Offset/Bolt Pattern For Dummies
08-14-2007, 07:54 PM
#1
Offset/Bolt Pattern For Dummies
Ok, I'm confused...I've tried reading, but I need a stupid person's explanation of offset. I think I've got bolt pattern down. I'm thinking that the only wheels that will fit are 5-112 for the A8L.
Offset is where I'm getting confused. How do you know the proper offset when comparing b/w 18, 19, and 20 inch wheels. Would it be the same or is there an easy way to remember? Also, how do you know if you need spacers.
Thanks in advance!
Chirag
Offset is where I'm getting confused. How do you know the proper offset when comparing b/w 18, 19, and 20 inch wheels. Would it be the same or is there an easy way to remember? Also, how do you know if you need spacers.
Thanks in advance!
Chirag
08-14-2007, 09:51 PM
#2
AudiWorld Super User
Some answers...with some background
Bolt pattern: All A4/S4/A6/S6/A8/S8 models are 5 x 112. The only modern Audi's with the 5 x 100 patterns are the transverse motor types like the TT. Q7's are different too.
Offset varies both in absolute terms, but also relative to rim width. The measurement is how far the wheel bolt up point to the hub face is from the centerline of the wheel. For a given width, the lower the offset, the more the wheel will be pushed outward toward the fender.
For the Audi A8 18's and 19's at 8 1/2 width, the offset is 45mm. The offset on the 9 by 20 is 46, i.e. essentially the same. But if you think about the math, since essentially the relationship between the centerline of the wheel and the bolt up point didn't change, that means half the width increase went toward the inside (1/4 inch), and half went to the outside (the other 1/4 inch). In the case of the A8, they can handle the increase both inward without hitting suspension parts and outward without rubbing the fenders.
If you want to give the car a more pumped up look, you can either reduce the offset somewhat in a given width, or use spacers. This will put the load further out from the bearing though and increase wear on suspension parts.
In Audi OEM rims if you are trying to achieve this look without spacers, there is little choice actually since most all the above mentioned cars were built with pretty similar offsets in a given width. The only notable exceptions are the C5 A6 4.2/C5 S6 and RS6, all of which had the big fender flares compared to the original C5. In a given width, Audi reduced the offset about 10mm. In the allroad it was even a bit more. However, if you want 18's the only real choice there would be the RS6 wheels, which are rare. I have a set, and can confirm they move the outside edge of the tire out slightly compared to the 20's on my car, even though the 20's have 275/35's and the RS 6 wheel would only use a 255/45. In aftermarket you have more choices, often around ET 35ish similar to the C5 fender flare group.
Finally, spacers allow you to do the same thing without wheel changeouts and expense. For example, see the Audiworld cover write up on SMA8L's car a few weeks ago using spacers in the rear, where the wheels are more tucked inside the fenders than the front. Same issues with more suspension loading, plus the wheel bolts need to be carefully fit and you want a high quality set where the diameter is the same as the wheel bolt up point to minimize the add on appearance.
Offset varies both in absolute terms, but also relative to rim width. The measurement is how far the wheel bolt up point to the hub face is from the centerline of the wheel. For a given width, the lower the offset, the more the wheel will be pushed outward toward the fender.
For the Audi A8 18's and 19's at 8 1/2 width, the offset is 45mm. The offset on the 9 by 20 is 46, i.e. essentially the same. But if you think about the math, since essentially the relationship between the centerline of the wheel and the bolt up point didn't change, that means half the width increase went toward the inside (1/4 inch), and half went to the outside (the other 1/4 inch). In the case of the A8, they can handle the increase both inward without hitting suspension parts and outward without rubbing the fenders.
If you want to give the car a more pumped up look, you can either reduce the offset somewhat in a given width, or use spacers. This will put the load further out from the bearing though and increase wear on suspension parts.
In Audi OEM rims if you are trying to achieve this look without spacers, there is little choice actually since most all the above mentioned cars were built with pretty similar offsets in a given width. The only notable exceptions are the C5 A6 4.2/C5 S6 and RS6, all of which had the big fender flares compared to the original C5. In a given width, Audi reduced the offset about 10mm. In the allroad it was even a bit more. However, if you want 18's the only real choice there would be the RS6 wheels, which are rare. I have a set, and can confirm they move the outside edge of the tire out slightly compared to the 20's on my car, even though the 20's have 275/35's and the RS 6 wheel would only use a 255/45. In aftermarket you have more choices, often around ET 35ish similar to the C5 fender flare group.
Finally, spacers allow you to do the same thing without wheel changeouts and expense. For example, see the Audiworld cover write up on SMA8L's car a few weeks ago using spacers in the rear, where the wheels are more tucked inside the fenders than the front. Same issues with more suspension loading, plus the wheel bolts need to be carefully fit and you want a high quality set where the diameter is the same as the wheel bolt up point to minimize the add on appearance.
