1969 Torino

[Ron Sutton]

Rob,

I tell most everyone, "we can go no faster through the corner than the front end has grip" ... and since we have 285's on the front of a big car ... we need to optimize them to their fullest potential, within the limitations you have put on the car yourself: no fender mods, 2" of front wheel lip, etc.

Here are the keys:

1. Your KPI/Caster Split should favor the caster by 0.5 to 0.75 degrees. Your C6 spindles have 9.15 degrees of KPI. Which would mean you want 9.65 to 10 degrees of static caster. That "seems like" a lot of caster, but just what the doctor ordered. GM runs this spindle at 7.7-8.3 degrees of caster in the stock Z51 & all the fast Corvette track guys run 10.0-10.5 degrees of caster.

2. You will want the A-arms installed to achieve "anti-dive." That means the LCA angles down in front & the UCA angles up in front. This will compliment the suspension set-up I'm going to recommend. And it will provide you with dynamic "caster gain" as the suspension compresses. You need about 0.5 degrees of caster gain. If you end up with more ... which would be good ... you need to reduce your static caster by the amount above 0.5 degrees.

3. How much camber gain you can end up with will also affect your roll center. Since your priorities are road course track days, Silver State high speed runs & Optima type "all around" performance events, you'll want a slightly higher front RC than you would for AutoX. I'd say 4" at ride height & 1.25"-1.5" in dive. That is easy to get by increasing the UCA angle (taller spindle or ball joint) ... which will also increase camber gain.

4. If you end up with 2.0 degrees of camber gain, I'd suggest a "starting point" of .75 degrees of static camber, for a total of 2.75 degrees of camber in dive (suspension compressed). If you end up with less camber gain ... add more static camber ... and keep the 2.75 degrees total. Other tuners may tell you need way more camber, but they're not used to working with a KPI/Caster Split favoring the caster.

5. Run .060" total toe-out. Yes ... out. Then play with the Ackerman & bump steer ... so you end up with .140"-.150" toe out ... in dive ... with the wheels turned 20 degrees.

6. You need to transfer a high amount of weight off the rear tires & onto the front tires for optimum cornering.

7. You need to achieve & maintain a low roll angle to optimize the front tire contact patches.

8. Therefore the optimum suspension set-up for your ride would be a high travel front end ... to achieve high pitch change & low roll angle ... also known as soft spring big bar.

I'll hop back on here tomorrow & outline the suspension set-up to achieve this ... along with tuning tools to balance the car at the track.

[Ron Sutton]

I corrected post #1212 after getting a PM from Rob with his spindle info.

I did not correct earlier posts to reflect his correct track width difference of 2" wider in the rear, but we'll use that number from here on out.

[Ron Sutton]

Hey Rob,

I've calculated the wheel spring rate we need, but to tell you what spring rates to get, I'll need "True Spring Motion Ratios" that include spring angle from your chassis builder ... so get front & rear ... and post them.

We may be able to work with your existing rear sway bar, if the effective rate is high enough. Typically AME's have 3 positions. Get the effective rate in all 3 positions & post.

Might as well get & post the effective rates for the front sway bar too, but I doubt it will be high enough for the SS/BB set-up I'm going to recommend.

[Ron Sutton]

Rob,

What I have outlined below is a soft spring/big bar … high travel, low roll suspension setup that you & I discussed … to optimize the handling of your long wheelbase car with tires 21% larger in the rear.

It is just a baseline to start from ... and it assumes a lot of things for us to discuss & get clear on. Most of these assumptions can be tuned around, if my assumption is wrong. Some can not.

Assumptions:
3500# car
116" Wheelbase
51.5% front weight
19” CG height
2.5”-3” front shock travel in dive
Front track width 56” & rear 58” / 2” wider in rear
285 front tires & 345 rear tires / Same compound front & rear

Readers … do not run with this set-up for your car. That would be like taking someone else’s medicine when you have no idea what health issues they have. I can not say this strongly enough. This is not a universal set-up or even a universal concept. I have outlined this for Rob’s long wheelbase Torino with tires 21% larger in the rear & a 2” wider rear track width.

