GT350 vs. Z/28

[thePill]

Anyway, Norm is correct and I'm sure he knows what that commonly overlooked "spring" does to the other corners. You can make a lot of money just by airing the tires and scaling.

Now, back to our 4200lbs race weight, left front biased 2014 z28.

Since we are at 4250 w/ driver, 6 point cage and safety equipment, our WD would be close to 50/50. Keeping the seat and safety equipment on the right side will help balance out this 4200lbs ride. We are kinda screwed on weight reduction upstairs but, unsprung weight will come down from here. Wheels, tires, brakes... all are gone... A driver seat is coming out for sure. I'm thinking there might be 100lbs in wheels and brakes to be saved... We would need to retune the LS7 a bit and recert.

IF, and that's a big IF... If we can increase caster some, it may help the Mac P strut with camber change in the corner. It will limit our static camber BUT, I feel an increase in caster could help with camber gain... an area Mac P systems fall behind in. The Mustang doesn't suffer as much with this for countless reasons, mostly due to rear suspension geometry and the live axles torque steer... In short, it rotates the car whether the Mac P system likes it or not. The 5th gen's rear can be unpredictable which is why I feel the RC is diving below the datum on some corners. It really depends on the corner...

I'm sure what's his face is really smart... and like him, I sometimes forget the names of vital nomenclature when writing my books... Unless he's talking down to you in his book in which I can relate even further...

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[Stuntman]

Which books have you written exactly?

I personally don't feel that 50/50 is "ideal" by any means, especially if you can move weight around or change tire widths. However for most FR cars, 50/50 is already a challenge.

I don't see how increasing caster would be a problem in the camaro.

 

[thePill]

Caster increases are a pain in the ass on Mac P systems...

Edit: ^ Name of the book I wrote.

Edit2: moving weight around would eventually achieve a near (and apparently not ideal) 50/50/50/50 WD. Unless your moving weight to avoid 50/50/50/50 which is practiced at the oval.

Changing tire widths will lower your roll center, yes, actually lower the static point permanently. This is because the swing arm length angle to the instant center has been lowered by pushing your outside scrub (outer most point of your contact patch) further out. Along with a nice neutral balance and lower CG, it should handle well. However, watch your RC's movement during deflection, if it dives below the datum, you'll have a 4200lbs, $80,000 accident.

 

[Norm Peterson]

I personally don't feel that 50/50 is "ideal" by any means, especially if you can move weight around or change tire widths. However for most FR cars, 50/50 is already a challenge.

That 50/50 might be ideal has to be a carry-over from the early 1960's with the further stipulation of equal front and rear tire size.

I don't see how increasing caster would be a problem in the camaro.

Bumpsteer.


I rather think a force-based analysis using actual wheel loadings would be more useful than a purely kinematic model, since once the car has rolled, the forces along the FVSA's are no longer identical, nor are the inboard and outboard suspension geometric resistances to roll equal.


Norm

 

[Stuntman]

Caster increases are a pain in the ass on Mac P systems...

Edit: ^ Name of the book I wrote.

Edit2: moving weight around would eventually achieve a near (and apparently not ideal) 50/50/50/50 WD. Unless your moving weight to avoid 50/50/50/50 which is practiced at the oval.

Changing tire widths will lower your roll center, yes, actually lower the static point permanently. This is because the swing arm length angle to the instant center has been lowered by pushing your outside scrub (outer most point of your contact patch) further out. Along with a nice neutral balance and lower CG, it should handle well. However, watch your RC's movement during deflection, if it dives below the datum, you'll have a 4200lbs, $80,000 accident.

Where could I find it? I'd love to read it.

Widening the tire but keeping the centerline of the tire the same shouldn't have an affect on the RC, however widening the track width with a lower offset wheel will slightly increase the height of the RC.

Bumpsteer.


Norm

And how does that differ from any other MacP car?

 

[thePill]

Remember, your Swing Arm Length is measured from the Instant Center to the Outside Scrub Radius, not the tire or wheel centerline. The Outside Scrub or the outer most tire bulge is where we measure to get our Chassis Centerline. If the outside scrub radius is pushed out, it will lower your Swing Arm Angle initially as it extends from the outside scrub to the Instant Center. This intersection of the Swing arm and Chassis Centerline is our Roll Center. It should be slightly lower. Keep in mind, we have a Mac P strut up front that could interfere with any offset that could use a thicker tire but maintain the original OEM offset. As for the z28, I think 305's are enough this gen don't you.

Bumpsteer... Let's not go into this topic, it is frustrating at best if you have even the slightest idea. I am working on bump steer issues with 3 of our cars right now... As in... Still as of 1215am Wednesday... I will do some more measurements, recheck our tie rods via CAAL and go to sleep. I awake at 4:29 (yep, it's set there) and hopefully get our Camber/Caster/Toe adjusted tomorrow (today I guess). Scales again on Thursday...

Car 2 needs all kinds of sh!t done, motor mounts need repositioned, front suspension geometry done... I think the cross member needs notched... Can't remember... I heard Caster was 5 degrees which isn't a good thing for what we need it to do. Tight course and no long straights... Using a SLA w/Coilover so it isn't an issue.

Edit: scratch that... Moving your scrub out will raise your SAL angle not lower it.. My bad... This will raise you RC and help keep a 4200lbs car flat. You need to watch your Moment Arm Length though.

 

[JoeDogInKC]

My popcorn consumption continues to rise reading this thread, LOL!

