Autocross Thoughts

[Areddi]

Active autocrosser in the WDCR SCCA region, currently running an FR-S in STX. I have own two Mustangs before, an 89' 5.0 and an 00' GT, and am considering getting back into the Mustang game with the 15'.

Autocross is my primary focus for racing and entertainment, and I was curious to poll the group and see if anyone else is planning on getting a 15' for that purpose, and what your thought process is?

To me my mustang has to have the V8, but the EcoBoost option could be a killer with a tune in an ST class with the weight savings and the low end torque output. Any thoughts on this?

This season the current coyote was moved into STU, so I would assume the 15' coyote would move there as well. Think an EcoBoost equipped car would fall into the same category, or would SCCA class it differently based on the theorized power outputs? What about street classes?

Thanks for any thoughts any of you fellow autocross guys may have, on any of those items, as well as anything related to the suspension now since the car is moving to IRS.

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[Whiskey11]

Active autocrosser in the WDCR SCCA region, currently running an FR-S in STX. I have own two Mustangs before, an 89' 5.0 and an 00' GT, and am considering getting back into the Mustang game with the 15'.

Autocross is my primary focus for racing and entertainment, and I was curious to poll the group and see if anyone else is planning on getting a 15' for that purpose, and what your thought process is?

To me my mustang has to have the V8, but the EcoBoost option could be a killer with a tune in an ST class with the weight savings and the low end torque output. Any thoughts on this?

This season the current coyote was moved into STU, so I would assume the 15' coyote would move there as well. Think an EcoBoost equipped car would fall into the same category, or would SCCA class it differently based on the theorized power outputs? What about street classes?

Thanks for any thoughts any of you fellow autocross guys may have, on any of those items, as well as anything related to the suspension now since the car is moving to IRS.

Avid autocross here myself, was in STX last year and ran at Nationals in STX in my 2009 Mustang GT. I think that if Ford keeps the weight down the 2.3L mill is going to be a solid car for STX. I don't anticipate it ever being placed there though. I get the distinct impression that they will do some voodoo magic and change the last number in the year for Mustangs to 2015 (N/A) and keep the turbo mills out of ST. If it does get put in STU, I think it'll be a VERY strong contender for the boost buggies and only gives out in width and weight to them.

The problem I see right now is weight. We have no idea what the curb weight of the 2015 Mustang will be. If Ford doesn't shed some weight I think the whole line is going to be pretty status quo in the performance department with the current cars. IRS might help some but the added width wont help the car at all. What I would like Ford to do is put the EB4 at around 3200-3300lbs, the GT around 3400-3500lbs (erring on the 3400lbs side). With the roughly ~170-200lbs of fluff in most modern cars that is legal to remove in ST that would put your EB4 in the 3000-3100lb range and depending on what the power output is, somewhere in the 330RWHP-330RWTRQ range. That screams domestic 350Z to me and we know how that is working out in STU.

As for street classing, I'm predicting the coyote will stay in F-Street with the E9X M3's since they are going to be frighteningly similar cars. I wouldn't be surprised if the 2.3L will be with some of the lesser E9X chassis cars wherever they are at (BS?).

I'm not quite as thrilled about the switch to an IRS. About the only gains I think we'll see are going to come from the massive expansion of the rear track and the new front suspension. I "guess" one bonus is I can spend the $1700 worth of live axle specific suspension parts on higher end coilovers and a better diff since I don't really need to dick around with huge swings in geometry causing significant loss of rear traction. Dynamic camber gain might save the tires some and give me a little more cornering speed but really the biggest advantage of the IRS is the better ride quality which I'll promptly toss out the window with stiff springs!

 

[Areddi]

I like all of your thought there. Do you think that both the EB4 and the Coyote would go into STU? I guess then like you said it would come down to weight. if the Coyote ends up in the 200 lbs heavier range, I don't know if the power output over the EB4 will be worth it versus the nimbleness.

I suppose it matters what is available as a factory option as well, i.e. I heard that the car can be had as a "GT" with either powerplant so you get all the goodies to go along with that. If you have to go Coyote to get a GT or the track pack option, than that changes the game. Maybe an EB4 Mustang called the Mustang ST, and then the coyote is the GT?

 

[Whiskey11]

I like all of your thought there. Do you think that both the EB4 and the Coyote would go into STU? I guess then like you said it would come down to weight. if the Coyote ends up in the 200 lbs heavier range, I don't know if the power output over the EB4 will be worth it versus the nimbleness.

