Scott-
Wheel and tire choice is fun systems engineering! If you're thinking of
changing wheel parameters like mass, diameter, width, offset, etc., it's
worthwhile to review books on suspension design or wheels and tires first.
Good reading includes "Tune to Win" by Carroll Smith (pretty comprehensive
suspension tuning), "How to Make Your Car Handle" by Fred Puhn (a short
course, including tables of wheel data for various car models), and
"High-Performance Wheel & Tire Handbook" by Jim Horner (consumer-oriented
wheel & tire stuff).
Here are some examples of things to think about: Besides static and dynamic
clearance, something to consider with respect to offset and backspacing is
the resultant loads on wheel bearings. Negative offset gives good load
distribution between inner and outer wheel bearings in straight-line driving,
but results in higher proportional loading on inner bearings during
cornering. In general, when going to a wider wheel, it is good to maintain
your stock offset by increasing both backspacing and frontspacing equally.
When changing wheel and combined wheel-tire diameter, things like unsprung
mass, polar moment of inertia, and change in vehicle center of mass are
important and should be examined in light of the car's uses and your
priorities (e.g. highway use, mileage, wear, acceleration, handling). This
is merely the tip of the iceberg.
Just my $0.02 :-).
your humble fellow SOL-
Paul Geithner
Arnold, MD
NASA-Goddard Space Flight Center
'78 Spitfire
'71 Corolla
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