Backspacing to Offset Conversion?

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Feb 26, 2006 | 05:41 PM

slayer6x6

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From: Drexel Hill, Pa

Backspacing to Offset Conversion?

Lets say were looking at a 19x10 wheel with 6.25" backspacing. How do I determine the offset? Will this fit a 4th gen?

Feb 26, 2006 | 06:20 PM

thesoundandthefury

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Quote:

Originally Posted by slayer6x6

Lets say were looking at a 19x10 wheel with 6.25" backspacing. How do I determine the offset? Will this fit a 4th gen?

Take the total width of the wheel and divide it by 2. Then what you get from that equation, you convert to millimeters, so:

1 inch=25.4mm
10/2=5
5X25.4=127mm

THEN

You take the backspacing measurement and convert THAT into millimeters, and subtract half the wheel width from it, so:

6.25X25.4=158.75mm
158.75mm-127mm=31.75mm

Rounding the .75 up, you're left with a 32mm offset. It'll fit, but it'll be right there on the ragged edge between being out to far and being "just right." See if you can find some pics of a car with 17X11 ZR1's with a 38mm offset. That'll be pretty close to how it'll look.

Feb 26, 2006 | 06:34 PM

slayer6x6

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From: Drexel Hill, Pa

Awesome, thank you.

Feb 28, 2006 | 09:58 AM

Chris@DTD

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thesound,

You forgot to add the 1/2" per side for the rim flange. The wheel is physically 11 inches wide.

158.75-139.7 = 19.05mm offset

Feb 28, 2006 | 11:04 AM

thesoundandthefury

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Quote:

Originally Posted by Chris@DTD

thesound,

You forgot to add the 1/2" per side for the rim flange. The wheel is physically 11 inches wide.

158.75-139.7 = 19.05mm offset

Wrong. Advertised widths are advertised widths. Not all rims have a "flange." All that is is a design style. Regardless of whether a company chooses to incorporate a flange in their wheel design, what they advertise the width as is the TOTAL width.

Feb 28, 2006 | 11:07 AM

Xsta Z 28

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Quote:

Originally Posted by thesoundandthefury

Sorry sir . . . YOU are incorrect . . . "Advertised" width of a wheel is the distance BETWEEN the bead flanges . . . always has been and always will be.

Now the "flange" is a varying dimension, 1/2" is a safe amount.

So . . A 9" wide wheel could have an "actual width" from lip face to lip face about 10" wide . .

Therefore, backspacing and offset are related, but "technically" it is not an exact science of figuring one from another, but you can get close. The one factor one MUST know to translate between them is the exact dimension of the bead flange.

Last edited by Xsta Z 28; Feb 28, 2006 at 11:16 AM.

Feb 28, 2006 | 11:30 AM

thesoundandthefury

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Quote:

Originally Posted by Xsta Z 28

Okay I'll buy the "bead flange" explanation, but the part I'm not buying is the 1/2 inch on each side bit. I just went and measured the bead flanges on the HPR5's I have and one side measures 1/4 and the other side measures 2 inches. With this much variation on just THIS wheel, I don't even wanna contemplate how hard it would be to choose a set of wheels that would fit any specific vehicle if this was the standard by which the wheel width was measured. There could be a million and one combinations for bead flange widths depending on how the wheel was designed. IMHO, measuring TOTAL width is still "safer."

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Feb 28, 2006 | 11:53 AM

Xsta Z 28

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Quote:

Originally Posted by thesoundandthefury

Okay I'll buy the "bead flange" explanation, but the part I'm not buying is the 1/2 inch on each side bit.

1/2" is not a set number, is is just a safe number that will be within virtuall every wheel makers tollerances. Also this dimension cannot be measured unless the tire is dismounted . . .

Quote:

I just went and measured the bead flanges on the HPR5's I have and one side measures 1/4 and the other side measures 2 inches. With this much variation on just THIS wheel,

Not sure how you can have a "flange" of 2". The "flange" is the small "flap" on either side of the wheel that the tire bead is pressed against. But a wheel can have a thicker flange on the inside and outside. Take for example a FIKSE 3 peice wheel, where the outside "hoop" is a rolled piece of aluminum, where the inside hoop is cast aluminum so the flange widths/thicknesses do vary.

Quote:

I don't even wanna contemplate how hard it would be to choose a set of wheels that would fit any specific vehicle if this was the standard by which the wheel width was measured.

Whether you like it or not that IS how rims are measured, advertised width is the space "between" the flanges.

Quote:

There could be a million and one combinations for bead flange widths depending on how the wheel was designed.

BINGO!!!! That is why backspace and offset cannot be directly related.

Quote:

IMHO, measuring TOTAL width is still "safer."

Not really becuase then how would a tire manufacture be able to determine if their tires fit the wheel? The advertised wheel width MUST be the tire mounting area width.

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Feb 28, 2006 | 12:29 PM

thesoundandthefury

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Quote:

Originally Posted by Xsta Z 28

Ahhh okay this is where I think the discrepancy is. By "flange," I thought Chris was referring to the horizontal "step" that extends just past the flange, (that you're referring to). THAT'S the part I was going by. Okay, so the real flange is the vertical part of the lip. This is the first time I've ever heard of wheel widths being measured by the distance between those two points. Apparently I was misinformed myself about this.

(Officially taking foot out of mouth.) My apologies to Chris@DTD and Slayer6X6 for my errors in judgment. And thanks Xsta for the new knowledge.

Feb 28, 2006 | 01:09 PM

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Xsta Z 28

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Quote:

Originally Posted by thesoundandthefury

. . . . And thanks Xsta for the new knowledge.

Hey we are all here to learn from each other. Always glad to help. Way too many terms and parts to a wheel!

Feb 28, 2006 | 05:38 PM

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slayer6x6

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From: Drexel Hill, Pa

http://cgi.ebay.com/ebaymotors/ws/eB...Pr3_PcY_BID_IT

Well this is why I was asking. Somebodys gonna get a good deal on these, I dont think Im gonna bid though.

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