GT350 vs. Z/28

[thePill]

That's what I got out of it. I see it making a marginal difference at best.

Bud, in my business, marginal is everything. We split hairs and then split them again. Serious vs. Casual... I am looking for marginal gains and losses, some costing thousands of dollars.

If you guys are just casual drivers, just disregard everything and drive.

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[Stuntman]

Pill: Are you saying you can change Front to rear weight distribution by changing tire pressure? How about spring rates?

 

[thePill]

Increasing the tire pressure in say, the right rear increases both the weight registered on that corner as well as increase the weight on the opposing corner. NO, we didn't add any weight at all...

Anyone know why?

Stuntman, no spring change, just tire pressure. No weight added, just an increase in weight AND X distribution %. It happens here everyday...

 

[thePill]

I think we are done here... This is Chassis 101, Day 1...

Look into some Technical Schools, be sure there is a Motorsport Chassis Program available after your core.

This is not a good place to learn, even from a Chassis Fab Engineer.

 

[Stuntman]

Yes it's simple, but if you think reclining a seat lowers the RC (which it doesn't), I wanted to see if you knew the answer to the above question due to your vague statement a few posts ago.

 

[Norm Peterson]

Increasing the tire pressure in say, the right rear increases both the weight registered on that corner as well as increase the weight on the opposing corner. NO, we didn't add any weight at all...

Anyone know why?

For cornerweighting purposes, a tire is just another spring in series with the suspension, suspension component flexibilities/compliances, pickup point brackets, etc.


Norm

 

[Trackaholic]

I think we are done here... This is Chassis 101, Day 1...

Look into some Technical Schools, be sure there is a Motorsport Chassis Program available after your core.

This is not a good place to learn, even from a Chassis Fab Engineer.

Hmmm....

-T

 

[w3rkn]

Yes it's simple, but if you think reclining a seat lowers the RC (which it doesn't), I wanted to see if you knew the answer to the above question due to your vague statement a few posts ago.

define RC..

Think about the axis

 

[thePill]

define RC..

Think about the axis

I believe he was thinking lowering the static RC as the vehicle rest. I added in the "RC" at the end of "lower the CG" and he jumped on it like a roach.

We would try to avoid geometry changes if we could keep the RC stable. On a 5th Gen however, that is a challenge...

Initially, I thought the dramatic changes on entry and mid corner were due to poor front geometry coupled with an insane front tire size. However, sometime in 2012, we found out that the rear suspension's RC could possibly be diving below the datum on some corners. This was partially remedied by shifting some equipment around or, as we call it, corner balancing. Some very small changes evened out that possible event and this random and sudden severe oversteer was helped by limiting weight transfer and keeping the IRS from massive deflection under heavy lateral load.

I think Cheveventualy (LOL at the auto correct!!!!) changed the rear suspension all together in 2012/13. Although, I was informed that those changes were basically band aids for the system. It added weight and literally kept very similar geometry.

What do I know... I'm just breathin' air over here...

 

[Stuntman]

define RC..

Think about the axis

Roll Center (Kinematically): The point in the transverse vertical plane through any pair of wheel centers and equidistant from them, at which lateral forces may be applied to the sprung mass without producing an angular (roll) displacment o the sprung mass. -Dave Segal

...Found by projecting a line from the center of the tire -ground contact patch through the front view instant center...where these two lines (for each side of the car) intersects is the roll center - Terry Satchell.

 

[thePill]

Roll Center (Kinematically): The point in the transverse vertical plane through any pair of wheel centers and equidistant from them, at which lateral forces may be applied to the sprung mass without producing an angular (roll) displacment o the sprung mass. -Dave Segal

...Found by projecting a line from the center of the tire -ground contact patch through the front view instant center...where these two lines (for each side of the car) intersects is the roll center - Terry Satchell.

Terry Satchell is a moron... The Roll Center is where the IC intersects the Chassis Centerline. Dave is making it more complicated than it really is...

Stop using Google...