 

[thePill]

Back to work!!!

 

[Stuntman]

Remember, your Swing Arm Length is measured from the Instant Center to the Outside Scrub Radius, not the tire or wheel centerline.

Wrong. The Front View Swing Arm Length (FVSA Length) is measured from the wheel centerline to the IC.

You can't determine your FVSA Length without knowing your IC, and I already outlined in posts 738 & 743 how to find your RC.

The Outside Scrub or the outer most tire bulge is where we measure to get our Chassis Centerline.

If the outside scrub radius is pushed out, it will lower your Swing Arm Angle initially as it extends from the outside scrub to the Instant Center. This intersection of the Swing arm and Chassis Centerline is our Roll Center. It should be slightly lower. Keep in mind, we have a Mac P strut up front that could interfere with any offset that could use a thicker tire but maintain the original OEM offset. As for the z28, I think 305's are enough this gen don't you.

Wrong.

Bumpsteer... Let's not go into this topic, it is frustrating at best if you have even the slightest idea. I am working on bump steer issues with 3 of our cars right now... As in... Still as of 1215am Wednesday... I will do some more measurements, recheck our tie rods via CAAL and go to sleep. I awake at 4:29 (yep, it's set there) and hopefully get our Camber/Caster/Toe adjusted tomorrow (today I guess). Scales again on Thursday...

Car 2 needs all kinds of sh!t done, motor mounts need repositioned, front suspension geometry done... I think the cross member needs notched... Can't remember... I heard Caster was 5 degrees which isn't a good thing for what we need it to do. Tight course and no long straights... Using a SLA w/Coilover so it isn't an issue.

Edit: scratch that... Moving your scrub out will raise your SAL angle not lower it.. My bad... This will raise you RC and help keep a 4200lbs car flat. You need to watch your Moment Arm Length though.

Wow, surprised to see some humility, but frightend that you're doing this kind of work on cars with what appears to be severe knowledge limitations.

...And the fact that you call Terry Satchell a moron (who wrote the chapter on suspension geometry in the father of vehicle dynamics' book) is beyond scary for your clients.

 

[thePill]

I think Terry needs to be more specific in his books. Nomenclature and the names of said components would be highly important in teaching literature.

They make it sound more complicated than it actually is...

Don't confuse my impatience with random internet know-it-alls with a lack of knowledge. Like Terry, being a sound Chassis Fab Engineer doesn't mean you can teach/instruct and write an articulate book. He's leaving things out because, quite frankly, it can't be written and taught. This is how I feel as well.

Does any of this help the z28 in any of the areas it falls short in as advertised? No, it's just a rubbish argument from a rubbish poster.

The fact that I have a person with no knowledge in these areas telling me I have no knowledge in these areas is...

Well... I'll just file it under "Rubbish".

 

[thePill]

Your clueless... You RC calculation is incorrect.

 

[Stuntman]

I think Terry needs to be more specific in his books. Nomenclature and the names of said components would be highly important in teaching literature.

They make it sound more complicated than it actually is...

Don't confuse my impatience with random internet know-it-alls with a lack of knowledge. Like Terry, being a sound Chassis Fab Engineer doesn't mean you can teach/instruct and write an articulate book. He's leaving things out because, quite frankly, it can't be written and taught. This is how I feel as well.

Does any of this help the z28 in any of the areas it falls short in as advertised? No, it's just a rubbish argument from a rubbish poster.

The fact that I have a person with no knowledge in these areas telling me I have no knowledge in these areas is...

Well... I'll just file it under "Rubbish".

" it can't be written or taught"? -I guess not if you don't understand it.

For the work you are doing, you really should own a few engineering books including this one.

Your clueless... You RC calculation is incorrect.

Its not "my" calculation but rather what is widely understood and accepted and written in many engineering books.

 

[Norm Peterson]

Originally Posted by thePill
Remember, your Swing Arm Length is measured from the Instant Center to the Outside Scrub Radius, not the tire or wheel centerline.

Wrong. The Front View Swing Arm Length (FVSA Length) is measured from the wheel centerline to the IC.

If we're going to get picky over the effect ~half a tire tread's width out of some multiple of track width has on the geo RC (which is mostly an analytical convenience), you need to start thinking of using some sort of force centroid location within the actual CP. Even if you don't do a full force-based analysis. Insufficient camber gain moves this outward (part of the reason why 5th gen Camaros beat up the outer couple of tire ribs when tracked hard with OE-ish camber and then some). Lateral tire distortion brings it back toward centerline for the outboard tire. Works opposite for the inboard tire.


Norm

 

[Stuntman]

^Same problem for stock camber on pretty much any strut. And why 305 front tires help greatly on the Z28. Still pretty amazing to see that tire width on a strut.

 

[thePill]

" it can't be written or taught"? -I guess not if you don't understand it.

For the work you are doing, you really should own a few engineering books including this one.

Its not "my" calculation but rather what is widely understood and accepted and written in many engineering books.

Sorry, your incorrect on multiple levels. The IC is NOT at the Chassis Centerline, this would produce two front roll centers from each suspension side. Depending on your Swing Arm, Tie/toe line and upper and lower link angles, your IC usually extends all the way out to the opposing suspension... The angle you suggesting would put your lower control arm angle NOT PARALLEL to the ground. Um hello? Anyone home?

I think your the only person on the planet who thinks weight doesn't roll around a center axis. Amazing!!!

Go seek an education...

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