I suppose it matters what is available as a factory option as well, i.e. I heard that the car can be had as a "GT" with either powerplant so you get all the goodies to go along with that. If you have to go Coyote to get a GT or the track pack option, than that changes the game. Maybe an EB4 Mustang called the Mustang ST, and then the coyote is the GT?

I know there is a performance package option for both. On the 2.3L it gives you the brakes off of the base GT with the 14in rotors and four pot fixed calipers. I don't think it gives you the same spring rates and dampers but they will be better than standard. We'll see. I don't know if they will be worth it on an ST autocross only car.

 

[Areddi]

Yeah I mean you figure you're going to upgrade all of that aftermarket anyway, unless of course the factory brakes are already that good.

I am getting excited to see the numbers on weights, power, and specific options. Really think this thing could be a stout competitor, but like you said, weight will be key.

 

[Norm Peterson]

I'm not quite as thrilled about the switch to an IRS.

With IRS you "gain" the lower rear geometric roll center height, which tends to make the percentage of roll resistance through the front and rear roll centers more similar than they are in the usual stick axle setups. Likewise, the percentages of roll resistance taken elastically (springs/bars/dampers) are also more similar. During transients, the handling balance due to lateral load transfer shifts less.


Norm

 

[GMAN6]

Norm, would you agree that how an IRS handles on the track depends on how it's set up?

Would you agree that every IRS doesn't outperform every straight axle?

I don't pretend to be an expert on track cars, but I have seen many straight axle cars outperform IRS cars at racing events. Now, with that being said, I do believe that the optimal IRS will outperform the optimal live axle.

My thought is that no DD factory street car is set up for optimal handling. It's always a compromise between comfortable ride quality and handling. So my thought is that the greatest advantage of the IRS, for your average owner, is that it will allow for better handling without sacrificing as much ride quality.

 

[Norm Peterson]

Norm, would you agree that how an IRS handles on the track depends on how it's set up?

Would you agree that every IRS doesn't outperform every straight axle?

I can't remember how many times I've posted that a well-done stick axle beats an indifferently done IRS, or words to that effect. With IRS there are more variables that you can play with to achieve your goals, which can be a two-edged sword.

My thought is that no DD factory street car is set up for optimal handling. It's always a compromise between comfortable ride quality and handling. So my thought is that the greatest advantage of the IRS, for your average owner, is that it will allow for better handling without sacrificing as much ride quality.

Probably. But for the true "average" driver (as opposed to the average performance driver) most of the benefit is going to be on the ride quality side. John and Jane Average don't drive hard enough for handling balance short of truly evil to have any meaning, and good handling to them means it doesn't feel like it takes half an acre to make a parking lot U-turn in.


Norm

 

[GMAN6]

Exactly what I think.

The stick axle handles way better than the average driver will need, so the only real advantage to the AVERAGE driver will be ride quality and bragging rights.

 

[IGJoe2192]

Stick axles can handle well yes, but they are at a disadvantage when they run into bumps mid corner. A stick axle will become unsettled when encountering these bumps. This is something I have experienced first hand during spirited driving. On to the IRS, if it is a good setup, it will not become unsettled by mid corner bumps, which means better grip, more driver confidence and faster corner exit speeds, which all means faster lap times. Being an all new chassis it will be hard to tell where the actual improvements are, is it the suspension? Is it lighter weight? Is it more power? Or is it the combination of two or more of those. I am eagerly awaiting the many articles that are in review of this new platform. I believe this new platform will be excellent for autocross, especially the EB with PP.

 

[Norm Peterson]

Stick axles can handle well yes, but they are at a disadvantage when they run into bumps mid corner.

Of course.

But I think the ride discomfort will still bother Joe Average enough to slow him down the next time he takes the same bumpy corner before it threatens to spit him off the black part. Staying on line at autocross and on real road courses may be a different story, either quite smooth where the issue doesn't come up or maybe not so smooth and you might try a slightly different line.


Norm

 

[Whiskey11]

Of course.

But I think the ride discomfort will still bother Joe Average enough to slow him down the next time he takes the same bumpy corner before it threatens to spit him off the black part. Staying on line at autocross and on real road courses may be a different story, either quite smooth where the issue doesn't come up or maybe not so smooth and you might try a slightly different line.


