Total Lateral Load Transfer Distribution

[Sleeper68]

I mean, as a mechanical engineer, you could just break out your old beam calcs and find out that there is absolutely no way that arm is flexing 0.2" without breaking. It'd have to be significantly thinner to withstand that kind of deflection. And that's a single turn - no chance it'd survive even low cycle fatigue.

Olds,

I understand your point. As stated previously, 0.2" refers to the total displacement (both loading directions, 0.1" from center) of the zerk fitting on the bottom of the outer tie rod end. This means that the zerk fitting moved about 0.1" from the unloaded position in both directions. This also means that the steering arm itself did not move the entirety of this distance. I did not measure steering arm deflection at any point. Additionally, as mentioned previously, this test procedure was not very robust and the likelihood for error is high. A test will be performed soon with a more robust procedure. I agree 0.2" steering arm movement does not pass the smell test. The reality is the steering arm does not move that much, the zerk fitting at the bottom (end) of the cantilever moves half that much (maybe). The steering arm furthest point probably moves more like 0.040-0.050". Regardless, this will be fleshed out with a proper test soon.

By measuring to the tie rod, you're including that rod end joint in your slop. Seems far more likely to have a bad tie rod end than a steering arm flexing that much. Either that or the steering arm isn't actually tight against the spindle, but that would likely be catastrophic and very obvious.



Video would be good.

The likelihood that there is any slop in the outer tie rod end is very low, in my opinion. The reason I believe this is because the outer tie rod end is made by Howe and has a user set pre-load or lash. I set the rod end up with some preload (as recommended by Howe). There certainly will be some flex of the rod end stud, however. It is approximately 5/8" in diameter and is made from alloy steel. The bolts attaching the steering arm to the spindle are 1/2-20 grade 8 and all are tight.

I have attached a few pictures of the modified steering arm including the outer tie rod end and the wheel for reference. You will be able to see that the rod end is very low near the wheel. Deflection at the bottom zerk fitting will be about double of the deflection of the steering arm lowest point.

[Sleeper68]

There is a new development in the understeer saga. While underneath the car checking fasteners, I found that my rear sway bar was cracked. Pictures attached below. I am uncertain when this happened. The car has not really been driven since the last SCCA event on 09 October 2022 (video: https://youtu.be/sAUohwkN96A). I think crack started to significantly open up during the run in this video. You can see that car yaw fairly well early in the run, but at 0:43 I start a higher speed right hand sweeper. In the previous 4 runs, I was able to stay off the cone wall to the left by about 2 feet, but on my fifth run (shown in the video) I push out and hit a cone in the wall. SoloStorm data shows cornering G's to be comparable, as well as corner entry speed. Max corner accelerations for run 4 and 5 were 1.05 and 1.00 g respectively. Corner entry speeds for run 4 and 5 were 54.1 and 53.3 mph respectively.

The car was able to make counter centrifugal force, but it wasn't able to maintain the correct arc at the same speed. My current hypothesis is that the rear bar failed just before, or going into this turn on run 5, causing me to push out and tag a cone in the wall. The ARB (anti-roll bar) is made by Hellwig. They are sending me a replacement bar for free under warranty. I have had both the front and rear bar for about 7-1/2 years.

If this hypothesis is correct, I believe it would support the argument that the car needs the rear stiffness it has (or maybe more) since losing the rear bar would impart more weight transfer on the front and thus reduce the front end's tractive capacity.

What do our fine pro-touring.com members think?

Thanks again to all who have contributed to this discussion.

[Sleeper68]

The broken sway bar has been fixed and some other issues have come up. Two events have been completed so far this year with not the best results. Setups below:

SETUP 7: Post-spindle failure. -2.25° Camber, +6.75° Castor, 0" total toe.

SETUP 7.5: Broken/cracked rear sway bar. -2.25° Camber?, +6.75° Castor?, 0" total toe?.

SETUP 8: Replace broken rear sway bar. -1.5° Camber, +6.50° Castor, 0" total toe. This setup snuck up on me. The the change in camber happened gradually overtime and seemed to result from loose upper ball joints. This prompted an evaluation of all Howe adjustable rod ends and ball joint on the car. I found that all four (both upper ball joints and both outer tie rod ends) were slightly loose to the point of lash. This was addressed and corrected in SETUP 9. It is unclear how long they ball joints had been loose. The car pushed at 2023 Event #1 with this setup and was difficult to place on the racing line. Tires were fairly cold at that even due to semi-wet and dusty course, low ambient temps, and low solar angle.

SETUP 9: -2.5° Camber, +6.8° Castor, 0" total toe. A different toe measurement method was used (toe bars on camber caster gauge, straight edge on opposite wheel, tape measure). This method is far easier to prepare but I fear it is far less accurate. Previous toe measurement and adjustment had been facilitated with a set of parallel strings attached to jack stands that had been aligned to the center longitudinal axis of the car. Toe was measured by taking the difference between front and rear distances to the wheel lip from the string on each side using a machinist scale. I am switching back to the old method but I am going to streamline it by making two tubes with notches at equal distances to locate the string eyes.

Event #1: Car pushed, my driving was sloppy, tires were cold, track was wet in places and very dirty/graveled. I had it in me to win but I hit a cone in a wet section on my fastest raw run.

https://youtu.be/370CngHJhpY

Event #2: Loose ball joints fixed, camber changed to -2.5°, car was far looser than before. The surface was cold, I was sloppy and not used to this setup, and mine lines were wide in places which killed me on a slow course like this one. I think there is room to improve the car's balance with with a rear shock or rear sway bar adjustment. Toe could be compromised and not actually 0". Need to re-check with the original, validated toe measurement method.

https://youtu.be/pOWlzmbBzkc