Scott windriver tire clearance
 

HI! I have a vintage scott mountain bike, windriver sports. Right now I'm using with 26x2,1 Schwalbe Billy Bonkers. Anyway, I can't find out how much wider I can go. In the front the space is plenty, but in the rear it seems really tight. Does anyone using it with 2,2 or upper sizes?

Measure the distance between the chainstay. Should give you an approximate idea.

Measure twice, cut once! Check all the points where you would have rubbing and see what you can fit but also keep in mind if you are planning on doing some mountain biking you will want some clearance for mud unless you are lucky enough to live in a place that is always dry and won't ever encounter dirt. Ideally for mud usually 4mm or more is good if not I would at least give 2mm on either side or just say hey, I can't run super wide stuff and that is OK. Then get a bike that is more practical for the tire widths you desire and keep that one for having fun on because vintage MTB can be fun.

It is impossible for us to know. You have the bike and can see how much room there is. The problem is tires rarely measure what is marked on the sidewall.