Ford Focus Forum, Ford Focus ST Forum, Ford Focus RS Forum - View Single Post - All Technical Info
View Single Post
Old 10-27-2011, 04:05 PM   #4
Dr. Woo
Focus Enthusiast
 
Dr. Woo's Avatar
 
Join Date: Oct 2011
Fan#: 90817
Location: Hampton Roads, VA
What I Drive: 2012 Focus SE Sport SGM

Posts: 277
FF Reputation: 0 Dr. Woo Newbie
Buy-Sell-Trade Rating: (0)
Looking at diagrams of wheel measurements, it seems that backspacing is the distance from the inner rim of the wheel to the hub mounting point. This can be calculated by dividing the wheel's width in half (thus determining the centerline) and then adding (or subtracting) the wheel's offset.



With many of the wheels said to fit a 2012 Focus (5x108 bolt pattern, high positive offset), it seems their measurements are incorrect. For example:
Enkei Performance Ammodo
18x8
Offset: +38mm
Backspacing: 6.06"
Bolt Pattern: 5-108
Rec. Tire Size:235/40-18
Weight: 23.4lbs.
One or more of these measurements must be incorrect. An 8" wide wheel's centerline is 4", or 101.6 mm. Add the offset and you get 139.6 mm of backspacing, which is about 5.5". That's off by over half an inch.

These kinds of measurements are crucial on newer cars with ever-increasing factory offsets. Are these numbers supplied by the manufacturer?

EDIT: Did a bit more research and found that wheel width is not equal to overall wheel width, and 1" is a relatively safe amount to add to determine overall width. That means this particular wheel would have a centerline at approximately 4.5", and adding 38 mm of offset (1.496") would put you at 5.996" of backspacing. Looks to be more accurate, but to get 6.06" of backspacing this wheel's overall width would have to be 9.128".
__________________
╠╬╝ 2012 SE Sport - SGM | 2009 Pontiac G8 (2011-2011) | 2008 VW R32 (2007-2011) | 2006 VW GTI (2006-2007) | 2001 Audi A4 (2002-2006)

Last edited by Dr. Woo; 10-31-2011 at 03:57 PM.
Dr. Woo is offline  
    Reply With Quote