Baseline Starting Point to Tune From:

Springs & ARB's:
Front Wheel Rate: 275#
Front Spring Motion Ratio: _________?
Front Spring Rate: _________?
Front ARB Effective Rate: 1050#
Rear Wheel Rate: 350#
Rear Spring Motion Ratio: _________?
Rear Spring Rate: _________?
Rear ARB Effective Rate: 400#

ARB (Anti Roll Bar) Arms:
Front: Short, strong (4130 chromoly)
Rear: Steel, no aluminum

Front Roll Center: 4" at ride height & 1.25"-1.5" in dive
Rear Roll Center: 11” with level Panhard Bar at ride height

4-link Specs:
Lower Bars: 0.0 degrees / Level at ride height
Upper Bars: 9-10 degrees down in front
Instant Center: Same height as lower bars … 50-60” ahead of rear axle CL
Pinion angle: 2-3 degrees negative from the driveshaft*

Front Shocks:
I’m not willing to share my proprietary valving info on a Forum. In general, you will need moderate compression valving in the front, to slow the rate of compression on braking & corner entry & substantial rebound valving to hold the front end down through the corner.

Rear Shocks:
Again, I’m not willing to share my proprietary valving info on a Forum. In general, you will need moderate compression valving in the rear, to slow the rate of compression on & corner entry & moderate rebound valving to keep the rear tires planted on corner exit.

Adjustable Shocks:
Triple adjustable shocks ... low-speed rebound, hi-speed rebound & hi-speed compression ... are a key to dialing in a bad ass race car on track day ... and dialing it back to a drivable Pro Touring car at the end of the day. There are poor shocks, good shocks & great shocks available. I choose not to talk brands on a forum.

Wheel width:
Your 285’s need to be on wheels 1” wider than the tread width & put the rear tires on wheels with the same width at the tread width. You want the front tires “stable” and you want the rear tires to “move around” a little.

Tire pressures:
Optimized for full contact patch & even temps.

Rob, as with all cars that get pushed to their limits ... when you find the limits, you WILL NEED TO TUNE on this set-up. I’ve got you close … except for shock valving … which we’ll need to discuss.

In my next post, I’ll outline some tuning strategies after you run it on a road course. And if you want, we can discuss some changes for better AutoX performance.

[FETorino]

Originally Posted by Ron Sutton

Hey Rob,

I've calculated the wheel spring rate we need, but to tell you what spring rates to get, I'll need "True Spring Motion Ratios" that include spring angle from your chassis builder ... so get front & rear ... and post them.

We may be able to work with your existing rear sway bar, if the effective rate is high enough. Typically AME's have 3 positions. Get the effective rate in all 3 positions & post.

Might as well get & post the effective rates for the front sway bar too, but I doubt it will be high enough for the SS/BB set-up I'm going to recommend.

Hey Ron. I just got home from running errands and goofing around at a buddys house. I'll take some measurements tomorrow and get some specs.

I went down to Speedway Engineering today to grab the proper drive plates, inner seals and dust caps.

I continue to be impressed with the Machine work done by Travis and crew at Formula 43. The drive hubs in the last pic are being held in place by the perfect interference fit of the hub to the wheel center. Hub centric magic at its best Travis.

[intocarss]

Real technical advice, clear pictures of high $$$ race parts...... WHAT THE HELL IS GOING ON IN HERE??

[Rick D]

Man Rob your thread is just dripping with tech now, this is great!! It kinda drowns out all the BS although I'm sure once you slow down on the tech and progress it will be full steam ahead!!

[Ron in SoCal]

Fun little road trip yesterday. Rob and I stopped at Speedway and we're like two kids in a candy store. Their finished parts warehouse was just so cool. Snouts, drive plates, dust covers, housings, crowned axles you name it.

I couldn't help but pick up and admire at least one of everything and you can see above the quality of finished products. And the people there are just great too.

I think Rob bought an extra drive plate to be made into a hip hop/car guy necklace

Dust cover and fit looks killer Rob.

[Ripped]

Wow, you are sure not cutting corners anywhere! I don't know how you sleep much at night, as all of this all comes together.

What is your projected completion date?

[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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