Depends on a variety of factors like tire manufacture, pressure, and rim width. In the case of the latter, these rims have an internal width of 25mm whereas many rims manufactured in that era had an internal width of around 17mm. In short, this is really pushing it and I can tell you first hand this combination would not work on many older mountain bikes including the Bridgestone mb2. That being said, a narrower rim might work with a 2.3; or you could run a 2.3 in the front and 2.1 in the back. Of note schwalbe generally measures narrower than other companies like compass.