When Woody did the rear on my 8GS I didn't know I had the option for an 18. Dang. Slightly off topic, but he wouldn't make the front 21 tubeless. Don't know why. Anyway, I'll have a new to me '10 KTM 690ER and it comes with the 18/21 combo.
'14 R1200GSW; '14 F800GSA
'10 690 EnduroR; '11 WR250R