James writes:
>i never understood the rotating tires business...
Here's some general observations from what I've experienced over the years:
When you start out with a new "set" (same brand/spec, even if different size
F/R) of "R" tires, all corners of the car can have the same (potential for)
traction. If the car has acceptably balanced handling, once the new tires
are adequately scrubbed-in and heat-cycled, the car may be at its best, or
close to its best, performance level. If the tires either wear at a greater
rate and/or see greater heat on either end of the car, then the end of the
car "working" the hardest will loose traction quicker than the other end.
Therefore, rotating tires front-to-rear (when all are same wheel/tire size)
and, if necessary, side-to-side to equalize wear and heat exposure, will
tend to keep the handling balanced for a longer span of the total tire life.
The total grip will, eventually, be reduced as the tread rubber gets both
harder and thinner but, as the tires wear, the changes in handling balance
will not be as pronounced as they would be without rotation. However, at the
end of tire life as overall traction falls off, that once "balanced
handling" car will understeer going into turns and oversteer comming out of
turns.
>you replace in pairs anyway right?
If you replace "in pairs" you run the risk of unbalancing the car's
handling. Again, after the new pair is "adequately scrubbed-in and
heat-cycled", the end of the car with the new tires will, most often, have
better traction than the end with the older tires. New tires on the front,
car loose; new tires on the rear, car pushes. Now, if the car has adequate
and easilly accomplished bar/shock/toe adjustment ranges, along with
possible tire pressure changes, the handling changes can be "chased" through
the un-even wear rate/life of the tires to maintain handling balance. Trust
me here, this "game" requires a real art (and some luck) in order to be able
to, regularly, pull-off this feat.
When the car has different tire/wheel sizes/offsets on each end AND wears
and/or heat-cycles one end quicker than the other end then, obviously, the
rotation "fix" won't work. In that case, as with my current AS '96 GS, new
tires, most effectively, get introduced either as full sets in advance of
"important" events or get introduced as new or fresher pairs to the
higher-usage front end of the car before the traction imbalance is
excessive. Additional wheels are necessary to be able to maintain this kind
of traction balance through "platooning" pairs of fronts.
>the one thing that can be helpful on stock suspensions with
>inadequate camber or roll control is to swap them so the "fresh" edge that
>was to the inside of the wheel is now on the outside
Not just stock suspensions, but on any car where the optimum, or best
possible, set-up wears either the inside or outside edges at a greater rate.
BTW, this only works if the tire's casing (not tread pattern) has a
symetrical design. For example, the BFG R-1 226s and 230s (predesessors to
the G Force) could not be "flipped" as their casing was asymetrical. When I
was running bias-ply Hoosier "Autocrossers" on my '85 SS Vette, I not only
followed the front-to-rear rotation discipline but by making regular tread
wear measurements would pick a point about half way through the tires' life
to flip the tires inside-out on the rims. I determined that the additional
cost of the re-mounting was significantly less than the value of the
additional extended "life" (total run time) of a set of tires. However,
after "flipping", it took a few runs to re-scrub the tires before getting
back to some decent traction.
Don
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