Upper link location on triangulated 4 link question?

[jercars]

I looked around old threads and haven't been able to find what I'm looking for. I'm setting up my 68 Charger with a 600 HP Hemi and will weigh around 4000lbs. Art Morrison builds many of their rear systems with the upper link mounting to the front of the axle housing rather than above it. Wouldn't that be less stable and more prone to axle rap? I'm new to chassis design and I'm running into clearance issues and the front mount design would help me but I'm not sure if that will cause problems during hard launches. Art knows what he's doing so I would imagine it's fine but I definitely wanted to check with you guys and see what kind of pros and cons I'm facing. Thanks

[Ron Sutton]

There are no strength issues with that mounting location. It is merely a function of distributing the housing's rotational torque between lift & push forces. Rear suspension devices are simply levers to utilize the housing's rotational torque to lift & push the chassis forward.

With any rear suspension, we need some balance of lift & push. More lift & less push plants the tires harder, but for shorter distances. Less lift & more push plants the tires softer, but for longer distances. Too much lift … with high power … creates violent tire & suspension conditions. Too little lift … with lower power … creates easy wheel spin. What ratio of lift & push a given car needs is dependent on tires, weight balance, corner exit speeds, track grip, CG, weight transfer, power output, gearing, etc, etc.

Many people only look at the Anti-Squat percentages to define this, but A/S is only one of a dozen factors in how the housing's rotational torque is utilized to define the traction capabilities of a car under acceleration.

In general, the upper links "pull & lift" while the lower links "push", but there are variables. The factors that determine "how much" each does, are:
a. Vertical distance of the link housing pivot from the axle centerline.
b. Horizontal distance of link housing pivot in front of, or behind, the axle centerline.
c. Angle of the links.
d. Corresponding Instant Center (IC) height & distance from the axle centerline (determined by the angle of the upper & lower links).
e. Lift point* of the rear suspension levers.
* This is the IC with multi-link suspensions. Torque arms & truck arms lift point are the actual contact point.

I've listed a simple guide below on the effects.

To create more lift with upper links:
* Locate the upper link housing pivot(s) higher, farther away from the axle centerline.
* Locate the upper link housing pivot(s) farther behind the axle centerline.
* Increase the angle downhill (going forward).
* Shortening the distance of the IC from the axle centerline.
* Raising the IC.

To create less lift with upper links:
* Locate the upper link housing pivot(s) lower, closer to the axle centerline.
* Locate the upper link housing pivot(s) farther ahead the axle centerline.
* Decrease the angle downhill (going forward).
* Lengthening the distance of the IC from the axle centerline.
* Lowering the IC.

To create more push with lower links:
* Locate the lower link housing pivot(s) lower, farther away from the axle centerline.
* Locate the lower link housing pivot(s) farther behind the axle centerline.
* Increase the angle downhill (going forward). (See note below)
* Lengthening the distance of the IC from the axle centerline.
* Lowering the IC.

To create less push with lower links:
* Locate the lower link housing pivot(s) higher, closer to the axle centerline.
* Locate the lower link housing pivot(s) farther in front of the axle centerline.
* Increase the angle uphill (going forward). (See note below)
* Shortening the distance of the IC from the axle centerline.
* Raising the IC.

IMPORTANT NOTE: The lower link angles determine the rear steer scenario for the rear suspension.
* Level lower links create a neutral rear steer scenario as the car achieves roll angle.
* Angling the lower links uphill (going forward) increases “lift” but adds positive rear steer as the car achieves roll angle.
* Angling the lower links downhill (going forward) decreases “lift” but adds negative rear steer as the car achieves roll angle.

So, in your case, where the upper links are mounted low (closer to axle CL), and in front, that will have a little less "lift" than if the upper links were mounted higher & centered over the axle housing. You may find this works excellent. Or you may find you need a little different balance of lift & push and need to tune on it. There are many ways to skin the cat. Just use the guides above.

[jercars]

Ron I've stumbled onto a few of your posts in the past and I was just wondering if they let you autograph the space shuttle after you built it? All kidding aside you answered all my questions perfectly and I can't tell you how much I appreciate your input and willingness to share your knowledge. Thank you very much

[Ron Sutton]

Ron I've stumbled onto a few of your posts in the past and I was just wondering if they let you autograph the space shuttle after you built it? All kidding aside you answered all my questions perfectly and I can't tell you how much I appreciate your input and willingness to share your knowledge. Thank you very much

:lol::lol::lol::lol::lol:

Glad I could help. Best wishes.

.