S550 Mustang Suspension and Powertrain Discussion

[Sharad]

Can't wait to see which company is the first to throw out a set of polyurethane bushings for that front suspension.

I talked to Whiteline at PRI. They're chomping at the bit to produce a complete bushing upgrade.

We're planning to take a fairly archaic approach to the whole car (not just the suspension). We're going to beat on ours from day one and upgrade anything that breaks. I guess you'd call that field testing?

 

[NUTCASE]

that is the best idea IMO. change what needs to be changed, avoid over complication and R&D into parts that don't do much.

 

[Department Of Boost]

Frankly, I won't be surprised if the amount of difference in the handling between the S550 and the S197 on the track comes down to differences in the size of the tires, the effective wheel rates in various regimes, the front:rear grip balance dialed in, differences in CG and roll centers, and AS properties.

Which is to say, I somehow suspect that the IRS isn't going to make much of a difference on the track except possibly when comparing stock with stock.

But then, maybe that's because I own an S197.

Sure is going to be interesting to see just what can be done with the IRS in the S550, though.

Add some bumps/imperfections on corner exit and the S550 will leave the S197 to tie itself in knots.

 

[07TGGT]

Frankly, I won't be surprised if the amount of difference in the handling between the S550 and the S197 on the track comes down to differences in the size of the tires, the effective wheel rates in various regimes, the front:rear grip balance dialed in, differences in CG and roll centers, and AS properties.

Which is to say, I somehow suspect that the IRS isn't going to make much of a difference on the track except possibly when comparing stock with stock.

But then, maybe that's because I own an S197.

Sure is going to be interesting to see just what can be done with the IRS in the S550, though.

The 2015 isn't out yet. Have you tested the two in a stock configuration and compared them? Don't think so. So why not just not say some pretty stupid assumptions again...

You also do know they benchmarked it vs against the Boss 302 and surpassed it right?

 

[sheizasosay]

Add some bumps/imperfections on corner exit and the S550 will leave the S197 to tie itself in knots.

+1
Improvement on the track with the right conditions. Big improvement on the street. I bet the amount of accidents will go down.

 

[Gray Ghost GT]

Add some bumps/imperfections on corner exit and the S550 will leave the S197 to tie itself in knots.

I'm looking forward to the S550 platform with the new IRS setup and all the aftermarket upgrades that will become available to enhance its handling for the road courses! Attacking the apex and riding the rough gator curbing with some negative camber dialed in the rear, should provide the driver with much more confidence and consistency because of improved traction in the turns and esses. Hope to have one in my garage in 2016.

 

[kcbrown]

Add some bumps/imperfections on corner exit and the S550 will leave the S197 to tie itself in knots.

That's certainly possible.

But don't you still have a sway bar in the rear on the S550?

If so, then wouldn't that effectively link the two sides and result in at least some of the same sort of problem?

 

[kcbrown]

The 2015 isn't out yet. Have you tested the two in a stock configuration and compared them? Don't think so. So why not just not say some pretty stupid assumptions again...

I'm not claiming that there won't be any difference, just saying that I won't be surprised if the difference proves to be less than some seem to expect.

I mean, the C6 Corvette has a lower CG, an independent rear suspension, and is lighter, and yet, isn't the Mustang with proper springs, dampers, and setup able to keep up with it? If so, then why, unless the IRS doesn't make that much of a difference? Power? What explains that a Mustang GT with equal weight and equal power is in stock form able to keep up with a BMW M3 on the track despite its dampers being garbage and its stick axle (versus the M3's IRS)?

I'm not saying this to be argumentative -- I really want to know why properly set up Mustangs seems to do so well against cars that have IRS if IRS really makes such a huge difference.

You also do know they benchmarked it vs against the Boss 302 and surpassed it right?

By how much? Under what conditions?

And what does the data say about the reason it did better than the Boss 302?

 

[Swine]

Yeah its possible the IRS is more of a refinement then a game changer. The biggest difference for me would be would be the ability to dial in an alignment.

 

[Norm Peterson]

Add some bumps/imperfections on corner exit and the S550 will leave the S197 to tie itself in knots.

But don't you still have a sway bar in the rear on the S550?

If so, then wouldn't that effectively link the two sides and result in at least some of the same sort of problem?

Yes, but "some of the same" ends up being closer to "a very small amount of the same". There is more to this than just the stiffness comparison between an IRS sta-bar and an 8.8" stick axle.


Norm

 

[Norm Peterson]

The biggest difference for me would be would be the ability to dial in an alignment.

Within limits and with some difficulty this can be accomplished with stick axles . . .


As far as the IRS being clearly superior - that comes down to its specific tuning, not its mere presence. It wasn't until the 1LE that any normally aspirated Camaro could claim to have better handling than what you could get in a non-Boss GT. And much of that superiority came from the 1LE having a better wheel/tire package.


Norm

 

[modernbeat]

Add some bumps/imperfections on corner exit and the S550 will leave the S197 to tie itself in knots.

