1969 Torino

[FETorino]

Originally Posted by DOOM

Rob I like all the progress you've been making with this beast! Keep it up!

Thanks Mario. I hear there are bowties that will be prowling the streets with Twin Turbo Big Blocks in them so I need to be prepared.

Originally Posted by Ron Sutton

If your car is already “designed & built” … and the track width is a wider in the front, that will “contribute” to the car being tight/pushy a degree. If the track width is a narrower in the front, that will “contribute” to the car being free/loose to a degree. I use the word contribute, because there are a lot of other suspension & geometry factors affecting the grip at each end of the car. If the track width is not adjustable at either end, you will need to tune with roll center, springs & sway bars to balance the car.

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Uh Yea? How about that?

[Ron Sutton]

Originally Posted by FETorino

Uh Yea? How about that?

I'm not sure what you said, let alone how to respond.

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[FETorino]

Originally Posted by FETorino

Uh Yea? How about that?

Originally Posted by Ron Sutton

I'm not sure what you said, let alone how to respond.

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Hmm I know of a car as you described above It sounds familiar.

Oh yea that would be mine

Pretty much non adjustable track width without a involved.
Track in front a little narrower than the rear. Although I have tightened that up a bit by and looking at .

there has been a fair amount of discussion on the spring, shock and bar package for my set up.

So it seems that leaves us @

Tune with roll center. Yep that's it

[Ron Sutton]

Rob,

I get it now.

Yes ... your car's wider rear track width ... by 2" ... helps us free up the rear of the big girl a bit. This is a step in the right direction to help overcome the bigger rear tires, but by itself wouldn't be enough.

In the suspension set-up I outlined for you, I bumped the rear spring rate & sway bar rate a "tad" ... but raised the rear panhard bar (roll center) more ... also to help free her up.

Once you hit the track, we'll need to "tune on her" to achieve a good balance & optimum set-up.

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[Ron Sutton]

Alrighty then ... let's talk Roll Centers.

I’ll be very basic for any readers following along that are completely new to this & apologize in advance for boring the veterans with more knowledge of this. Cars have two roll centers … one as part of the front suspension & one as part of the rear suspension. I’ll first explain what role they play in the handling of a car … then how to calculate them … and finally how to tune with them.

Think of the front & rear roll centers as pivot points. When the car experiences body roll during cornering … everything above that pivot point rotates towards the outside of the corner … and everything below the pivot point rotates the opposite direction, towards the inside of the corner. Because the front & rear roll centers are often at different heights, the car rolls on different pivot points front & rear … “typically” higher in the rear & lower in the front.

If you were to draw a line parallel down the middle of the car connecting the two roll centers … this is called the "roll axis" … that line would represent the pivot angle the car rolls on … again “typically” higher in the rear & lower in the front.


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[Ron Sutton]

When a car is cornering … the forces that act on the car to make it roll … act upon the car’s Center of Gravity (CG). With typical production cars & “most” race cars, the CG is above the roll center … acting like a lever. The distance between the height of the CG & the height of each Roll Center is called the “Moment Arm.” Think of it a lever. The farther apart the CG & roll center are … the more leverage the CG has over the roll center to make the car roll. Excessive chassis roll angle is your enemy, because it is over working the outside tires & under utilizing the inside tires.

Some people like to look at the car as a unit. I look at it as two halves. Here are some examples … using a typical 3500# Pro Touring Car with 53% front weight… to provide more clarity:

If the CG is 20” high … and the front roll center is 2” below ground … the car has 53% of the 3500# weight with 22” of leverage to roll the front of the car.
If the CG is 20” high … and the rear roll center is 9” above ground … the car has 47% of the 3500# weight with 11” of leverage to roll the front of the car.
* Rolling the car that much more in the front overloads the outside front tire & under utilizes the inside front tire when cornering.

If you lowered the car 2” … the CG drops 2”. The front roll center probably moved too … but it’s not linear … it is based on A-arm angles. Let’s say it dropped 1” in the front to 3” below ground and the rear stayed the same at 9”.

Now …
If the CG is 18” high … and the front roll center is 3” below ground … the car has 53% of the 3500# weight with 21” of leverage to roll the front of the car.
If the CG is 18” high … and the rear roll center is 9” above ground … the car has 47% of the 3500# weight with 9” of leverage to roll the front of the car.
* The front now rolls over less & the rear too, making the car run “flatter” … not flat, just less roll angle … working the inside tires better.

Any weight you can remove from high up … or relocate to lower in the car … moves the CG down … reducing the leverage it has over the roll center … allowing the car to have less roll angle during cornering … working all four tires more evenly … and the grip of four tires is faster than two.

We’ll discuss moving the roll centers in the final section. Next, let’s cover how to figure out where your front & rear roll centers are at.

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Front: Measuring all the pivot points in the front suspension to calculate the roll center in the front suspension of a double A-arm suspension car can be tedious … but the concept is quite simple.

Quick Acronyms:
UCA = Upper Control Arm
LCA = Lower Control Arm
BJC = Ball Joint Center
IC = Instant Center
RC = Roll Center
CG = Center of Gravity
CL = Centerline

Your UCA & LCA have pivot points on the chassis … and they pivot on the spindle at the BJC’s. Forget the shape of the control arms … the pivots are all that matter.

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[Ron Sutton]

If you draw a line through the CL of the UCA pivots & another line though the CL of the LCA pivots … they will intersect at some point (as long as they are not parallel). That point is called the instant Center (IC) … and the UCA/Spindle/LCA assembly travels in an arc from that IC point. However far out that IC is … measured in inches … is called the Swing Arm length. More on this later.

Next you draw a line from the CL of the tire contact patch at ground level … to the IC. Do this on both sides … and where the two “Tire CL-to-IC” lines intersect … is the front roll center. Look at the drawing below. The colored dots represent the IC for the same color LCA/UCA. The black dot represents the static RC at ride height.

Make sense?

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[FETorino]

I just catching up on some light reading before I dove into Ron's posts.

[Ron Sutton]

That is cool Rob.

Love the old stuff.


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[fleet]

Originally Posted by Ron Sutton

That is cool Rob.

Love the old stuff.


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X2.

Now how about posting some of your vintage '68 Camaro pics?