Comment by fragmede

I don't know about your city, but my city, while covered in smooth surfaces, still has a lot of interactions between those surfaces. Most of the roads have a curb between the sidewalk and the road, though the ADA means there's curb cuts and ramps. I don't know that I'd agree that they're "perfectly okay". Traversing over a 20 cm/8 inch obstacle constantly seems to make wheels less than perfect.