[Ron Sutton]

Rob,
And anyone reading along with us …

The following helps explain each suspension set-up or tuning item in more detail.

The “Soft Front Spring/Big Sway Bar - High Travel/Low Roll” set-up loads the front tires more on corner entry & braking … and therefore unloads the rear tires more … than “Conventional Stiff Front Spring/Small Sway Bar – Low Travel/High Roll” set-ups.

An additional benefit of the front end compressing more & is it acts like stored energy on exit … allowing more front end lift travel under throttle, for increased load & grip on the rear tires.

Utilizing this strategy for this application is based on the need to:
a. Assist this long 116" wheelbase car to turn better.
b. Overcome a 21% larger rear tire bias.

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Here are the keys to this modern suspension strategy & a few other tuning suggestions, all designed to take a car that would otherwise push … due to the long WB & 21% bigger rear tires … into a good turning road course track car.

1. The KPI/Caster Split favoring the caster … combined with a small amount of caster gain in dive … corrects the angle of both inside & outside wheels … to achieve a full contact patch with both front tires for optimum cornering ability … without running excessive static camber.

2. The “anti-dive” built into the A-arms helps prevent the soft front suspension from compressing too fast under braking. Plus provides the desired caster gain.

3. Achieving camber gain with the A-arm/spindle/ball joint geometry means we don’t need as much static camber. You want some static camber, as it loads the outside front tire instantly on turn-in … improving responsiveness. Just don’t get greedy, and run more camber & less caster. Caster helps both tires achieve the correct tire contact patch… and is progressive. Camber helps the outside tire angle & hurts the inside tire angle & is always doing it. I see some AutoX guys with 5-6 degrees of camber and during corners the inside front tire is using half the contact patch or less.

4. You want a little toe-out. Like static camber, static toe-out improves initial turn in responsiveness.

5. Get the rest of the “dynamic toe out” with Ackerman or bump steer. In race cars, it almost doesn’t matter which we use, because the suspension is always compressed in the corner when we’re turning. Ackerman is the preferred method in a PT car, so you get the benefit on the street too, when the suspension is not compressed. Regardless, you need the inside front tire turning at a tighter radius than the outside tire for optimum front tire grip. Otherwise, you’re dragging the inside tire, instead of the inside tire helping the car to turn.

6. The softer front springs allow the front end to travel farther on corner entry & braking. This varies by application, but the goal is 2”+ instead of ¾”-1” of a conventional set-up. This loads the front tires more, giving them more grip & providing better turning ability.

7. The huge front ARB, plus stiffer rear springs & stiffer than most rear ARB … all work together to keep the car at a low roll angle. This keeps the inside front tire engaged more than a high roll set-up. It also unloads the rear tires more evenly.

8. The stiffer, stronger (and shorter if possible) ARB Arms … load the tires quicker … and make the car more responsive. You will need this in a big, wide, 116” wb car.

9. The front roll center at 1.25"-1.5" “in dive” seems low, but is actually a little high … which is best for loading the front tires on road courses. If you were AutoXing, we would run it around 0” in dive.

10. The rear panhard bar at 11” is high … only to free up the load & grip on the 345 rear tires … and to help the suspension keep the inside front tire loaded during cornering. This will be one of the first things you should tune on at the road course track. If the car is loose, you will lower it. If yours is not infinitely tunable … correct this. Having a non-adjustable panhard bar in a handling car is ridiculous.

11. The 4-link specs I provided will provide more traction on exit and frankly assist with weight transfer from the rear tires to front tires on corner entry. This needs to be tuned to find the happy balance. If you increase the downward angle of the top link, you will add “initial” grip to the rear tires on corner exit as you pick up the throttle … AND it will transfer more weight from the rear end to the front end, as the rear lifts under braking. If you go too far … in search of exit grip … you will make the car loose on entry.

12. The lower bars of the 4-link (3-links too) control “rear steer” or “roll steer”. If you run the bars level at ride height … or 0.0 degrees … as the car rolls over in a corner … both bars pull the rear end forward the same amount, so the rear end stays “true” to the chassis. If you raise the front of the bars (at the chassis mount) or lower the rear (at the rear end housing) you get rear steer … meaning the outside tire is pushed back & the inside tire is pulled forward. This helps steer the car from the rear a little like the fork lift concept.

More angle is more rear steer. Going down in the front or up in the rear, acts in the opposite way, pushing the outside tire forward & the inside tire is pushed back, which does the opposite, causing the car to “tighten” as it is being steering to the outside of the corner. Rear steer affects the exit too, because the car is still rolled over to a degree. So I use rear steer as a tuning tool to free up the car when it is tight or pushy mid-corner & exit.

13. Again, I’m not willing to share my proprietary valving info on a Forum, but you need front shocks valved to have the front end compress at a nice, controlled, smooth rate … and keep the front end down through the middle of the corner, after you have lifted off the brakes … and release & let the front lift as you roll on the throttle.

14. Having front wheels wider than the tread width will improve both initial turn-in responsiveness & front tire grip. Having the rear wheels equal to the tread width will help free up the car on entry & middle & help grip up the car on exit.

Make sense? Got questions?
Everyone feel free to chime in if you have relevant conversation.

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