This arch kit sticks out approximately 2.75" when bodylines (wheel arch and moulding lip) are kept original. Arch is retained by screws through the moulding lip, no screws visible, and is 1" wider than the plastic type fitted by Rover but similar in shape. Fiberglass arch extends beyond the bumper seam line.
The quality of the arches is commensurate with the price. Most arches have minor flaws and require trimming for a perfect fit. The more expensive arches are obviously better quality and fit.
By fitting one of two types of sealing rubber available between the body and the arches, it makes fitment easier and a better finish quality is obtained, unless they are being moulded to the wing. 37H9871 (black, sold by the inch) is for edging trim that has only the edge butting against the bodywork.
Arch widths are measured off a new car and is the distance from the front wing (not the seam) to a point above the center of the front wheel, which is also the top center of the wheel and arch opening.
Rear wheels usually appear to stick out further than the front owing to the general bodyshape, so allow an extra 1/4" with most arches.
Widths when fitted are also dependent on the height arches are fitted and manufacturers trimmed sizes but should only vary 1/8-1/4" when fitted at the lowest position. Allow 1/8" for a rubber seal.
**Never drill the bodywork until you are satisfied with the style, fittability, and trimming requirements for a good fit!**