| Re: C4 Technical FAQ and Summary |
Subject: Re: C4 Technical FAQ and Summary by WVZR1 on 2009/3/4 3:31:32 It appears that the "wheel offset/front spacing/rear spacing" needs some attention. The math is flawed. The correct math for front or rear "spacing" is done from "TOTAL" wheel width and not "advertised width" bead to bead. I've seen these figures posted on other forums "as fact" and never actually knew from where they came. Someone PM'd me the thread and I thought I'd check it out. The easiest way to "correctly" establish "front spacing" is to first calculate "rear spacing". Front spacing is the "simple result" of subtracting the "rear spacing" from the "TOTAL" wheel width. The math when "advertised offset" is known: (offset)/25.4 = X + (total wheel width)/2 = "back spacing" "front spacing" = (total wheel width) - (back spacing) It is generally accepted fact "total wheel width" is "advertised width" + 1"(1/2" each bead flange"! A simple example: C4 9.5/56mm 56/25.4(2.205) + 10.5/2(5.25) = 7.45 (BS) 10.5 - 7.45 = 3.05 "front spacing" The math from "advertised back spacing": (back spacing)- (total wheel width)/2 = offset The same C4 9.5/7.45: 7.45 - (10.5/2)5.25= 2.2 X 25.4 = 55.88 (offset) round up 56mm This math is using "generally accepted" allowances for 1/2" bead flanges. There are "minimal" differences wheel to wheel! I didn't do the math for all wheels but it appears that all were calculated in the same fashion so I anticipate the same eroneous information. I'm quite comfortable with my numbers and my math. |
