A protective rim is an extra layer of reinforced rubber at the point of contact between the tyre and the rim. It is used on low-profile tyres to protect against accidental damage. Higher-profile tyres do not need a rim flange, as the rubber at the widest point forms a natural shield. Not all sizes, even within the same model, will have a protective rim. Look out for protective rim designations such as MFS, RPB, FSL, FP or FR.