I did mod a little these are arched , there not the same width all the way through there fat in the center then get narrow on each end and they have a lip inside . They go outward away from the wheel so I trimmed the lip under Neath or back side with a flap disk to be sure they don't rub my tires I'm around 4" or so lower with bc 5k springs in rear my tires were just slightly stretched there taller than the stock kumho that were on it .
Attached using rivet nuts bought the tool from harbor freight it came with 10 I needed 12 for the rest 12 for the front I bought x tra nutserts elsewhere so I can take them off repaint replace etc , I did need to fold the outer edge of my rear fender lip , it was easy using a pipe , bat , and a snap on catalog ......raised car then lowered it onto the pipe rolled it hitting the pipe with a rubber mallet .
Depending on how low you are you might not need to but I didn't care my tires hit if I didn't 9.75" wide wheels now they never hit ..fwy bumps no problem .