Bill:
You are absolutely right about the bump steer. I spent two weeks
adjusting to bump steer out of my TVR (that included the time for machining
new parts). I am amused at Carrol Smith's instructions on measuring bump
steer with a dial indicator. I had to measure mine with a yardstick! The
final solution was to raise the end of the tie rod at the steering arm 1/2",
but I had to redesign the tie rod end assembly to do it. As to
over-springing to stop bump steer, I quote Fred Puhn: "If it can't move, it
can't bump steer". A friend of mine in England races a TVR Tuscan and uses
800# springs in the front. He says some of the Griffith guys have gone to
1000# springs.
John
> You can affect bump steer by raising or lowering the rack or moving it
> forward and back. You can also affect it with changes to the steering arm
or
> tie rod length, but that's harder.
>
> Zero static bump steer happens when the pivot ends of the tie rod are in
> line with an imaginary line drawn between the upper and lower suspension
> pivots at both ends, and the angle of the tie rod enables an imaginary
line
> drawn through it to intersect with the instant center (the intersection of
> lines drawn through the suspension arms extended to an imaginary point).
You
> can see that moving any of these elements (suspension points, tie rod
pivot
> locations, angle, and steering arm length) will all affect bump steer.
>
> You basically have to fiddle until it's close to zero within the range of
> typical suspension travel. It's absolutely magic what eliminating bump
steer
> does to a car. I'm convinced the biggest reason people spring vintage race
> cars so hard is so they won't bump steer. They won't handle for beans
until
> it's eliminated, and really stiff springs make it seem like the car
handles
> better even though all it's doing is keeping the bump under control.
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