Why did the 6th gen SS 1LE get wider tires at the rear only?

[Boost Creep]

My thinking is, the Alpha chassis with the LT1 engine must tend to oversteer, and adding more rear grip eliminates the oversteer and gives a little understeer which is what a lot of people desire for more predictable handling.


Just my guess.

[Norm Peterson]

Originally Posted by vtirocz

This question was asked to Al during the last Camaro Fest in Bowling Green. He said that they tested several different options, including a square setup like the 5th gen SS 1LE, and they were able to get faster lap times and overall better handling characteristics with the setup they chose. The practical benefits of the square setup were offset by the better performance characteristics of the staggered setup.

Keep in mind that the 6th gen suspension geometry and chassis are different from the 5th gen, so what worked well on one may not work well on the other.

Originally Posted by Boost Creep

My thinking is, the Alpha chassis with the LT1 engine must tend to oversteer, and adding more rear grip eliminates the oversteer and gives a little understeer which is what a lot of people desire for more predictable handling.

Kind of what I want to hear from those who know what went on during development. It's why I mentioned a number of specific items. I realize that the chassis is different, as are the tires, and possibly the weight distribution.

It would be interesting as well to know whether lap times improved more by being able to put the power down better, or if the improvement was more evenly split between acceleration and cornering/handling. Maybe some sort of %slip vs slip angle thing???


Norm

[Ryephile]

Originally Posted by Norm Peterson

Kind of what I want to hear from those who know what went on during development....

I'm not sure what you're asking is legally savvy, with corporate umbrella NDA's so prominent these days. It's certainly not business-ethically reasonable for a development engineer to spill all the I.P. beans in a public venue.

[Norm Peterson]

Originally Posted by RacerX78

Well given that the 5th and 6th Gen cars are on completely different chassis, engine, and suspension. It doesn't make since to compare the two.

We can go either of two ways here . . . either blindly accept "it's because they're different" and dismiss the whole thing while learning nothing, or try to get to another level of detail that might be useful. What was it that made the 285/305 on 10/11 combination better? Or alternatively, why wasn't the previous 285/285 on 10/11 combination as good? Yes, I'm aware that there is a 5-point profile difference.

A closer comparison would be between the ATS-V and the Camaro given they are on the same platform.

Perhaps so, but the missions of those two cars differ, where the missions of the 5th gen and 6th gen Camaros are the same. Cadillac vs Camaro, you'd tune for a different compromise between ride and handling.


I don't want to drag this off-topic with comparisons to the various Mustang generations beyond noting that the S197 doesn't have much in common with the SN95 (which was an evolution of the Fox . . . i.e. Fairmont). The 5th and 6th gen Camaros are more alike than the SN95 and S197 (never mind the S550 to any previous Mustang).


Norm

[Norm Peterson]

Originally Posted by Ryephile

I'm not sure what you're asking is legally savvy, with corporate umbrella NDA's so prominent these days. It's certainly not business-ethically reasonable for a development engineer to spill all the I.P. beans in a public venue.

Answers in reference to the list in post #1 ought to be do-able as long as specific (design-basis?) numbers aren't disclosed.

Though we did get more detail in the answer to the launch control question than I had expected, so it's a bit of a guess how much detail might be given if this question gets picked.


Norm

[Mr. Wyndham]

Originally Posted by Norm Peterson

Given that the 5th gen 1LE and Z/28 both ran same-size tires at all four corners, I'm wondering what changed the philosophy specifically for the 6th gen SS 1LE away from maintaining the same tire size all around and simply making the rear wheels a little wider than the fronts.

Was it a downstream consequence of the bump in power and torque? Understeer budget or breakaway characteristics reasons and the Alpha chassis? Appearance? Other?


Norm

Very interesting question!

From the engineers' standpoint, a detailed response could speak a lot about the Alpha platform dynamics and LT1 power to the ground!

[RacerX78]

Originally Posted by Norm Peterson

We can go either of two ways here . . . either blindly accept "it's because they're different" and dismiss the whole thing while learning nothing, or try to get to another level of detail that might be useful. What was it that made the 285/305 on 10/11 combination better? Or alternatively, why wasn't the previous 285/285 on 10/11 combination as good? Yes, I'm aware that there is a 5-point profile difference.



Perhaps so, but the missions of those two cars differ, where the missions of the 5th gen and 6th gen Camaros are the same. Cadillac vs Camaro, you'd tune for a different compromise between ride and handling.


