Thread: Really need help with front radius rods.....

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Roger---not to get in a fight--but I think that you are maybe not realizing a couple of facts about these front ends and how we got there--now there is hardly anything similar between ifs and beam axles and only a very minute differance between wishbones, split wishbones, hairpins, and parallel 4 links---

ONE factor with any suspension is that the wheel/axle DOES NOT move up and down, but stays in contact with the ground

Wishbones were split in order to lower the cars back then---

In order to adjust castor beyond what they had (remember they wanted to go from a 40mph car to a 140-200 mph car) they cut a notch out of the arms to angle the axle where they wanted it

The guys wanting lighter weight and more at track adjustment went to tubing HAIRPINS with heims so they cutadjust caster plus set axle square with driveline of car.
A car with hairpins-----does not have any different arc(concentric/parallel) for the top or bottom tube--it works as a singular unit with the batwing on the axle---now a parallel 4 link is a different story.With 4link the caster of the axle has a better chance of staying constant thru out the travel

With the split wishbones, hairpins and parallel 4 links, there is considerable binding of the front on suspension travel and also a greater need to keep the axle centered, especially with anything other than the leaf springs/shackles.

Most of these older vehicles have a decent amount of camber which came about from wheel/tire size height etc and using wheels with different offsets upset the issues very quickly (death wobble)

Originally Posted by jerry clayton

Roger---not to get in a fight--but... ONE factor with any suspension is that the wheel/axle DOES NOT move up and down, but stays in contact with the ground.

A car with hairpins-----does not have any different arc(concentric/parallel) for the top or bottom tube--it works as a singular unit with the batwing on the axle---now a parallel 4 link is a different story.With 4link the caster of the axle has a better chance of staying constant thru out the travel...

Jerry,
As you said, not to get in a fight, but we disagree on a couple of points. First, when we mention movement of the suspension it is relative motion, the measurement of the wheel/axle regerenced to the frame. As you point out, the wheel stays grounded (we hope), but the relative motion of the frame to that wheel is the same whether the wheel & axle move up, or the frame moves down. I agree with your statement, but the relative motion is identical whether we say "...as the wheel moves up & down.." or as the suspension compresses and decompresses." It is common practice to raise the frame/body and then check travel and clearance by moving the axle assembly, right? Same motion, relative to one another - it's only terminology.

Second, we can solve the differential length point easily. Draw a straight line on a piece of paper, and we'll say that's the centerline of the batwing and the back hairpin mount. Now with a compass move out say 3" and strike an arc ~45* above and below that line, and then move out to a 3.25" radius and strike another arc, parallel to the first. On your first arc define two points, say 0.25" above and below the line, representing your "correct" batwing connections. Easy to see that as the frame moves up & down those two points follow that arc, and while the caster changes a bit it is not too much. If you have cross steering bumpsteer is not an issue.

Now using that lower point on the inside arc, connect it to a new point 0.25" above the line, but on the outer arc. This is the batwing connection point for Bearcamp's setup shown - the batwing is effectively rotated on the axle, tilting forward. Now as you move the frame up & down you'll see that in order to stay on the outer line the batwing has to tilt farther back on the upswing - the caster increases faster the more the rods are out of equality in length. It's a simple graphic solution that explains the point.......Or we can just agree to disagree.