 14, 2015.

  1. hrc_nick_11

    hrc_nick_11 Well-Known Member

    So the tires BT45 100/90 are normally front tires so does the rear get mounted correctly or backward from the arrow?
     
  2. Kurlon

    Kurlon Well-Known Member

    Mount it backwards, at least that's what I do. :D
     
  3. noles19

    noles19 Well-Known Member

    Get the 110/90s and I flip mine and never noticed any difference in grip...
     
  4. rk97

    rk97 Well-Known Member

    the reason the tread on some fronts is "backward" is because the tire manufacturers believe it improves braking traction in the wet. Reversed forces of a rear tire somehow rationalizes reversing the tread pattern, even though the direction of travel is the same. I don't know that I completely agree with their theory, but I trust that they've done the research on something that could very easily be a liability suit for them on street tires.

    All that out on the table, I don't think the BT45 has "backward" tread on the front, so I wouldn't see the need to flip it around for rear use.
     
  5. Kurlon

    Kurlon Well-Known Member

    It's not a tread issue, it's tire construction underneath. The belting is setup to expect the primary loading in one direction.
     
  6. rk97

    rk97 Well-Known Member

    how much directional load is 6hp and drum brakes going to put on the tire?

    I've opened up seams on a flipped Dunlop Qualifier rear on a 600, but I just don't think that would be an issue with a mini.
     
  7. backcountryme

    backcountryme Word to your mother.

    Considering the tire is made for a 400 pound cruiser bike, I think that any damn way you want to run them on an xr would be just fine.
     
  8. Kurlon

    Kurlon Well-Known Member

    And when on that 400lb bike what pressure are you running at? :D

    We're running them under to WAY under inflated, and typically flexing the carcass more than they'd ever see in standard intended use. Yeah, less HP and less weight, but we're still working the tire harder.
     
  9. TurboBlew

    TurboBlew Registers Abusers

    lol... I wonder if the tire engineers @ Bridgestone ever considered the potential for them as a "race" duty tire. :D
    Its absolutely hilarious with the shenanigans you can get away with on the tire edge with the BTs. Even with the sipes gone... the tire still hooks very well in dry conditions.
     
  10. rk97

    rk97 Well-Known Member

    I used BT45's at my first 5 trackdays. they were mounted to my '97 EX500, and they impressed the hell out of me then. I was hardly even at a warmup lap pace, but my (rose-colored) recollection of them was that they performed well beyond my expectations.

    I think I was running just under 30psi. I admit that running as low as half that on the minis provides a lot more flex, but we're also talking about speeds below 55mph...
     
  11. backcountryme

    backcountryme Word to your mother.

    I don't like to run mine under 20psi. They just feel really squirmy to me. But then again I am a good chunk over 200 pounds.
     
  12. hrc_nick_11

    hrc_nick_11 Well-Known Member

    I just put them both forward, not in the mood for all the "hey do you know your tire is backward" if it does not really matter.
     
  13. Kurlon

    Kurlon Well-Known Member

    Who's going to be the first to pester him with "Did you know you're supposed to mount that backwards when running a front in back?" :D
     
  14. SICzx

    SICzx Well-Known Member

    Just finished setting up an XR100 for street track use... slapped on a set of BT45's and have a question regarding tire pressure.

    **200lb rider
    Front: BT45H 100
    Rear: BT45V 110

    What pressures should I be running?
     
  15. james walker

    james walker beat down, broken & busted

    I ran Barber last weekend with those very same tires on my XR. I weigh in around 170lbs (without gear). I ran 18lbs front and rear and they felt OK, actually thought about running a lb. or 2 higher but left it alone. Anything less than that felt 'squirmy' to me as mentioned previously by backcountryme.

    Hope that helps with a starting point.
     
  16. TurboBlew

    TurboBlew Registers Abusers

    On kart sized tracks ~15psi. That 100 front isnt really as good as the 110 when the pace picks up. Id switch the 100 to the rear and wear it out so you can get a 110 on. :D
     
  17. hrc_nick_11

    hrc_nick_11 Well-Known Member

    I'm 210lbs and I run 20-22 my sidewalks were folding on the rear with 18. On the street you can run more.
     
  18. rk97

    rk97 Well-Known Member

    Do what feels right I guess, but I much prefer 16-17 lbs. over the 19-20 i was running last year. I'm 170, but guys in the 200 lbs range run the same pressure and beat me.
     
  19. hrc_nick_11

    hrc_nick_11 Well-Known Member

    They say the 110 is stiffer and can run lower pressures.
     
  20. sharky nrk

    sharky nrk Rubber Side Up

    I always get nervous running pressure as low as you have to on these things. I had to go down to like 15lbs cold on the Sport Demons to get them to stop sliding every corner.

    The BTs I run at 17 cold.
     

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