Brendan,

The 18" wheels will actually not fit because of the larger spindle size used for the kit. The 18" wheels will not clear these spindles, 20" wheels are the smallest you can use with this specific kit.

Let me know if you have any other questions.

Matt

I just ordered a 2009 FX4 and it is should be here in 6 to 8 weeks. I plan on lifting the truck shortly after I get it, and I would like to get the Pro Comp lift for it, but I am concerned about the wheel situation. I ordered it with the 18" wheels, which I will still want to use during the winter. The description says that it will accept 37's on 20" or larger wheels. Does that mean that I would be required to run 20's all the time with the Pro Comp lift? Thanks for the help.

-Brendan