Suspension Optimization and Tuning Help

[AutoX_a_Truck?]

Ron, I got your message so I figured I would check in even though I do not have much of an update. I am glad to see you are back on the forum, and I hope that your business venture is going well. I have not been home or had time to work on the Scout since February as I have been very busy with school, which is finally winding down after 20+ years. Once I graduate in mid-May, I should be able to devote some more time to the Scout. In the meantime, my Dad has tweaking the steering geometry and other components to get bump steer under control. I will also have the opportunity to attend two autocross events on June 1 and June 29 for gathering more testing data and video footage. Before I start, I had a carryover question from a previous post:

16. Also mentioned earlier ...
The final ... but BIG issue, is your front shock valving doesn't have enough low-speed rebound. Meaning the front shocks let the inside front suspension roll too much and come up too quick when you step off the brakes. To achieve your AutoX goals, you need front shock valving with both stiffer low speed rebound valving & some degree of rebound valving at zero, before it moves.

Ron, I forgot to ask this earlier . . . What sort of inputs of measurements, video footage, or other inputs are necessary to determine shock valving? And for the upcoming events are there any video angles or data I should focus on collecting?

#4 - If you're not moving the steering box, arms & centerlink assembly back the same amount ... that will reduce the ackerman ... so it requires more ackerman be built into the spindle offset. Moving it in 2" may be overkill. Realize the centerlink adds some ackerman as it moves forward during steering (as the steering arms rotate).

You need to either calculate it out or test it physically on the truck. If you turn the wheels left ... and make the RF at a 25° angle ... what angle is the LF at? I often target 4-5° more.

The results were as you indicated above. With the wheels turned to the left and the RF at a 20° angle, the LF is also at a 20° angle (+ or - 1°). However, by further modifying the steering arm, the results improved and are closer to the target of 4-5°

#8 - Either the ball joint measurements are off or the caster measurements are off, because they don't match. Double check & see if you can find which is correct.

I still need to set everything up for re-measuring the ball joint dimensions.

#13 - Doing the bump steer could show a small or big problem. So good it's on the to-do list.

The tie rods were pointing above the instant center, which caused the wheel to bump-out when moving up, and bump-in when moving down. Using a very helpful Longacre document and a different centerlink, it was possible to get the bump steer under control using a design similar to the bottom diagram. For the time being though I do not have super accurate measurement numbers.



Here is a pic of the centerlink in mock up and a pic of the final product.

#15 - You've already done something to improve this ... by switching to a larger front sway bar. Without running the calcs, we don't know if these achieves the optimum front to rear roll angles. And if you're going the low roll angle route, a decision to make is "how far". Lt's say the 33mm bar reduces your roll angle from 3.0° to 2.5°. Do you want to fine tune that combo? ... or go to a bigger splined sway bar in the front and shoot for a roll angle of 2.0°, 1.5°, etc? ... and tune your spring & bar package around that?

I probably would prefer to look into further reducing the roll angle with a larger splined sway bar if the 33mm sway bar only reduces the roll angle to 2.5°. I largely base this off information in some of your other posts, and under the assumption that you think it would be a “good” idea to further reduce the roll angle. In the past, I looked into a larger splined sway bar from Speedway Engineering. I think it would be a relatively affordable way to upgrade the sway bar and build in greater adjustment. The main problem will be packaging. If a larger splined sway bar is placed in the same position as the stock style sway bar, it might require arms with multiple complex bends to fit because the packaging is rather tight. That said, I think it should be feasible to fabricate a solution, and once the initial fabrication was done it would be relatively easy and affordable to fine tune the sway bar in the future.

This from an earlier post:

17. As you correct all these things to make the truck turn better ... if nothing is done in the rear, you'll lack forward bite off the corners. Two things that will need to be addressed are shock valving (stiffer low speed rebound) and the height of the IC for "lift & plant" leverage.

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I apologize up front, because once again I am potentially opening up a new can of worms . . . But once the front end is in a happier place, my Dad and I thought it might be time to look at redesigning the rear suspension. When we first built the chassis it was a “use what we had on hand” project, closely followed by a “go with what is easy to package and fabricate” motto. I figure it should not be too hard to package a homemade offset 3 link for the rear that can offer more adjustability and less unsprung weight among other attributes.