Measuring Offset

[Matty K]

Hey guys; I recently changed tire size on my Mille Miglia Spiders (17"x7"), and I'm having some rub issues. Anyhow, in sorting the whole thing out, I'm trying to figure out the offset of these wheels (they were on the car when I bought it). I can't find anything online, so, is there a way to measure the physical wheel and figure it out? I have a fifth, so it's no big deal. Thanks!

 

[kw8z3boi]

HAHA. Same probablem here bro. Just got some ICW 18x7.5. Rub so much when I'm on high speed or have people sit in the back.

 

[Matty K]

Calculating offset (via Wiki):

Calculating the offset of a wheel is a fairly easy mathematical equation. First, measure the overall width of the wheel (remember, just because a wheel is 18x7.5, does not mean that the OVERALL width is 7.5”. It means that the measurement from outboard flange to the inboard flange is 7.5”). Next, divide that width of the wheel by two; this will give you the centerline of the wheel.

Overall width/2 = Centerline

After determining the centerline, measure from the mounting pad to the edge of the inboard flange (if the wheel were laying flat on the ground – face up – your measurement would be from the ground to the mounting pad). This is your back spacing.

Back Spacing - Centerline = Offset in Inches

Inches x 25.4 = Offset in mm

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I'll do this once I get back and unmount the tire on my 5th rim.