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Discussion Track tyre sizes - FZR250 2KR

Discussion in 'Yamaha 250cc In-Line 4's' started by Russry, Jul 13, 2021.

  1. Russry

    Russry Active Member Premium Member

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    What tyre sizes and brands are people running on track bikes?
    From what I understand, you can fit a 120/70 front and 140/50 rear on stock wheels.
    I have a 87 2kr

    Cheers
     
  2. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    100/80/17 and 120/80/17 are standard sizes for 2KR. 3LN is the same front but a 130/70/17 rear.
     
    Last edited: Jul 13, 2021
  3. mboddy

    mboddy Well-Known Member Premium Member Contributing Member

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    Those sizes are for the wider 3LN wheels 2.75x17 and 3.50x17.
    You need to use narrower tyres to suit the 2.15x17 and 2.50x17 wheels on the 2KR.
    Bridgestone BT39SS are track tyres with sizes to suit your rims.
    Don't get BT39 as they are street tyres. BT39SS are Super Sport race tyres.
    In Australia Whites Racing Products are probably your only source.
    90/80 front and 120/80 rear
    https://www.bridgestone.com/products/motorcycle_tires/products/battlax/bt39ss.html
     
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  4. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Didn't have time to post properly before, but going for wider tyres is often not productive on the smaller bikes - slows down handling and direction changes especially from full lean one way to the other. The advantage of these small bikes is that they are very nimble and can run rings around bigger bikes where it matters, with a skilled rider.

    You also don't have as much power to play with, so you are using what you have nearly all the time, while the bigger bikes are still braking and setting up their 'point and shoot' style, you will be on the power the whole way through.

    My anecdotes on riding 3LN FZR250's - the 100/80/17 and 130/70/17 setup was noticably more nimble than a 110/70/17 and 140/70/17 configuration. I haven't ridden a 2KR so I can't really comment on what they're like, but I would imagine they are slightly more nimble given the smaller tyre and rims.
     
  5. gregt

    gregt Well-Known Member Premium Member

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    The rim sizes for RS125's and Moto 3 bikes are 2.5in front and 3.5in rear. Slicks for those can be fitted to the 3LN rims.
    Forget nimble - that can be adjusted in. Grip is paramount.
     
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  6. mboddy

    mboddy Well-Known Member Premium Member Contributing Member

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    Moto 3 slicks are the best tyres if you fit a 3LN rear wheel (it goes straight in).
    Note that you cannot use them in Australian Historic Road Racing P6 Production class.
    The specs for the Bridgestone front slick say it is ok to use with the 2KR 2.15 front wheel.
    If you really get carried away you can also fit either the TZ125 or SRX400 2.5x17 rim to the front.
    If so I would recommend the SRX400 rim over the TZ125 rim because it will handle off track excursions much better.

    When I compared the slicks in 90 and 120 sizes against the 100/80 17 and 130/80 17 tyres the wider tyres made the bike feel very slow steering.
     
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  7. Russry

    Russry Active Member Premium Member

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    Can't use the slicks or the rear wheel?
     
  8. Russry

    Russry Active Member Premium Member

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    Thanks, this gives me a good starting point and I can just play around with it a bit more.
    Would it matter much with me being a bigger dude? I'm 105kg and 6'1, obvs I'm not going to be as fast as someone who weighs less but I'm just curious if the tyre size would make a difference due to my weight
     
  9. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Yes definitely, these bikes are designed for small japanese jockeys. You will need suspension tuning, most likely springs in the forks. Not much adjustment available on these other than preload on the rear, and changing springs in the forks. Someone might do some gold valve emulators
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    There are some suspension guides in the resources section. RaceTech can do gold valves for just about anything if you can give them dimensions. Normally I shy away from recommending larger tyres, but for a big fella like yourself I would say definitely go up from standard.
     
  11. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  12. Russry

    Russry Active Member Premium Member

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  13. Russry

    Russry Active Member Premium Member

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    I'll look into the forks as I know they can't be modified to compete in period 6 but can you swap out the rear shock? I had a read through but wasn't sure
     
  14. mboddy

    mboddy Well-Known Member Premium Member Contributing Member

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    You should fit the emulators and springs to improve the underdamped undersprung JDM forks.
    You can change the shock for P6.
     
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