I expect that will be true. And I'm looking forward to it. But one of the things that always surprises riders in our current track car is how composed it is over extremely bumpy sections of track. Many times people just "knew" the car wouldn't be able to handle the rough sections that upset their Corvette or EVO as we drive right over them while putting the power down.

 

[Gray Ghost GT]

I expect that will be true. And I'm looking forward to it. But one of the things that always surprises riders in our current track car is how composed it is over extremely bumpy sections of track. Many times people just "knew" the car wouldn't be able to handle the rough sections that upset their Corvette or EVO as we drive right over them while putting the power down.

There's something to be said about the "nut behind the wheel"; the best performance modification is the "driver mod"

 

[kcbrown]

Yes, but "some of the same" ends up being closer to "a very small amount of the same". There is more to this than just the stiffness comparison between an IRS sta-bar and an 8.8" stick axle.

Please elaborate. One of the reasons I love this forum is that it's so educational, and this seems like an excellent opportunity for such!

It seems to me that the two major differences between IRS and stick axle are, firstly, that motion on one side of the car will cause camber changes to the other side and, secondly, that the unsprung weight is significantly higher with the stick axle.

I can see how the camber changes would introduce cornering instability, but I don't know how much instability we're talking about here.

 

[Gray Ghost GT]

The IRS provides better ride quality and handling characteristics, due to lower unsprung weight and the ability of each wheel to address the road undisturbed by activities of the other wheel. The lower unsprung weight of an IRS relative to a live axle design is due to the differential unit not forming part of the unsprung elements of the suspension system. Instead it is either bolted directly to the chassis or subframe. High unsprung weight also exacerbates wheel control issues under hard braking. I can feel these differences when driving the Mustang vs. the Corvette. The IRS gives you better traction, control and confidence to push a little harder through the turns and esses. IRS also provides better trail-braking, allowing you to go deeper into the corner with little to no detectable wheel hop.

 

[ArizonaGT]

Additional minor benefit: no pinion angle adjustments/fine tuning required for lowered vehicles or lightweight driveshafts.

 

[05yellowgt]

Additional minor benefit: no pinion angle adjustments/fine tuning required for lowered vehicles or lightweight driveshafts.

No more heavy telescoping driveshafts!!!!

Sent from my Transformer Prime TF201 using Tapatalk 4

 

[Whiskey11]

We certainly don't want to forget that a live axle setup has different roll and bump spring rates which makes damping a much larger compromise than with an IRS which is a little closer to each other.

One thing is certain, I wouldn't expect a stiffly sprung IRS car to handle bumps like a properly setup live axle car (the term "stiffly sprung" for a live axle is relative). I would probably still give the nod to the IRS but I think both will equally suck over bumps!

 

[Norm Peterson]

It seems to me that the two major differences between IRS and stick axle are, firstly, that motion on one side of the car will cause camber changes to the other side and, secondly, that the unsprung weight is significantly higher with the stick axle.

I can see how the camber changes would introduce cornering instability, but I don't know how much instability we're talking about here.

I was only looking at stiffness effects. It's obvious that the unsprung mass matter (and its mass moment of inertia term as well) favors independent suspensions. I'm only going to mention that part in passing. A sta-bar introduces force, stiffness, and mass effects.

The main effect that a sta-bar will have is momentary unloading of the wheel not being 'bumped' (which will tend to reduce its grip and let it slip a bit more, this being an oversteerish effect).

Sta-bar stiffness effect on wheel cambers should be minimal with IRS, and may actually be trying to help the inside wheel camber situation a tiny bit on a stick axle while hurting the IRS's inside wheel camber (also only by a small amount).

A separate small sta-bar effect is that some of the bar is sprung mass, which affects suspension behavior as damped vibrations. IRS bars and bars like the S197's OE rear bar don't add as much as bars like the Whiteline, but at least this is a minor effect compared to the mass and mass moment of inertia of the 8.8 axle assembly with brakes and wheels/tires.

I doubt that any bump that doesn't launch the bumped wheel clear of the ground will affect stick axle camber by more than about a degree . . . I'm estimating this based on the tire in 'bump' displacing upward an amount equal to its static deflection under the corner weight here and a rear track of at least 57.3" . . . from there you'd have to have proprietary tire grip vs camber curves to estimate what this might mean to the car's overall behavior.


Norm

 

[SoundGuyDave]

I expect that will be true. And I'm looking forward to it. But one of the things that always surprises riders in our current track car is how composed it is over extremely bumpy sections of track. Many times people just "knew" the car wouldn't be able to handle the rough sections that upset their Corvette or EVO as we drive right over them while putting the power down.

Part of that may be the old "self-fulfilling prophecy." I *KNOW* that my car won't handle well under power over the bumps, so I puss out... That reduces transfer to the rear, and thus load on the rear tires, possibly exacerbating the situation.

Also GOOD dampers help a LOT with this situation, compared to the run-of-the-mill Koni/Tokico/Bilstein offerings.