Dear Tom and Ray: My wife, while driving her 2011 Cadillac CTS coupe, ran onto a tree limb that fell off a truck in front of her. She stopped, backed up and eventually pulled the tree limb back out from under the car. Hitting the tree limb severed the black plastic/rubber or whatever part under the front bumper. I tied up the black thing, which I think is a wind diverter, to keep it from dragging and took the car to the dealer. The dealer removed the severely damaged part. My question is: Should I have the piece replaced, or let it go as is? Aesthetically, I can't tell the difference with or without the diverter, but if the thing has a purpose, I will have it replaced. -- Tom

TOM: You can forget about it, Tom. That little rubberized flap is called a chin spoiler.

RAY: It's got about as much functional purpose as my brother's "chin spoiler" -- i.e., his beard. It catches a little soup once in a while, but it doesn't do anything to make him perform better.

TOM: The chin spoiler is a small air deflector that's supposed to make the underside of the car a tiny bit more aerodynamic, especially at high speeds. Is it something you'd ever notice in the performance of the car? Nah.

RAY: There are a couple of small side benefits of having the chin spoiler there. It may provide a little bit of scratch protection to the underside of that bumper when you run over a curb stone or a tree limb.

TOM: And it may keep some small bits of debris from getting up into the belt assembly area.

RAY: And like my brother's beard, it helps hide whatever ugly thing is underneath it.

TOM: But it probably would cost you about $200 to get a new one installed, and if it were my car, I'd forget all about it and keep driving.