Avon Tire Diameter

Discussion in 'Tyres' started by Tom Swift, Apr 21, 2022.

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  1. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    140
    43
    USA
    #1 Tom Swift, Apr 21, 2022
    Last edited: Apr 22, 2022
    These are the Avon tires that fit the 2.75" and 4.25" rims. The last two dimensions are advertised tire width and diameter. Changing the overall diameter ratio between front and rear could affect ABS. Too big on the the front could cause the ABS to kick in early. Too little could make it kick in too late. I don't think it automatically recalibrates because I've never heard of an ABS that does. I went from a 21" rim to an 18" on one of my bikes and rear ABS kicks in almost immediately and the front never kicks in. I disabled it completely on that bike because even when stock, it interfered with my braking on dry roads and almost caused a crash, once. In the wet, it was probably good.

    FRONT
    Phantom 100/90-18 56H 100 637 *
    Roadrider 100/90-18 56H/V 108 642
    Roadrider 110/80-18 58V 111 640
    Roadrider 110/90-18 61V 116 663
    Spirit ST 100/90ZR18 56W 107 636
    Spirit ST 110/80ZR18 58W 109 633
    Storm 3D 110/80ZR18 58W 109 633
    AM22 (Race) 110/80VB18 112 625


    REAR
    Phantom 150/70R17 69H 150 642 *
    Roadrider 140/70-17 66V 140 641
    Roadrider 150/70-17 69V 156 656
    Spirit ST 150/70ZR17 69W 153 643
    Spirit ST 160/60ZR17 69W 161 649
    Spirit ST 160/70ZR17 73W 166 656
    Storm 3D 150/70ZR17 69W 153 643
    Storm 3D 160/60ZR17 69W 164 629
    Storm 3D 160/70R17RF 79V 166 656
    AM23 (Race) 160/60VB17 170 630

    Sport (no front)
    3D Ultra Evo 160/60ZR17 (69W) 162 628
    3D Ultra Evo 150/60ZR17 (66W) 157 615

    Tour (no front)
    Cobra Chrome 180/60B17 75V 175 655
    Cobra Chrome 160/70B17RF 79V 156 662
     
    • Like Like x 1
  2. joe mc donald

    Dec 26, 2014
    13,874
    1,000
    slough / burnham
    Tom Swift
    Useful bit of info. Thanks for sharing that
    Joe.
     
  3. capt

    capt Elite Member

    May 8, 2016
    3,052
    750
    western Australia
    My understanding of ABS , tyre size nor rim size would affect it !!
    The sensor Pick's up wheel rotation , not , wheel sizes ! Any wheel that is locked up isn't rotating , so abs would release the pressure until wheel is rotating again ! Size might affect sensitivity ! But wouldn't stop it working ...
     
    • Agree Agree x 1
  4. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    140
    43
    USA
    Depends on how sophisticated it is. If the system compares front and rear wheel speeds and detects one wheel turning slower than the other, it thinks it's losing traction and intervenes. The tire that's spinning faster because of a smaller than stock diameter, can lose traction without slowing enough to trigger the ABS until it's too late. The older rudimentary systems aren't linked and the more sophicated system uses lean angle sensors. I went to a smaller front wheel and ABS prevented even moderate rear braking but I couldn't get It to kick in on the front. It would be really bad to increase the front wheel size and lose the front braking during an emergency stop.
     
    • Useful Useful x 1
  5. brown mouse

    brown mouse Elite Member

    Sep 15, 2018
    2,288
    943
    East Midlands, UK
    I sincerely doubt they're that stupid. The computer controlling things can easily compare speeds between both wheels and work out what 'normal' is. Any hard coded values for these ratios will not only be wrong for different tyre brands, but also for states of tyre wear and amount of inflation.

    In fact, after I turn my Triumph on, the ABS warning light doesn't go out until I've done a few wheel turns of motion, presumably because its a) verifying sensors work and B) working out what the wheel relative sizes are.
     
    • Agree Agree x 1
  6. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    140
    43
    USA
    Your doubting doesn't change the facts that I've proved consistantly. With the 3" smaller front wheel, my ABS light went out once I got rolling, too, but it doesn't indicate that the tire rolling speeds are correct. It only knows the sensors are working. It doesn't care if the wheels aren't turning at any specific speed until the brakes are applied and then the slightest variance will put it over the threshhold of when it thinks the increased diameter wheel is turning too slowly.

    Once the ABS intervenes, the light comes on and the whole time the rear brake pedal is pulsing until I let up. It resets and I can make it do it again and again with very little pedal pressure. With the front wheel being so much smaller, I couldn't get the ABS to intervene at all without risking a crash. With the stock 21" wheel, I could easily get the ABS to pulse the brake lever. It's all very much reapeatable WITHOUT A DOUBT!

    As further proof tire diameters matter, the same bike that came stock with the smaller front wheel used a smaller ABS rotor with less windows so there's no basis for your arguments.
     
  7. PatW

    PatW Senior Member

    Apr 4, 2021
    762
    193
    Cymru
    They can generally handle differences in tyre diameter up to an inch.
     
  8. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    140
    43
    USA
    Brown mouse, if you've ever had the ABS kick in on dry pavement (not leaned at all) and cause your bike to loose 10' or so of braking distance in a fraction of a second in an emergency situation, you'd know that our ABS system isn't very sophicated. I had to steer in between stopped cars before I came to a stop. F*ck ABS on bikes! I've ridden many bikes for many years and my first ABS bike thought it was smarter than me. It works best if both brakes are being applied so they can have a more synchronized wheel speed but I rarely use the rear so after going to a smaller front rim, it didn't bother me that the rear brake was barely effective as long as the front brake wasn't affected as it was with the bigger stock wheel.

    The Triumph ABS can't be turned off for dry pavement and I'm not going to remove it so I have to ride it a bit more sedately. I can get it to pulse to lever so I know it's limitations.
     
  9. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    140
    43
    USA
    Just keep in mind that a larger diameter front (front/rear ratio) will cause that wheel's ABS to kick in sooner. Most tire combos Avon offers would effectively delay front wheel ABS intervention although, it would be barely noticeable if at all compared to my 3" front wheel reduction.
     
    • Funny Funny x 1
  10. PatW

    PatW Senior Member

    Apr 4, 2021
    762
    193
    Cymru
    I wouldn't ever buy a bike with abs
     
  11. Tom Swift

    Tom Swift Active Member

    Sep 24, 2021
    140
    43
    USA
    It's easy to disable with new brake lines. One of these days I'll remove the pump. The ABS light doesn't bother me.
     
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