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Old 12-29-2009, 10:05 PM   #1
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I dont understand offsets, Will these rims fit my 01 Boxster

Hi I asked a similar question before but these are a different set of rims
FRONT: 8 1/2 X 19 ET 25 AND REAR: 11 X 19 ET 40

What does the ET 25 and Et 40 mean?

Will they fit my 01 S?

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Old 12-30-2009, 04:23 AM   #2
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Read about it here:
http://www.tirerack.com/wheels/tech/techpage.jsp?techid=101

And calculate it here:
http://www.1010tires.com/WheelOffsetCalculator.asp

I don't think those wheels will fit your Boxster though because the rear width (11in) is too wide. Max That will work, I think is 10.5, and that is pushing it.

I'm no offset expert, so others should chime in, but the original offset offered on the 17in Boxster wheels was ET 55 front, ET 50 rear, so depending on what the specs are on your new wheels, you may need spacers. Don't forget, with spacers, you'd then also probably need to buy longer wheel bolts.

I found it easier just to find a set of wheels that have an offset and width made specifically for the Boxster so that I didn't have to add spacers at all, and could just bolt them on without having to buy longer bolts either. The wheels I bought have the following specs:
Fronts 18x8 / ET49
Rears 18x9.5 / ET43

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Old 12-30-2009, 04:46 AM   #3
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There is no way that an 11 inch wheel will fit on a 986 boxster. Also, you should check the offset again on that front wheel. Its not possible that I would have a +25 et. I can't imagine that there is any Porsche vehicle that could accommodate such a low offset as that.
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Old 12-30-2009, 04:56 AM   #4
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Quote:
Originally Posted by Johnny Danger
There is no way that an 11 inch wheel will fit on a 986 boxster. Also, you should check the offset again on that front wheel. Its not possible that I would have a +25 et. I can't imagine that there is any Porsche vehicle that could accommodate such a low offset as that.
He probably meant 52.
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Old 12-30-2009, 05:14 AM   #5
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Essentially, offset refers to the distance between the centerline of the wheel and the rear hub mounting surface (sometimes referred to as the "back pad" ). Depending on the offset, this determines where the wheel will "sit" in the fender well. The higher the offset, the more the wheel will sit inward toward the strut. The lower the offset, the more the wheel will push out toward the fender lip. For the most part, Porsche enthusiasts who are interested in upgrading their wheels, typically look for ones that have a lower offset. This is what creates that more aggressive look or "stance". Upgrading one's wheels is all well and good. However, most do not realize how critical this application is. As well balanced and poised as the Boxster is, in my experience it is also a hypersensitive vehicle. Precise fitment is extremely crucial.
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Old 12-30-2009, 05:42 AM   #6
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Also, wheel diameter is irrelevant when it comes to calculating offset. Initially, its the width of the wheel that is important. For example, to compare a wheel that is 17x9 +55 and one that is 19x10 +40 as it relates to where the wheel will sit in the fender well is based on the difference of width and offset. Essentially, the 19 inch wheel will result in 2 mm's more inner clearance than the 17, and the wheel will extend out toward the fender lip an additional 28 mm.


Last edited by Johnny Danger; 01-07-2010 at 05:11 PM.
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