Originally Posted by Lars
I know the size of the front tire of my R 100 GS as being 120/90/90 - 21"
A tire dealer in Delhi told me that would be the same than 275.21
Is that true?
The correct size is 100/100-21, but I have used both 90/90-21 and 3.00-21.
The point we are missing here are the tire ratings, for the GS, you need at least a 51R rating and you are not going to find that on a 2.75. Not to mention, you probably couldn't get it to mount tubeless because it's too skinny. Running a 2.75 on a GS is down right dangerious, so don't do it. Find the strongest 3.00-21 and run that. Even if it's not tubeless, you can run it that way. Only as a last resort, install a tube.
Playas del Coco
"..an attaching bike on which one rolls serenly along."
(Google translation of a French R100GS review)