general bumpsteer question

At the bottom of that page is a diagram - that's the best way to look at it.

From the front of the car, look at the spindle. As it goes up and down, it travels in an arc. The upper and lower arms both travel in their own arcs, but because the spindle is attached to both of them, and they're different lengths, the steering arm travels in it's own arc. The tie rod has to be adjusted so it will exactly match the steering arm's arc.

In reality, the steering arm travels in an eliiptical pattern, not a true arc, but the tie rod DOES travel in an arc, so you can't adjust it perfect, only very close.


If you look at the longacre diagram, notice that if you raise or lower the rack location, the width of the inner pivots needs to change, as does the length of the tie rods, to match the intersecting lines. You only need to be close, so don't worry about custom-width racks and stuff, just take care in measuring the bumpsteer with what you have, and then adjust something and check it again. It only takes a few tries to get a feel for what's happening and then you can make smaller and smaller adjustments until you're as close as possible. For the most part, you're probably not far off to begin with, and chances are your only option is to adjust the height of the outer end, so you won't have much trial to get it whittled down.

It's kinda like adjusting carb jetting - make a single change and see what happens, then go from there.

Heck, I don't know what thread sizes I have... it's all aftermarket replacement parts for an OEM 74 Dart suspension.  Tie rod sleeves are TRW's that are thicker in the middle, but taper down to the smaller A-body ends.  Kind of a hybrid C-body tie rod end arrangement.  I need to go measure some of that stuff, since I think I have a lot of it on the shelf already.

This might be as good a time as any to upgrade my tie rods, although it's all new stuff with only a couple thousand miles on it.

Here's a shot of the OTRE / wheel interface:


Looking at it, I think if the Heims are significantly thinner than the OTRE (up-down, not just side to side), that alone might let the wheel sneak past the OTRE...  Curiouser and curiouser...

Clair

I considered making a tie rod with heims on both ends, so both ends of the link could be height-adjustable. The Mopar suspension has a one-way toe curve - I'd have to look again at the charts to remember which way it goes, but for instance, at full compression it's at a toe-out condition, and as the wheels fall, it toes inwards all the way to full rebound - it may be the opposite of that. So from ride height to compression, the wheels hit a toe-out condition, but during rebound, they toe-in.

In contrast, just to clarify the picture in your mind, the Alterk is at the apex of it's toe curve at ride height - the toe curve is toe-in from that point, in both directions.

I was thinking if both sides of the tie rod were height-adjustable, you may be able to cancel some of the goofy in and out curve the stock stuff had. I haven't had a chance to try it in the software to see what changes would straighten it out, if it even would help at all... I'm SLOWLY getting more tests done on the stock suspension, but I have to fit it in between the welding, so it's taking time. Definitely worth it though. Just the spindle tests alone have been immensely interesting.

i completly forgot about this, until i had to look up some info. thansk for all the tech bill, ive asked a few other sites (like rx7 specific, and v8 rx7 boards) and all i got was a bunch of beating around the bushes, no actual help.

i think im dropping my engine cradle 5/8 of an inch and buying the bumpsteer correction kit from a guy that makes them for the 3rd gen rx7. im still debating on pulling the engine cradle forward an inch or so.

here is a picture of my setup so far.

ignore some of it, still a work in progress. thats with it dropped ~5/8 of an inch, moving it forward an inch or so would give me much more room i think room for ear where starter bolts to and probably brake booster room) .