[Hui]

My understanding of it is that the speed sensing is taken from the general abs circuit and if the wheel size is changed then the difference is detected as a fault or it thinks a skid is imminent. There is a tollerance to allow for worn and new tyres but will not allow for a decent change to a 19" rim for example.
I've never really worked out if it was just the front or rear sensors for the speedo but thought it was mainly the front for some (no) reason.

 

[Derek]

Definitely the rear used for the speed on my Multi. When the front sensor failed the speedo worked just fine but the ABS and DTC switched themselves off. A difference in tyre sizes will results in different pulse frequencies from each wheel. If the bike has DTC, which the Scrambler doesn't, that will be switched off. I'm not sure if it would affect the ABS or not, but probably yes.

 

[Hui]

There may be a move to the front sensor for speedo in the future if Ducati/Bosch follow KTM as my 1290 Superduke and others can switch abs into Supermoto mode which turns off the rear abs to allow for drifting into corners.

 

[Ogre]

FWIW...Dunlop Roadsmart 3 touted as "improved" are available in stock sizes.

Dunlop Roadsmart 3 Review | Performance Motorcycle Touring Tires

 

[TastyTreat]

Definitely the rear used for the speed on my Multi. When the front sensor failed the speedo worked just fine but the ABS and DTC switched themselves off. A difference in tyre sizes will results in different pulse frequencies from each wheel. If the bike has DTC, which the Scrambler doesn't, that will be switched off. I'm not sure if it would affect the ABS or not, but probably yes.

I have a Sixty2 - the 400c scrambler and I'm considering putting on Continental TKC80s or Pirelli Scorpions. Is it a difference in tyre size that may affect the Speedo/DTC/ABS etc? Or a change in wheel size (as in .. going from 17" to say 18")?