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120/90 vs 120/80 rear tire

Discussion in 'The Garage' started by arcticXS, Aug 30, 2019.

  1. arcticXS

    arcticXS XS650 Guru Top Contributor

    I am looking into what rear tire to get next, and wonder if 120/90 is actually a better choice than 120/80, as it raises gearing between 3 and 4 percent, or slightly more than 1 tooth less on the rear sprocket. Is there any disadvantage to a 120/90 vs 120/80 that I am unaware of? I already have longer shocks, so fender clearance is not an issue. Both Bridgestone BT45 and Avon AM26 tyres are available in 120/90, so that is no problem.
     
    Rasputin and Machine like this.
  2. Rasputin

    Rasputin XS650 Addict XS650.com Supporter Top Contributor

    I guess it’s a lot down to how it will look when fitted. Originally probably had a 400/18 fitted which is quite a tall tyre
    Aspect ratio would not be far away. Can’t see a problem.
     
  3. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    gggGary likes this.
  4. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    I prefer lower ratio tires ie 80 or even 70 and adjust gearing with sprockets. What works for good handling has changed more than little since 1980 "balloon" tires. I'll assume an 18" rim here and unless you have gone much wider on the rim a 120 is too wide. But not everyone rides like a lunatic (me) on the street.
    This guide might help with reasonable choices.
    Motorcycle-Rim-WidthTire-Size-Chart-by-MTSAC.edu-2.jpg
     
    Paul Sutton and MaxPete like this.
  5. arcticXS

    arcticXS XS650 Guru Top Contributor

    I am going to fit the new tire to my new rear wheel, with a 2.50x18 unflanged Morad (Akront) alloy rim, so rim width is no issue. I went for unflanged because they are much easier to keep clean....
     
    Last edited: Aug 31, 2019
  6. arcticXS

    arcticXS XS650 Guru Top Contributor

    Well, I just ordered an Avon AM26 Roadrider in 120/90-18. I somewhat disagree with gggGary regarding changing sprockets for gearing. I currently have a 33T rear, and get pretty severe chain rub on the swing arm already, since my shocks are 343 mm/ 13,5" long. Altering gearing by tyre selection is almost free, as you need to replace them pretty often anyway. Ivan Hoey's high primary would be the ultimate solution, but I have no budget for that now....
     
    gggGary likes this.

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