I've been using
http://www.thesamba.com/vw/forum/viewtopic.php?t=298574 to figure out
my 'other' wheel/size issues Some good information there with
drawings and measurements and all that useful stuff.

Rob
becida@comcast.net

At  10/30/2011 04:56 PM, BenT Syncro wrote:
>Hi Ken,
>
>The trouble I find with using "backspace" is people either use a
>calculated measurement whilst others physically measure the wheel.
>One or the other frequently do not take into account that wheel size
>often does not take the dimensions of the area past where the bead would seat.
>
>Anyway, here's how I read your wheel. ET42 at 7.5" wide compared to
>a factory alloy wheel of ET30 at 6.0" wide. On the inside edge, you
>are likely to see the inner edge move inwards 31.05mm compared to
>stock. That's 12mm for the offset difference plus another 19.05mm
>(0.75") because of the wider wheel. You will have clearance issues
>unless you correct the offset with spacers as you already surmised.
>
>You could get away with a range of spacer thicknesses depending on
>what you what to accomplish. Personally, i would adjust to the
>factory offset of ET30 w/ 12mm spacers. You will need
>proportionately longer bolts up front and longer studs in the rear
>unless you have a big brake kit with studs in front. If you do, then
>longer front studs are also in order. Don't forget that you will
>need to factor in the thickness of the wheel mounting pad unless you
>recontour the lugholes to a 60 degree conical seat. An alternative
>would be bolt on spacers which have studs.
>
>There will be .75" more wheel on the inside and outer edge.
>Suspension geometry should be unchanged. You should be able to clear
>the steering components. The downside is you will have more 'splash'
>from the tire compared to stock. Tire selection can become critical
>if you go to a larger offset depending on sidewall bulge.
>
>On the upside, thick spacers often make up enough distance between
>the tall 2wd dust cap so machining the centerbore might not be needed.
>
>
>
>BenT
>sent from my electronic leash
>
>On Oct 30, 2011, at 1:32 PM, "Ken Lewis" <kdlewis@northstate.net> wrote:
>
> > Two wheel drive DOKA.
> >
> > Offset is 42. I arrived at the back spacing by dividing the
> width, 7.5"(190.5mm) by two and adding the offset. A formula I
> found in the Vanagon archives. I "assumed" it to be correct.
> > Ken
> >
> >
> > ----- Original Message ----- From: "BenT Syncro" <syncro@gmail.com>
> > To: "Ken Lewis" <kdlewis@NORTHSTATE.NET>
> > Cc: <vanagon@GERRY.VANAGON.COM>
> > Sent: Saturday, October 29, 2011 3:32 PM
> > Subject: Re: An interesting article on gas mileage vs wheel size
> >
> >
> > Putting on a 2wd? Do you have the offset rather than a measured
> or calculated backspace? It's the figure that says 'ET' followed by
> a couple of numbers. I'd like to help but don't want to rely on the
> expression of offset as backspace because accuracy can be affected
> by how you arrived at that number IMHO.
> >
> >
> >
> > BenT
> >
> > sent from my electronic leash
> >
> > On Oct 29, 2011, at 9:43 AM, Ken Lewis <kdlewis@NORTHSTATE.NET> wrote:
> >
> >> I found this article while researching what it would take to get 17"x7.5"
> >> Audi A4  wheels to work on my crewcab.
> >>
> >> This line caught my eye;" What's immediately apparent from the results is
> >> that as the wheel-and-tire packages get larger and heavier,
> acceleration and
> >> fuel economy suffer. Neither is a huge surprise, but we measured a
> >> 10-percent drop in fuel economy and a four-percent degradation in
> >> 0-to-60-mph acceleration from the 15s to the 19s".
> >>
> >> I  looked at  these this morning.
> >> http://winstonsalem.craigslist.org/pts/2618213904.html . Nice looking BIG
> >> wheels. Some road rash. He also has the longer lug bolts.
> >>
> >> The bolt hole size is good but it appears the center bore
> (~57mm) would need
> >> to be opened up. I need to actualy take a front wheel off my truck and do
> >> some measuring . I have read the grease cap can be shortened to get rid of
> >> the lip.
> >>
> >> I arrived at a  back spacing of 137.25mm on the Audi wheels . By my
> >> calculations I would need a 14mm spacer? Anyone?
> >>
> >> Thanks Ken
> >
> >