Offset rack bushing actually increase the chance of bumpsteer. Maximum Motorsports has discovered that it is best to use non-offset bushings. I would confirm you actually have bumpsteer. Does it change direction when you hit a bump? If not then you may not have bumpsteer. Does it wander? Another words does the vehicle tend to wander and do you have to constantly make steering corrections? If so then you may need to increase your positive caster with a set of caster camber plates. Increased caster will increase directinal stability and stop steering wander. I have found many people get confused with bumpsteer and steering wander.
This is from Maximum Motorsports
BUMPSTEER
Bumpsteer is the term for the toe setting of a wheel
changing as the suspension moves up and down
over bumps, or with body roll while cornering.
There is a widespread myth that the tie-rod should
be kept parallel to the ground to avoid bumpsteer.
THIS IS NOT TRUE! What IS required is for the tierod
to be kept parallel to the lower control arm. That
way, as the suspension moves, the arc of the ball
joint and the arc of the tie-rod end do not transfer
any steering input to the spindle. As the car is lowered,
the tie-rod end and the lower control arm move
together, staying parallel. If offset steering rack
bushings are installed on a stock-geometry Kmember,
the tie rod end and the lower control arm
will no longer be parallel. Installing offset rack bushings
will INCREASE the amount of bumpsteer.
Ford engineers have actually done a very good job at
minimizing bumpsteer for a typical street-driven car.
Specifically, the bumpsteer was designed to cause
the front wheels to toe out during bump. This is a roll
understeer condition; the outside loaded tire will turn
to the outside of a corner as the body rolls. A car that
has a basic tendency towards understeer is more
stable and predictable. That predictability makes for
a safer street car.
Competition cars using stock K-member geometry
can benefit by fine-tuning the amount of bumpsteer
with an adjustable tie rod end kit. The MM Adjustable
Tie-rod End Kits provide an assortment of spacers,
in .015" increments, to help position the-rod end at
exactly the correct height. Adjusting bumpsteer on a
particular Mustang also allows correcting for individual
differences in suspension geometry caused
by production tolerances.
Offset rack bushings DO have a use, and are
beneficial if the inner control arm pivots have been
moved from the stock location. On MM K-members
the pivots have been moved upwards from the stock
height. In this case, raising the steering rack will help
match the geometry of the raised inner control arm
pivots, and reduce the required height of the
bumpsteer spacer stack at the spindle.
If offset steering rack bushings are used, they
should be made of aluminum. Polyurethane offset
bushings do not work. The urethane has too much
“give”, making it impossible to get the rack mounting
bolts tight enough to prevent the rack bushings from
rotating during hard cornering.
This is from Maximum Motorsports
BUMPSTEER
Bumpsteer is the term for the toe setting of a wheel
changing as the suspension moves up and down
over bumps, or with body roll while cornering.
There is a widespread myth that the tie-rod should
be kept parallel to the ground to avoid bumpsteer.
THIS IS NOT TRUE! What IS required is for the tierod
to be kept parallel to the lower control arm. That
way, as the suspension moves, the arc of the ball
joint and the arc of the tie-rod end do not transfer
any steering input to the spindle. As the car is lowered,
the tie-rod end and the lower control arm move
together, staying parallel. If offset steering rack
bushings are installed on a stock-geometry Kmember,
the tie rod end and the lower control arm
will no longer be parallel. Installing offset rack bushings
will INCREASE the amount of bumpsteer.
Ford engineers have actually done a very good job at
minimizing bumpsteer for a typical street-driven car.
Specifically, the bumpsteer was designed to cause
the front wheels to toe out during bump. This is a roll
understeer condition; the outside loaded tire will turn
to the outside of a corner as the body rolls. A car that
has a basic tendency towards understeer is more
stable and predictable. That predictability makes for
a safer street car.
Competition cars using stock K-member geometry
can benefit by fine-tuning the amount of bumpsteer
with an adjustable tie rod end kit. The MM Adjustable
Tie-rod End Kits provide an assortment of spacers,
in .015" increments, to help position the-rod end at
exactly the correct height. Adjusting bumpsteer on a
particular Mustang also allows correcting for individual
differences in suspension geometry caused
by production tolerances.
Offset rack bushings DO have a use, and are
beneficial if the inner control arm pivots have been
moved from the stock location. On MM K-members
the pivots have been moved upwards from the stock
height. In this case, raising the steering rack will help
match the geometry of the raised inner control arm
pivots, and reduce the required height of the
bumpsteer spacer stack at the spindle.
If offset steering rack bushings are used, they
should be made of aluminum. Polyurethane offset
bushings do not work. The urethane has too much
“give”, making it impossible to get the rack mounting
bolts tight enough to prevent the rack bushings from
rotating during hard cornering.