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Rowingmurphy (12-17-2019)
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Rowingmurphy (12-17-2019)
08-15-2007, 06:05 PM
#5
AudiWorld Super User
Somewhat simpler version...with some real world guidance
Offset is also related to rim width in terms of how the wheel sits relative to the fender, so you need to contend with that.
Start with the basics that most stock D3 A8 wheels tend to be in the (8 to) 8 1/2 width range and their offset is around 45mm. If you want to move the wheel out toward the fenders, you need to DECREASE the offset. Aftermarket wheels are commonly available in the 30-35 mm range that would get you there. RS6 wheels (ignoring the allroad) are the only Audi OEM wheels I know of that get you to a similar result.
If you increase the rim width and you want to get to the same appearance of where the wheel is relative to the fender, you decrease the offset. Okay, here's the more complicated math: offset decreases by by half the width increase. Using a practical example, if you went from 8 1/2 to 9's, and you would have gone to 30mm on the offset in the 8 1/2 width, you would back the offset change off to more like 35mm to avoid pushing the 9" wheel too far out. This assumes there is no inside clearance problem, and on the D3 I don't see one.
Spacers are typically not something you would use together with a wheel change unless a. the wheels are super cool looking/one of a kind, or b. you have a brake caliper clearance problem. Instead, try to get the offset right in the first place and confirm the calipers clear. The other use of spacers is if you don't want to spend the $$ on new tires and wheels. Cutting to the bottom line, you might look at 15-20mm in the rear and less in the front using stock A8 wheels.
Note I don't think any of the numbers I suggested here are way radical or likely to get to where you have rubbing problems and the like--push it up to 9 1/2s, offsets down to 20 or >20mm spacers and it may get hairy.
Start with the basics that most stock D3 A8 wheels tend to be in the (8 to) 8 1/2 width range and their offset is around 45mm. If you want to move the wheel out toward the fenders, you need to DECREASE the offset. Aftermarket wheels are commonly available in the 30-35 mm range that would get you there. RS6 wheels (ignoring the allroad) are the only Audi OEM wheels I know of that get you to a similar result.
If you increase the rim width and you want to get to the same appearance of where the wheel is relative to the fender, you decrease the offset. Okay, here's the more complicated math: offset decreases by by half the width increase. Using a practical example, if you went from 8 1/2 to 9's, and you would have gone to 30mm on the offset in the 8 1/2 width, you would back the offset change off to more like 35mm to avoid pushing the 9" wheel too far out. This assumes there is no inside clearance problem, and on the D3 I don't see one.
Spacers are typically not something you would use together with a wheel change unless a. the wheels are super cool looking/one of a kind, or b. you have a brake caliper clearance problem. Instead, try to get the offset right in the first place and confirm the calipers clear. The other use of spacers is if you don't want to spend the $$ on new tires and wheels. Cutting to the bottom line, you might look at 15-20mm in the rear and less in the front using stock A8 wheels.
Note I don't think any of the numbers I suggested here are way radical or likely to get to where you have rubbing problems and the like--push it up to 9 1/2s, offsets down to 20 or >20mm spacers and it may get hairy.
08-16-2007, 11:17 AM
#7
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Re: Somewhat simpler version...with some real world guidance
I have 9" wide wheels with 35mm offset (245/30/22 - tires flush with outer rim) and 15mm spacers in the rear. This is the absolute limit of pushing the wheel outward, one more millimeter would be too much.
From a factoy 17 X 8.5 rim you add the following:
Offest +10 mm (from 45mm to 35mm)
Rim width + 1/4" (6.25 mm) (from 8.5 to 9 - divide by 2)
Spacers 15 mm
REAR
So on the rear, technically you can go a maximum of about 32.25 mm (1.29")more outward from a factory 17" wheel without any rubbing. This max width really only applies when the car is lowered. No rubbing at all should occur even if you go wider than the "technical maximum" with the stock ride height because you wheel will never travel that far up under your wheel well
under normal driving conditions.
Max on the rear is 10" with no less 30mm offset.
FRONT
Max I would recommend is 9.5" and no less than 30mm offset.
From a factoy 17 X 8.5 rim you add the following:
Offest +10 mm (from 45mm to 35mm)
Rim width + 1/4" (6.25 mm) (from 8.5 to 9 - divide by 2)
Spacers 15 mm
REAR
So on the rear, technically you can go a maximum of about 32.25 mm (1.29")more outward from a factory 17" wheel without any rubbing. This max width really only applies when the car is lowered. No rubbing at all should occur even if you go wider than the "technical maximum" with the stock ride height because you wheel will never travel that far up under your wheel well
under normal driving conditions.
Max on the rear is 10" with no less 30mm offset.
FRONT
Max I would recommend is 9.5" and no less than 30mm offset.
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11-01-2018, 07:25 AM
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Offset 2008 A6 3.2
What is my offset for my 2008 A6 3.2. I came across somewhere that it said 43 mm. What to make sure it is correct. Looking to buy some new rims which are 19x8.5 bolt pattern 5x112. Offset is 35mm