Originally Posted by
noglider
There's something funny with my spd sandals. They don't chew up my soft wood floors in my house. They don't grind on the ground outside when I walk on asphalt or stone, but they grind like crazy on concrete. Why is this?
My guess is that the tread around the cleat is worn down just enough that the cleat is lightly touching the surface. Wood and asphalt are slightly soft and slightly quiet, so the light contact the cleat makes with them is not doing obvious visible damage (yet) or making noise, but if you examine your floor closely, you may find very faint scratches from the cleat. On the other hand, concrete is very rigid and noisy, so the slight contact the cleat makes is creating a loud clack or scratchy noise.
I'm not sure why you haven't noticed an issue with stone. Perhaps the surface is bumpy and the cleat often falls in the gap and doesn't make contact.