Avon Tire Diameter

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

 

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.

 

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.

 

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.

 

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.

 

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.