I have a 2003 F150 FX4, and I am going to buy a set of Xd Series Rockstars. I want the same backspacing as my stock wheels. The only problem with that is I have no clue what that backspacing is! If anyone can help me out with this, I would greatly appreciate it. Thanks

 

My '03 Screw FX4 had 14 mm offset rims. That's the factory FX4 rims.

 

Alright every site i went to where i could buy the wheels does not have 14mm as an option. the closest it has is 12mm. And it also asks for backspacing and I have no idea what that is.

 

You can calculate backspacing if you know the offset. There's a calculator or thread here somewhere that explains how. I bought these: http://cgi.ebay.com/ws/eBayISAPI.dll...m=370784966158. They have an 18 offset. I put 285/70 Nitto Terra-Grapplers on them and they fit no problem. I haven't lifted my truck, but I did crank up the t-bars. I decided I wanted them to be spaced out more, and tried 1" spacers behind them, which turned them into -7.4MM offset wheels. The tires rubbed a little on the front fender valance when I'm in reverse and turn the wheel to the right. They clear if I turn it the other way. I cut 1/4 inch off the valance and the tires cleared after that.

Basically, positive offset means the wheel is spaced inwards from being centered (with half the wheel being to the inside of the flat mounting surface on the rotor, and half being to the outside). Positive offset moves the rim inward, and negative offset moves the rim outward (widens the stance! ).

Also, the tire calculator on the site here will tell you how much difference you will get with different offsets. Put in your current rim and tire dimensions (14mm offset), enter your new sizes, and it will tell you how much difference there will be inside, outside and diameter wise from the new setup and the old setup. With the 18 offset and larger tires, it said I would lose about 2/3 of an inch of clearance inside. That still cleared the suspension and fenders. Oh yeah, 1 inch = 25.4MM for conversion purposes.

Hope that helps. Let me know.