Tire sizes for urQ!? (longish)

[Richard Funnell <rfunnell@pobox.com>]

Tire people,

I'm starting to think about bigger sneakers for my '83 urQ, and have a few
questions.  

Late one night I worked out a spreadsheet to calculate the rubbing and
radius effects of using larger wheels and tires.  When I finished, I
remembered a similar effort by Eric Fahlgren (Dec 23), dug up his formula
and compared it.  The difference is I don't include the first factor in his
formula, wheel width affecting the tire width.  I think in many cases, that
will end up double counting, especially if choosing a matched tire and
wheel combination.  I then stuffed in all the combinations from Andrew
Finney's list of urQ combinations (recently resent by him on June 8) and
tried to draw some conclusions.

There were some apparent inconsistencies between actual and calculated, but
it appears that there is virtually no additional room on the inside of the
tire, and up to 20mm max additional clearance on the fender side based on
specific sizes known to fit.  (I then crawled under my car to verify this,
and it isn't at all obvious, which does nothing to improve my confidence in
my numbers but then life is never perfect.)

Calculated good combinations (right at the edge) end up as: 

-	225/50 16, ET 35
	- same inside clearance as stock 206/60 15, ET 45
	- 20mm closer to the fender
	- 0.7% larger radius (in the noise)

-	225/45 17, ET 35
	- same inside clearance as stock 206/60 15, ET 45
	- 20mm closer to the fender
	- 1.2% larger radius (still in the noise)

In both cases this fit will be so close that variations in tire design will
make it or not, and rolled fenders may be needed to be sure.  Rolled
fenders seem to allow at least an extra 6 or 7 mm, which seems logical
looking at the lip.  In either case, going to a 215 tire and ET 40 wheel
should be a slam dunk, since that reduces the fender side increase from
20mm to 10mm.  

So, the questions:

-	Do these calculations seem to agree reasonably well with listers'
experiences?  I'd be happy to post the results of any comments, hopefully
with indications of whether bad combinations rubbed on the inside or the
fender side.

-	Does anyone know a good body or other shop in the Bay area that has
rolled fenders before without messing up the paint?  How much does this
usually cost?

Thanks all.

Richard
'83 urQ