For reference, that "line" that extends from the IC is called "Swing arm". The distance from your CG to your Swing Arm is a Moment Arm. Keep the moment arm short when designing suspension. The Outside Scrub Radius (Not the "ground contact patch") is where the swing arm extends to from the Instant Center.

Uggggg!!!!!

 

[Stuntman]

Terry Satchell is a moron... The Roll Center is where the IC intersects the Chassis Centerline. Dave is making it more complicated than it really is...

Stop using Google...

No it's not.

Fist off, the instant center is a point in space and usually never occupies the centerline of the car. You determine the roll center by the above quote, by projecting a line from the tire contact patch to the instant canter. Where these two lines (from each contact patch to corresponding instant center) intersect is your roll center. It's easier to just do one side of the car and usually the RC is right on the centerline, but not always.

Heck, you even (surprisingly) said, that the RC migrates. It migrates vertically as well as laterally. Your 'centerline' of the car statement does not account for the RC location in roll -which is why it's more accurate to look at where the two stated lines intersect to determine the RC location for both static and dynamic RC location.

I'll finish the quote: "...It is not necessarily at the centerline of the car, especially with asymmetric suspension geometry".

Do you even know who Terry Satchell is?

Oh, and the quote is not from Google. It's from a book that you would own if you are truly had any clue...

For reference, that "line" that extends from the IC is called "Swing arm". The distance from your CG to your Swing Arm is a Moment Arm. Keep the moment arm short when designing suspension. The Outside Scrub Radius (Not the "ground contact patch") is where the swing arm extends to from the Instant Center.

Uggggg!!!!!

You're reading comprehension (and general understanding) still remains extremely poor.

You are often limited by many factors that determine your CG height. If you simply made the moment arm short by raising the RC, you'll have a lot of adverse effects and jacking of the car. You can't make make the generalization to 'keep the moment arm short'.

 

[thePill]

He didn't even know the name of the "line", and your quoting this guy. I don't care who he is...

Your Swing arm length intersects:

Your Chassis centerline
Your Control Arm Attachment line
And your SAI.

IC isn't imaginary...

It consist of your swing arm, lower control arm line, upper control arm line and tie or toe line.

I'm not sure I understand his statement at all... Even a proper swing arm length will intersect the chassis centerline, ie, meet in the middle. I think your just making that up.. If it doesn't, your suspension geometry isn't the same on each side. Or your running two different tires with unique scrub radius's for oval.

I am willing to hear an explanation though,...

Are you sure your chassis is centered between your wheels? LOL!!!

 

[thePill]

Bring your car to me, we'll TRY and straighten you out for this season. Pay special attention to what Dave says. "Center between two wheels"... and how do we get our Chassis Centerline to begin with?

 

[Stuntman]

He didn't even know the name of the "line", and your quoting this guy. I don't care who he is...

Your Swing arm length intersects:

Your Chassis centerline
Your Control Arm Attachment line
And your SAI.

IC isn't imaginary...

It consist of your swing arm, lower control arm line, upper control arm line and tie or toe line.

I'm not sure I understand his statement at all... Even a proper swing arm length will intersect the chassis centerline, ie, meet in the middle. I think your just making that up.. If it doesn't, your suspension geometry isn't the same on each side. Or your running two different tires with unique scrub radius's for oval.

I am willing to hear an explanation though,...

He's a heck of a lot smarter than either of us. If you took any form of motorsport engineering classes, you probably would have read some of his work.

The plane of your upper and lower arms intersect at a point. This is your instant center. A line is drawn from the contact patch to the instant center for each side of the car. Where these two lines intersect is your roll center.

We are not talking about the rolling moment of the CG around the RC.

Again, while you could just assume the RC is where this line intersects the car's centerline, you need to look at both sides of the car especially when the car rolls to determine the RC location as it migrates vertically and laterally. If you don't understand this, you really need to take a few steps back and learn what you're talking about.

You seem to know enough to be dangerous but not enough to really know what you're talking about.

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