A rim for a mountain bike is provided, including a rim body having a rim well, a rim base and two lateral rim flanks and a hollow space device with a hollow space. A width of the rim body is larger than 30 mm. The hollow space device of the rim body is radially outwardly limited by the rim well and laterally and radially inwardly, by an inner enclosing wall including the rim base and the rim flanks. The radially inwardly enclosing wall forms an internal wall that is substantially closed, apart from the nipple accommodations. The rim well includes a plurality of recesses having a surface proportion of at least 10% of a surface of the rim well.