I was looking to fit some gravel tires on some spare wheels for S's bike (I have 4 or five sets of spare road wheels). Unfortunately, I don't have any with an 8-speed cassette (Shimano), which is what's on her bike.
She took gravel the tires with her bike so that they can be swapped in, if she really wants to.
The smooth tires currently on her bike are 32 mm wide. The WTB gravel tires are 37 mm. Tire clearance looked OK to go up to 37...