I don't want to drag this off-topic with comparisons to the various Mustang generations beyond noting that the S197 doesn't have much in common with the SN95 (which was an evolution of the Fox . . . i.e. Fairmont). The 5th and 6th gen Camaros are more alike than the SN95 and S197 (never mind the S550 to any previous Mustang).


Norm

My is that because of the vast differences between the two generations there were cometeply different needs and restrictions that the engineers hand to deal with.

Need - Get as much mechanical grip as possible F&R, using better a better chassis, suspension and tires.
Restriction - Physical size constraints, 285s on 20s in the front are already very close to the suspension and fender. (ZL1 1LE has narrower springs, wider finders & shorter rims.)

[Norm Peterson]

Originally Posted by RacerX78

My is that because of the vast differences between the two generations there were cometeply different needs and restrictions that the engineers hand to deal with.

It's still the same problem to be solved, just with slightly different details and/or constraints. So I'm a little surprised that the SS 1LE didn't end up closer to the 5th gen Z/28 in this respect - even the LS7 and LT1 torque figures aren't all that much different like they are between the LT1 and the current ZL1. The SS 1LE could have run on 19" rolling stock too, but didn't.


Norm

[RacerX78]

Originally Posted by Norm Peterson

It's still the same problem to be solved, just with slightly different details and/or constraints. So I'm a little surprised that the SS 1LE didn't end up closer to the 5th gen Z/28 in this respect - even the LS7 and LT1 torque figures aren't all that much different like they are between the LT1 and the current ZL1. The SS 1LE could have run on 19" rolling stock too, but didn't.


Norm

Thats according to you. Just because it has the same FR layout and number of doors. Doesn't mean its dealing with the same type challenges.

Just understand that the 1LE had different challenges and different goals in the end. And from the looks of it, the performance goals were met.

[WhyUMad1LE]

5th gen SS had more understeer.

[Norm Peterson]

Originally Posted by WhyUMad1LE

5th gen SS had more understeer.

If we're lucky, maybe Al can find a way to incorporate your Chassis Torsional Stiffness question into this (and kill two birds with the same stone).


Norm

[Ryephile]

Originally Posted by Norm Peterson

If we're lucky, maybe Al can find a way to incorporate your Chassis Torsional Stiffness question into this (and kill two birds with the same stone).


Norm

That figure is totally in the noise compared to the dynamic wheel rates. A 300 Lb/In wheel rate pales compared to a 30,000 N/° torsional stiffness (as generic but realistic examples).

The plain fact is the 5th gen was tuned via springs and sway-bars to have a different at-limit characteristic [more understeer] than the 6th gen, despite having wider front tires. For a wider front tire to understeer, you need either a stiffer front ARB, or a softer rear ARB. Or you need less optimal front camber curve to reduce the contact patch up front at the limit, possibly combined with a very good camber curve in back to enhance at-limit grip of the rear tires. Or quick-acting bumpstops up front versus relatively non-active rear bumpstops. There are at least a handful of ways to tailor the response *after* you chose tires.

It feels like you're trying to narrow down the entire suspension calibration to one facet. It's definitely not that simple.

[Ventura 1LE]

Originally Posted by RacerX78

My is that because of the vast differences between the two generations there were cometeply different needs and restrictions that the engineers hand to deal with.

Need - Get as much mechanical grip as possible F&R, using better a better chassis, suspension and tires.
Restriction - Physical size constraints, 285s on 20s in the front are already very close to the suspension and fender. (ZL1 1LE has narrower springs, wider finders & shorter rims.)

I can tell going from 15 LE to 18 SS 1 LE.. The SS 1LE at Autoclub Speedway Roval after the tires were heated it produced more understeer than desired with mode set on full track. I dont know if the 285s upfront causing it with ELSD keeping my rear in check but the 15 1LE was more tolarable in understeer on the square setup.

Im thinking to promote less understeer on the 18 SS 1LE is to do more late braking. Thus having better weight on the front until mid turn and gas a bit harder before understeer is pushing me out to the corner exit. In essence having the rear turn with throttle steering working in my favor.

If that does not work then change to a square setup with wheel spacers up front running 305s on track wheels. Also adding a front splitter extension and dive planes for more downforce...

Too me it seems the rear is planted and not the issue.. the 285s/305s non square is.. but if that changes during my experiment add the wicker bill. I will accept more drag on straight line speed.

Note: the 285s on 11s is a bit of a sidewall issue with me on exposure of the edge of the rim and streching for most tires. I can add rock guards to deflect most of rocks hitting the side of my car with the 305 square setup with wheel spacers added for clearance of front struts. Then agian leave everything as is and adjust my driving knowing the limits the car has or likes.