Finding the sweet spot between rim and tyre
Not every tyre width works harmoniously with every rim. To put it simply, the wider the tyre, the wider the rim should be. However, there are limits. If you mount a 2.1 inch tyre (54 millimetres), which is narrow in the MTB world but bulky on a gravel bike, on a 35 millimetre-wide enduro rim, you get a very "angular" tyre shape. However, because gravel tyres usually do not have pronounced shoulder lugs, this results in a narrow border area and a hard transition from tread to shoulder when cornering. In a worst-case scenario, the tyre will abruptly slip off. Conversely, the same 2.1-incher gets very little support from the rim flange on a narrow 17-millimetre road wheel rim. At low pressures and high forces, it can pull it cleanly off the rim in extreme cases, which among mountain bikers is referred to as "burping."
Below you’ll find rim-tyre combinations as recommended by ETRTO. In general, there is a trend towards wider rims, as these offer advantages in terms of tubeless riding and aerodynamics. However, approvals from rim and tyre manufacturers must always be taken into account when using them.