Technical folks: need help figuring out proper wheel offsets

Offset is the difference between the measured distance from the inside mounting face of the rim to inner rim edge and mounting face to the outer rim edge. if the distance is the same, you have 0 offset.

offset is only going to help you with regard to the front and rear tracking of the tires. the diameter change on a 2008 audi I believe will cause more problem than maybe it is worth.

Most newer cars are designed and suspension is tuned to the tire size. systems such as anti-lock brakes, traction control, suspension dampening will most likely be affected by this change.

I would suggest contacting Audi and see what they think about the change.

Give me a call, we can discuss it more this afternoon.

Best regards, Jim

 

Are you looking to change the wheels or the tires?

I could see putting a narrower tire with a little larger sidewall.

Here is a calc I use:

http://www.miata.net/garage/tirecalc.html

http://marksink.com/tire_wheel_offset/tires.html

http://marksink.com/tire_wheel_offset/offset.html

https://www.rsracing.com/tech-wheel.html

http://www.bigcustomwheels.com/rt_specs.jsp

Edit: just saw that these are 20"s... I can see why you might want to change the wheels. Audi has some std. 18"s that would work perfectly I believe.

Here is a set on Ebay that might fit with Michelin snow tires (Zero feedbacks might be risky)

http://cgi.ebay.com/ebaymotors/Audi-OEM-A8-A6-A4-17-Wheels-Rims-and-Tire-Set_W0QQcmdZViewItemQQcategoryZ43957QQihZ015QQitemZ250195919846QQrdZ1QQsspagenameZWDVW

 

Even though the new wheels you want to use are a narrower width, you want them to have the same offset to keep the trackwidth the same (i.e., keeping the trackwidth the same means keeping the centerline of the wheel/tire in the same place). "Offset" is the distance from the wheel centerline to the wheel mounting surface -- i.e., Offset is ONE HALF the difference between the measured distance from the mounting face of the rim to inner rim edge (A) and mounting face to the outer rim edge (B) [to slightly correct Jim's formula] -- see jpeg.

If the tire is mounted, measure "A" and "B" from the tire inner and outer tire sidewalls to the wheel mounting surface and use the same formula. Offset also has "sign" -- if A is greater than B, this is a "positive" offset (like shown in the jpeg); if A is less than B, this is a "negative" offset.

I can appreciate your project -- I have a front wheel drive Honda with very narrow M&S tires that does great in the snow, and it's really frustrating to be stuck behind a BMW X5 with fat street radials that just can't get going from a stop.
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B is measured between the two vertical lines adjacent to it (I couldn't fit the letter B and the arrowheads inside the vertical lines on the original sketch) -- here's a larger detail that might be clearer.

Yes, wheel diameter has no effect on trackwidth nor offset.
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But there might be clearance issues with brakes / suspension, etc.

 

Dave,
I was about to mention this. Do not buy a smaller diameter set of rims unless you test clearance for the brake calipers (front and back may be different, so check both).

Btw, you shouldn't have any realy performance issues if the tire/wheel combination gives a similar outside diameter and offset.

A good set of snow tires on the stock rims should do fine - a small change in tire/wheel width and/or diamater will not make as large a difference in real world driving as the type of tire you use.

Best of luck,
David

 

Is there a wheel/tire combination from the Flying Spur or Continental GT or VW Phaton that will fit that???