Total Lateral Load Transfer Distribution

[Sleeper68]

This post is provide an update as to how the car and myself have been performing since the last post.

List of events since last post:

HSSC 03 OCT 2021, BFG Rival S 1.5, Setup 5: https://youtu.be/L6FEjmYwQUY Very cold. Tires were about out of life here.

TRSCCA OctoberFAST Day 1 31 OCT 2021, Wet, RT660, Setup 6: https://youtu.be/Iv36rB08GYQ Falkens worked great. Alot of turn-in understeer but it was wet.

TRSCCA OctoberFAST Day 2 01 NOV 2021, Dry, RT660, Setup 6: https://youtu.be/H83PK4gJ9JI Love how fast the RT660s heat up. Great for a one driver car.

ETRSCCA Points #1 06 MAR 2022 BRISTOL, Setup 7: https://youtu.be/P1UkFrvwsqs First event post-spindle failure. First time and bristol (high speed courses) with the new tires.

ETRSCCA POINTS #2 03 APR 2022 SMOKIES STADIUM: https://youtu.be/ahyv41IntUs Starting to learn how the car drives with the new Falkens. They are more precise and provide far more feedback than the BFGs.

ETRSCCA POINTS #3 15 MAY 2022 BRISTOL: https://youtu.be/h5ZU228ThRs

ETRSCCA POINTS #4 29 MAY 2022 SMOKIES STADIUM: https://youtu.be/G0QG2SxoYRw

ETRSCCA POINTS #5 12 JUN 2022 BRISTOL: https://youtu.be/zXOY9T7Akzc The falkens can certainly get greasy when it is super hot outside, especially in the rear when applying power at the end of the run. Setup 7 is definitely working the outside rear tire more than before based on temps. Could also be driving improvement.

ETRSCCA POINTS #6 10 JUL 2022 SMOKIES STADIUM: https://youtu.be/gWhB4XF6apg

ETRSCCA POINTS #8B 24 JUL 2022 BRISTOL: https://youtu.be/ERG2jg3YfOk

ETRSCCA POINTS #9 21 AUG 2022 BRISTOL: https://youtu.be/gnW6uy7s5L8

ETRSCCA POINTS #10 09 OCT BRISTOL: https://youtu.be/sAUohwkN96A

As you can see from these videos, the car understeers far less and generally rotates better; however, it still understeers in steady state cornering. I think the balance (TLLTD) is still off, but I think there is another contributing factor. More on that later.

Thanks to contributions from members here at pro-touring.com and some driver improvements, I have been able to win the 2021 and 2022 ETRSCCA points championship for CAMT. I want to take this opportunity to thank everyone who has contributed to this thread. Public discourse, in my opinion, is very good for improving all of our understanding of vehicle dynamics.

My next area of focus for the car is fixing the steering geometry and the excessive steering arm flex the car has. The steering arms are made by Chassisworks of 7075-T73 Aluminum https://www.cachassisworks.com/p-295...-aluminum.aspx. The fact the steering arm is aluminum and because of the very low position of the outer tie rod end (approx 0.2" from the wheel inner lip), the steering arm flexes. This excessive flex (approx 0.2" of movement of the outer tie rod before the wheel moves when car is static on the ground) makes the car very hard to place while racing on the limit.

So, my plan currently is to use a higher inner tie rod pivot to allow the outer tie rod to move up. Currently, I want to use the ridetech TruTurn centerlink/draglink instead of modifying a factory one or making my own. This will reduce the cantilever distance to the outer tie rod from the spindle. Additionally, I will need new steering arms to accommodate this so I will be making my own steering arms from steel with very similar Ackermann geometry to the Chassisworks units. The combination of the fact that steel is stiffer than the aluminum and the reduced cantilever should make for a much stiffer steering system.

Now, back to why I think the car is understeering in steady state: It could be the balance is still biased to understeer due to weight transfer, and shock settings are improving turn-in and transient balance; hiding the steady state balance issue. There could be another issue though, one related to the known steering arm flex. It COULD be that once the car is cornering hard and virtually steady, the steering arms (especially the outside steering arm) are flexing so much that the dynamic toe has changed to be very toe-ed in. Maybe this is part of the steady state understeer issue? Maybe I should return the inner upper control arm pivot point to the OEM holes and maintain the 0.5" tall or 0.9" tall UBJ?

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

I think we all will agree that the steering arm flex should be reduced as much as possible.



The suspension tuning progression:

SETUP 1: The first significant front RC change I did was achieved by going to a 0.9" tall upper ball joint from a factory one on otherwise stock geometry (raised roll center ~ 1.25" and made camber gain negative instead of positive - 0.3°/in). This was in 2015. -3.0° camber , +6.0° castor , 0.0" toe

SETUP 2: The second front RC change was done in 2020 by lowering the inner pivot of the upper control arm about 1/2" rear hole 5/8" front hole (raised front roll center ~1.1" and made camber gain more aggressive 0.8°/in). This also had the effect of reducing front anti-dive since it is fairly excessive in first gen camaros. The reason for the second change was because I found I had to run alot of front camber (2.7°-3.0° neg) to keep the front tires happy but this came at the cost of poor front end grip in braking. I attributed this poor braking performance to the excessive static camber after playing with brake pressure proportion (ended up with full bias to rear tires in braking, still locked up front tires with even small amounts of trail brake). The idea was to increase camber gain and thus reduce the need for static camber. The inadvertent effect was a stiffer front end due to the higher front roll center. -1.5° camber , +6.5° castor , 0.0" toe.

SETUP 2.5: Rear RC moved up to 13.5" from 12.5". Rear ARB endlinks changed to rod end style from polyurethane-bushed style. -2.0° camber , +6.5° castor , 1/8" total toe out



SETUP 3: The third front RC change was performed in 2021 by going to a 0.5" tall upper ball joint from 0.9" tall (lowered front roll center ~0.5" and made camber gain less aggressive - 0.6°/in). This change was made in an attempt to "split the difference" between change one and two. -2.1° camber , +6.7° castor , 1/8" total toe out.

SETUP 4: Change to softer front jounce bumpers. Increased front damper bump travel (reduced rebound travel) by moving the lower damper mount down in relation to the lower control arm. -2.1° camber , +6.7° castor , 1/8" total toe out

SETUP 5: Front eyelet bushing of leaf springs changed to aluminum/delrin/steel bushing with thrust washers from steel/rubber/steel bushing. This eliminated any appreciable compliance in the bushing and forced the rear leaf springs to comply with roll, effectively increasing the rear roll rate. -2.1° camber , +6.7° castor , 1/8" total toe out.

SETUP 6: Switched from BFG Rival S 1.5 to Falken RT660 tires (same size 275/35R18). Reduced toe out to zero. -2.1° camber , +6.7° castor , 0" total toe out. This change occurred just before an event at NCM Racetrack in Bowling Green, KY in OCT of 2021.

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