ET - CORRECTION

[PDQSHIP@aol.com]

In a message dated 95-11-15 13:20:14 EST, you write:

>
>>
>>Can you tell me what positive offset means? I am confuse! :( 
>>
>>Thanks!

Yo! Scott the info below is backwards, most FWD and AWD cars have NEGATIVE
offset, I'll show you.......
>
>Sure, offset can be one of three measures:
>
>1) zero = hub face is centered at the centerline of the wheel.....  a 6" rim
>with zero offset means that the centerline and the hub centers are exactly
3"
>from either of the outsides of the rim
...... got 1 of three
>2) Negative offset =  hub face is toward the fender (away from the car)....
> a 6" rim with 25.4 negative offset means that the hub face is 1" toward the
>outside of the car from the 3" centerline of the wheel.......  Remember the
>centerline is just rim width divided by 2, and won't change regardless of
>offset.....  Lots of "leaf spring" cars will run negative offset to put wide
>tires inside the fenders...... 
And our audis and fwd cars use this too.........
>
>3)  Positive offset =  hub face is toward the center of the car from the
>centerline of the wheel.....  So a 6" rim with a 25.4 positive offset means
>that the hub face is 1" toward the car from the 3" centerline of the wheel.
> 
>
>Where the confusion arises is when you want to add rim width.....  Let's say
>you go to a 7" wheel.....  If you had a zero offset, you would add a 1/2
inch
>to either side of the rim....  The same holds true if you want to MAINTAIN
>your current NEGATIVE OR POSITIVE offset.  If you have a negative offset of
>25.4 and you want to go to a 7"  rim, you would add 1/2" to the outside rim
>to centerline and inside rim to centerline to maintain the 25.4mm of
negative
>offset.  If you have a 7" rim on a POSITIVE offset of 25.4, again you would
>add a 1/2 inch to the outside to centerline and inside to centerline
>distance....
OK that one is ok with some deletions......
Let's change this below to make it right

>PROBLEM:   I can't add 1/2 inch to both the outside and the inside of the
>rim, cuz the rim hits the steering arm, what do I do?   Change the
>offset.....  So you have a 6" wheel that basically just misses hitting the
>steering arm with a 25.4mm NEGATIVE offset....  Well if you go to a 7" wheel
>with a 12.7mm NEGATIVE offset, the inside rim will be positioned exactly
>where the 6" wheel inside rim is with a 25.4 offset (25.4 - 12.7 =
>12.7mm)....  You have effectively added the width of one inch to the outside
>of the rim and left the inside rim in the same location as your old
>wheel......  Make sense? Yea right....
>
>You can easily tell if your increase in rim width will require an offset
>change....  Just take a wheel (tire on, this could be the prollum more than
>the rim) and look closely how tight the gap is between the wheel/tire and
the
>first obstruction (it's usually REAL tight in there, like a 1/2 inch)
measure
>that, that is how much width you can add to the inside to centerline
distance
>when going wider.....  Let's say its a 1/2 inch clearance with a 6 inch rim,
>45.0mm neg offset, on a 205/60 tire, and you want to go to an 8in rim with
>the same tire ......  So basically, you can add 1/2
>inch to the  inside rim, and will need to add 1 1/2 inches to the outside
>rim.......  Your offset is 32.3, but now you need to watch
>your fender clearance, cuz you pushed the rim 1 1/2 inches toward the
outside
>of the car instead of 1/2 in the 7" rim example above.....

REALITY AND FACTS
Per audi ur-q----  The 6 inch rim has an offset of 45mm negative, the 8 inch
wheel option has a 24mm negative offset.....  That means that from a six inch
wheel you can go toward the strut exactly 4.4mm (according to audi) befores
something gets critical (difference in wheel width/2 - offset change = inner
wheel rim location in relation to stock OR 
50.8mm/2 = 25.4mm - 21mm = 4.4mm of 50.8mm rim gain heads toward car)......
THAT means that of the 2inch gain, you are putting only a fraction of that
gain into the wheel, the rest is heading toward your fender, increasing track
and bearing failure rate......

Also know of one netster that has done a 16X7.5 swap on an ur-q with a 35mm
neg offset wheel, and it seems to work, so audi is conservative with the
numbers, it looks like this:
38.1 /2 =19.05mm -  10mm = 9.05mm of 38.1 rim gain goes toward car..... So it
looks like audi said what is the best case and went with half that, sounds
right.....

>Confused?  Draw a rim 6" and one 7" above it and one 8" above that, draw the
>centerline so that they all match.  Then put in your offset (most audis are
>35-45mm negative) line, then look what you need to do to that offset when
you
>try to get the inside of the rims to line up.....  Maybe easier to
understand
>this way.
>
>HTH

Well you didn't ......  Anyone need any clarification, I can flame myself
too.....  Humble apologies for the opposite day enaction, should have had
coffee first.....  Must be all those six's running around in my head.....
   Really tho, please post me if you need help with this, it isn't as
confusing as I might have posted, and I can simplify it to those who didn't
follow......  thank goodness all I had was the negatives and positives
backwards on ET, not the battery....

Scott