Norm

Norm, how much of this "discomfort" is, in your opinion, a product of lateral displacement of the axle under the car? I've put a number of highly talented drivers in my car (watts link, Fays2, rod ends) who were shocked when told that the car had a live axle. Most commented about the mid corner composure and grip that they did not expect from a live axle car. A few mentioned how capable the car is at soaking up the bumps.

A large portion of me feels that the rapid upward/downward displacement due to bumps moving the axle laterally contributes a lot to the discomfort some driver's feel as the 300lbs of axle shifts laterally under the car like a giant pendulum. That issue is less evident when that lateral displacement is drastically minimized or removed. If I can make an educated guess, that would mean that one wheel bump isn't going to upset the chassis as much since your loading doesn't change as much in one wheel bump. In two wheel bump you don't have that lateral displacement in the axle too.

At that point it would take a large vertical displacement to really upset the contact patch significantly wouldn't it? While it wouldn't be ideal since one tire does see some change in load regardless of PHB vs. Watts link, I do see it eliminating 90% of the "hop because of mid corner bump" nonsense. I will say that of all the autocross cars I've driven in anger, all of them responded pretty poorly to decent sized mid corner bumps. I'm struggling to think of a single car that didn't... IRS or live axle.

 

[Shark77]

I've never done autox but I've had a lot of laps on tracks. My experience with the IRS vs. SRA is this:

SRA can handle quite well but isn't as flexible in track changes and mixing up lines. When I've run cars with SRAs, I found that changing up lines really messed with lap times. However, when running cars with IRS, they had more flexibility to run different lines without sacrificing as much lap time. - This is just my anecdotal experience. I've seen plenty of SRA cars run amazing laps, my criticism is only in their flexibility to change to conditions on track. They just don't seem to have the same flexibility in general... There are always outliers.

 

[Norm Peterson]

Norm, how much of this "discomfort" is, in your opinion, a product of lateral displacement of the axle under the car? I've put a number of highly talented drivers in my car (watts link, Fays2, rod ends) who were shocked when told that the car had a live axle. Most commented about the mid corner composure and grip that they did not expect from a live axle car. A few mentioned how capable the car is at soaking up the bumps.

A large portion of me feels that the rapid upward/downward displacement due to bumps moving the axle laterally contributes a lot to the discomfort some driver's feel as the 300lbs of axle shifts laterally under the car like a giant pendulum. That issue is less evident when that lateral displacement is drastically minimized or removed. If I can make an educated guess, that would mean that one wheel bump isn't going to upset the chassis as much since your loading doesn't change as much in one wheel bump. In two wheel bump you don't have that lateral displacement in the axle too.

At that point it would take a large vertical displacement to really upset the contact patch significantly wouldn't it? While it wouldn't be ideal since one tire does see some change in load regardless of PHB vs. Watts link, I do see it eliminating 90% of the "hop because of mid corner bump" nonsense. I will say that of all the autocross cars I've driven in anger, all of them responded pretty poorly to decent sized mid corner bumps. I'm struggling to think of a single car that didn't... IRS or live axle.

I think I'd file lateral axle displacement effects under uneasiness or uncertainty [about what's going on back there and where it might be trying to steer me] rather than physical discomfort (which is mainly a matter of vertical acceleration and jerk). There may also be a fore-aft acceleration component of discomfort as well, if drive traction is varying widely due to recurring traction loss.

Harshness seems to be the big part of discomfort, and I just don't see the lateral effects being 'harsh'. Firmer but better controlled with aftermarket PHB arrangements vs softer with a little less control due to greater displacement (from bushing compliance) with OE, probably, and why an aftermarket PHB might at least feel a bit different.

There are at least two other effects on the opposite side tire from one wheel bumps. There will be a slight camber change (about a degree per inch of bump, more than enough to drive it into a +camber condition), and the axle itself sees vertical and rotational accelerations as a rigid body (think front or rear view here), all of which will instantaneously affect the off-side tire's grip. Affecting grip affects slip angle, which out near the limit will definitely get your attention, where at 2/10ths or so on the street you probably wouldn't notice.


Norm

 

[Areddi]

So there was a recent article about the EB4 that has been circulating around. Looks like it is good, but at least in initial review, not a knock-out over the V6, and perceivably not within reach of the V8. Seeing some of the features in the Performance Pack, now that we have seen that, the V8 is looking more appealing.

Curious if anyone's thoughts have changed with these updates we've seen in the past week.

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