Gene:

The closest I came draw this out is

Suspension upward movement: .0602" toe in

Suspension downward movement: .0783" toe out


This is only an approximate as I would need quite a few other measurements taken very accurately to get it exact.


Recommended bump steer is .005-.015" per 1" of suspension movement. But even more of a concern is that it is going from toe-in to toe-out.

If a car has iniitial alignment settings of toe-in (as street cars do) you want the bump steer to toe-in only.

If a car has iniitial alignment settings of toe-out (as race cars do) you want the bump steer to toe-out only.

By doing both, the car will have a twitchy feeling to it and will show more rapid tire wear.


Pete

 

Pete, when you all say 'Bump steer' you mean the direction of wheel change on the UPSWING?? so if you pass over a curb, say...lifting one wheel...i'ts the direction the wheel points when lifted only??? NOT including the direction it points when lower than level?? say in a hole??
the way mine is...if it's in a hole...it would point in up to a point, then out again..slightly at end of suspension travel...
when pushed upward, it's pulled to a toe out position....

The way I see it, IF the inner tie rods were all the way lower than the knuckles at ANY suspension height...with a rear steer car like ours...the effective length of the tie rods would allways be shorter, and pull the wheels in at the rear...or toe out....
if the inner ends are neutral to suspension setting, the wheels would be set for the most toe in they ever could see...as going up or down would cause toe out.....
if the tie rod ends are all the way up in the air...above highest point of suspension...the further the wheels rise, the more toe in as the effective length is shortened and the wheels forced to tow in positon....but if

seems to me no matter where the inners are set, the wheels have to change toe in and out and that amount would be more dependant on tie rod length and the knuckle length....

my primary concern is excessive tire wear....
what sort of recommendation you have on this...and what percentage gains would your solution do?? I know you can't predict tire wear as a final figger, but as a percentage of overall numbers?? ok??

GENE

 

Gene:
The term "bump steer" refers to the amount the wheel will toe-in or toe-out through suspension movement wether the suspension is moving above ride height (tire moving into the fender well or nose down) or below ride height (tire moving out of whell well or nose up).

A properly designed steering geometry can be made to have near zero bumo streer. To do this the following has to be done on a un-equal lenth double a-arm suspension.

The outer tie rod end has to align with an imaginary line from the upper ball joint through the lower ball joint.

The inner tie rod end has to align with an imaginary line running from the upper a-frame pivot to the lower a-frame pivot. (this is the problem with a center take off rack)

With rack and pinion the tie rod has to run parallel to an imaginary line from the lower a-frame inner pivot to the lower ball joint pivot.


When these condition are met then the suspension will have zero bump steer in both up and down movement.


The problem with a center take off rack is the tie rod length. We can't change that. That is why C-4's have end take off racks.

But we can try to get your tie rods to run closer to parellel to the lower a-frame. This will have to be done by either lowering the outer tie rod or raising the inner tie rod. You will have to look at your set-up to see which will be easier. The amount we will have to move them is 1 1/2"

Anytime the toe setting is allowed to go over-center from toe-in to toe-out the wheel will get a slight flutter to it causing tire wear, twitchyness and poor steering feel.


Pete




[Modified by Pete79L82, 8:33 PM 3/14/2003]

 

Pete, that is why in my first consideration I was looking for an end take off rack, but in fact never located one what would fit in there and be long enough on the tie rod ends to afford a long swing arch....long enough tie rod end...not with enough to turn the wheels any, that is....so the CTO was used....I should have raised the inner tie rods as was thought of by steeroids, but I didn't want to re machine any steel adaptor blocks...at this point, I suspect I will have to do something....oh well, live and learn....
I suppose I could change the angle of the rack tilt, and gain it that way...but that would make a mess out of the input linkage....too much angles, needing another joint....similar to steeroids setup....humm....think I"ll get my buddy to reweld something...

Thanks for your input, and upon looking/thinking of what you are saying....I see what is rong and why.....thanks for your time and effort....

edjemakatiion is hard....

GENE :D :D :cool: :cool: :cheers: