IRS and Front End Rise Question

[motorjock205]

OK, I am 61 years old and new to the IRS in the 15-18 Mustangs, but after doing a few updates on the wife's car this past weekend and taking the car out for a test drive, I am wondering how to keep the front end down at high speeds...I got the car up to about 150 MPH and the front end just felt very light and high up in the air...I know the IRS allows these things to squat more in the rear, but at high speed, a light front end kinda makes me nervous...Any help would be appreciated...I know you young guys can steer me straight on this. I will add that we just put new Cooper RS G3 235 18 tires on the car and I also replaced the brake pads...Car has just shy of 30K miles. I wouldn't think that the struts would be worn enough to let the front end go up so much, as they seem tight when I push on the fenders.

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[BmacIL]

Well a front splitter would help, but that's not really where the floaty feeling stems from.

The base dampers are not very good for anything other than a super cushy ride and certainly no good for controlling the body motions in a way that feels good at those speeds. There are a few things to improve the way the car handles speed:

1. Damper upgrade
- Ford Performance Track dampers or Steeda non-adjustable Pro Actions
2. Front end chassis bracing
- Doing everything listed here makes a quite substantial difference in composure and feel, without a ride penalty (actually an improvement, IMO): https://www.mustang6g.com/forums/th...ion-lower-k-brace-install-guide.100800/unread
3. Rear subframe control
- BMR CB762 + CB010 will drastically limit subframe movement and make the rear feel connected to the rest of the car. They also reduce wheel hop and improve your ability to put power down on corner exit
4. Mild lowering
- If you're able to or want to lower the car, a little bit of lowering with the above dampers makes the car feel much more planted. BMR SP763 would be my recommendation.

I would do 1 and 2 at a minimum, and 4 is best to do when doing #1.

 

[motorjock205]

Thanks for the reply BmacIL, I don't think I will be lowering it any, I'm 6'3 on top of being 61 years old, and have a hard enough time getting in and out as it is...LOL But I can certainly look at changing some dampers and I have been looking at the K-Member bracing up front. I have installed a GT Strut Brace and Firewall Brace so far, but looking to do a little more down below.

I remember driving my 2008 Shelby GT without a rear spoiler at high speeds, and it was totally different...the rear end was moving around, so I added a GT500 rear spoiler, and it was GREAT after that!

 

[Zinc03svt]

You did not give us much info on your car Bud. I’m guessing base suspension and wheels. That is pretty fast @ 150 mph. Have you owned it since new?

I have had my 18 GT pp1 car up to just shy of a buck forty and car felt fine. Felt like it would handle 170 mph no problem.

 

[BmacIL]

Thanks for the reply BmacIL, I don't think I will be lowering it any, I'm 6'3 on top of being 61 years old, and have a hard enough time getting in and out as it is...LOL But I can certainly look at changing some dampers and I have been looking at the K-Member bracing up front. I have installed a GT Strut Brace and Firewall Brace so far, but looking to do a little more down below.

I remember driving my 2008 Shelby GT without a rear spoiler at high speeds, and it was totally different...the rear end was moving around, so I added a GT500 rear spoiler, and it was GREAT after that!

The firewall connector (you can't see it with everything assembled) is more important than most people realize and surprised me with its change to the car. It connects the large upper K-brace (between strut towers and cowl) to the actual dash panel structure and closes the box there. It is standard on every car with the Perf Pack.

The dampers will help settle the car at higher speeds, and you may want to look at the ZL1 add-ons splitter if that is going to be a regular thing.

 

[JCFoster]

Just a thought, if the tires were brand new they could be slippery at first especially with the cool temps. I too have a ‘16 and at 140 the front end felt pretty stable.

 

[motorjock205]

Thanks for the reply BmacIL, I don't think I will be lowering it any, I'm 6'3 on top of being 61 years old, and have a hard enough time getting in and out as it is...LOL But I can certainly look at changing some dampers and I have been looking at the K-Member bracing up front. I have installed a GT Strut Brace and Firewall Brace so far, but looking to do a little more down below.

I remember driving my 2008 Shelby GT without a rear spoiler at high speeds, and it was totally different...the rear end was moving around, so I added a GT500 rear spoiler, and it was GREAT after that!

Yes, Base GT with 18" wheels and tires. I am not used to the amount of "squat" that the rear end does with the new IRS. I've always been a solid axle guy...I know they are harder to get to grip, but seem to be better at sustained high speed. Just my opinion though.

 

[motorjock205]

The firewall connector (you can't see it with everything assembled) is more important than most people realize and surprised me with its change to the car. It connects the large upper K-brace (between strut towers and cowl) to the actual dash panel structure and closes the box there. It is standard on every car with the Perf Pack.

The dampers will help settle the car at higher speeds, and you may want to look at the ZL1 add-ons splitter if that is going to be a regular thing.

I didn't install that firewall connector when I installed the brace and strut bar...I had no idea where it went or how to install it, but now that I have seen a post on how to install it, I will get it added sometime soon. I'm sure 150 will not be a regular thing...I was just surprised at how much more the car seemed to have waiting to be unleashed...If I am not mistaken, the car shifted into 5th then 6th after I let off at that speed...would be nice to have a 200 MPH speedo in the car just to find out some day...LOL Once I get the front end issue solved mind you...

 

[Cobra Jet]

Seeing you have a 2016 based on your profile, in the event you don’t know this small fact - the front ends of the 2015-2017’s will seem “floaty” more so because of the design of the front sheet metal, particularly the hood.

At the speed you were driving on a public roadway (*be careful doing that on public roads....) - you should have noticed considerable hood lift and flutter.

The 2015-2017’s suffer from hood flutter even at sustained speeds of 65-75mph. Due to the overall design of the 2015-2017 front end, it appears from the driver perspective as if the front is higher or is “lifting” when the rear end squats down on acceleration.

The 2018-19’s, Ford downsloped the entire front end from the inner fender rails, the front core support and outer sheet metal (hood/fenders). The redesign remedied the excessive hood flutter (none at all) and when a 2018/19 accelerates, even with hard launches or at excessive speed the front end is more planted not only physically but from an aesthetics point of view from the driver seat.

You can do as others have said by using aftermarket suspension components to bring down the center of gravity or to improve overall handling - but the high or floaty front end may remain due to how the 2015-17 was designed and how the hood is interacting with wind shear.

The 2015-17 front end looks really long (and high) from the driver seat. I’ve owned a 2016 and coming into the 2018, there are vast differences not only visually but also from a handling perspective. Other earlier posts on this site from owners who have went from an early S550 into a 2018/19 have also posted similar experiences regarding overall STOCK handling characteristics and the view from the driver seat. Of course anyone who has not owned any S550 prior to 2018 will always think the stock suspension still needs improvements.

Not discounting any suspension characteristics that you’re actually feeling, but that 2015-17 high hood line adds to the floaty feeling - because even with a great suspension, the hood looks so long even when going into curves, it appears the front of the car is still plowing into or not following the curve... LOL.

 

[BmacIL]

Seeing you have a 2016 based on your profile, in the event you don’t know this small fact - the front ends of the 2015-2017’s will seem “floaty” more so because of the design of the front sheet metal, particularly the hood.

At the speed you were driving on a public roadway (*be careful doing that on public roads....) - you should have noticed considerable hood lift and flutter.

The 2015-2017’s suffer from hood flutter even at sustained speeds of 65-75mph. Due to the overall design of the 2015-2017 front end, it appears from the driver perspective as if the front is higher or is “lifting” when the rear end squats down on acceleration.

The 2018-19’s, Ford downsloped the entire front end from the inner fender rails, the front core support and outer sheet metal (hood/fenders). The redesign remedied the excessive hood flutter (none at all) and when a 2018/19 accelerates, even with hard launches or at excessive speed the front end is more planted not only physically but from an aesthetics point of view from the driver seat.

You can do as others have said by using aftermarket suspension components to bring down the center of gravity or to improve overall handling - but the high or floaty front end may remain due to how the 2015-17 was designed and how the hood is interacting with wind shear.

The 2015-17 front end looks really long (and high) from the driver seat. I’ve owned a 2016 and coming into the 2018, there are vast differences not only visually but also from a handling perspective. Other earlier posts on this site from owners who have went from an early S550 into a 2018/19 have also posted similar experiences regarding overall STOCK handling characteristics and the view from the driver seat. Of course anyone who has not owned any S550 prior to 2018 will always think the stock suspension still needs improvements.

Not discounting any suspension characteristics that you’re actually feeling, but that 2015-17 high hood line adds to the floaty feeling - because even with a great suspension, the hood looks so long even when going into curves, it appears the front of the car is still plowing into or not following the curve... LOL.

With my suspension the car is rock solid at 145+ mph. No drama. Planted and stable.

 

[motorjock205]

Seeing you have a 2016 based on your profile, in the event you don’t know this small fact - the front ends of the 2015-2017’s will seem “floaty” more so because of the design of the front sheet metal, particularly the hood.

At the speed you were driving on a public roadway (*be careful doing that on public roads....) - you should have noticed considerable hood lift and flutter.

The 2015-2017’s suffer from hood flutter even at sustained speeds of 65-75mph. Due to the overall design of the 2015-2017 front end, it appears from the driver perspective as if the front is higher or is “lifting” when the rear end squats down on acceleration.

The 2018-19’s, Ford downsloped the entire front end from the inner fender rails, the front core support and outer sheet metal (hood/fenders). The redesign remedied the excessive hood flutter (none at all) and when a 2018/19 accelerates, even with hard launches or at excessive speed the front end is more planted not only physically but from an aesthetics point of view from the driver seat.

You can do as others have said by using aftermarket suspension components to bring down the center of gravity or to improve overall handling - but the high or floaty front end may remain due to how the 2015-17 was designed and how the hood is interacting with wind shear.

The 2015-17 front end looks really long (and high) from the driver seat. I’ve owned a 2016 and coming into the 2018, there are vast differences not only visually but also from a handling perspective. Other earlier posts on this site from owners who have went from an early S550 into a 2018/19 have also posted similar experiences regarding overall STOCK handling characteristics and the view from the driver seat. Of course anyone who has not owned any S550 prior to 2018 will always think the stock suspension still needs improvements.

Not discounting any suspension characteristics that you’re actually feeling, but that 2015-17 high hood line adds to the floaty feeling - because even with a great suspension, the hood looks so long even when going into curves, it appears the front of the car is still plowing into or not following the curve... LOL.

I really did not notice the hood fluttering at all, it just seemed like the front end of the car was higher than it should have been at that speed. Yes, I know speeding like that is not appropriate on a public highway...(retired LEO), but I was on the service road of a highway all by my lonesome, so I decided to open it up and see just what it was capable of...and no, I do not have a get out of jail free card because of being retired LEO...The car was pulling hard all the way through the run, just never seemed to settle the front end down...perhaps the styling that you speak of is responsible for that, something to consider anyway. Thanks for the input.

 

[NoVaGT]

Thanks for the reply BmacIL, I don't think I will be lowering it any, I'm 6'3 on top of being 61 years old, and have a hard enough time getting in and out as it is...LOL

1. Lowering the car is like about 1"-1.5", it won't make any difference in getting in and out of the car, it won't make it Ferrari or Corvette low, but it will make a big difference in handling.

Look at this package; https://www.americanmuscle.com/koni-sport-adj-shock-strut-prokit-1516gt.html The shocks, struts and (slight) lowering springs will really help.

Then consider other IRS pieces for the rear of the car. What you do in the rear suspension (cradle and diff bushings, horizontal links, etc.) will also aid in the front end of the car. That might sound weird, but stiffening the back of the car will aid in front end grip and stability.

Also consider a bump-steer kit for the front end, it's cheap and easy.

Then a front splitter, one that actually works.

But, really, stop being silly about this high-speed stability crap. You're 61 years old, and should know better. You'll probably never do 150MPH again in that car again. And your wife damn sure doesn't drive that way.

 

[Triton54]

I can agree with Cobra Jet, since the wife has a 17 PP, and my base 18 auto, i have had them both to 150+ ( just a few seconds really, cause u run out of room so fast) If the road is smooth no problem, back to back, the 15-17 cars hoods are quite a bit higher, than the 18's. My 18 is a bit more floaty though, if the road is NOT smooth, but not enough to abort the run, ( if its clear) and of course those PP brakes on the wifes car, WOW! Both cars totally stock.......

 

[BMR Tech]

The chassis is like a seesaw. The rear of the S550 squats, and when it does the front rises.

The quickest and best way to get rid of the feeling you mention is to limit how much the rear squats, or to drop the front of the car.

A set of lowering springs that has more front drop than rear, with a linear spring rate that is stiffer than stock, is a good idea based on my experience and perception of your post.

 

[Norm Peterson]

OK, I am 61 years old and new to the IRS in the 15-18 Mustangs, but after doing a few updates on the wife's car this past weekend and taking the car out for a test drive, I am wondering how to keep the front end down at high speeds...I got the car up to about 150 MPH and the front end just felt very light and high up in the air...I know the IRS allows these things to squat more in the rear, but at high speed, a light front end kinda makes me nervous...Any help would be appreciated...I know you young guys can steer me straight on this. I will add that we just put new Cooper RS G3 235 18 tires on the car and I also replaced the brake pads...Car has just shy of 30K miles. I wouldn't think that the struts would be worn enough to let the front end go up so much, as they seem tight when I push on the fenders.

Got to admit I'm a bit uneasy about going that fast in a car that weighs close to two tons (including the necessary driver) on anybody's 235/50 tires or wheels only 8" wide. But I guess that's something for later rather than sooner.

I agree with Bmac that dampers really do have to be your first step from here, and these can add a great deal of composure even if you don't do a spring swap at the same time. I'm going to suggest single-adjustable dampers, as you can dial them in to better fit her preference for most street driving and yours during any higher speed stuff. Maybe find an HPDE event for the 3-digit stuff.

You may also benefit from giving the car a little more roll stiffness.

It's at least possible that the IRS's softer "feel" is changing the perception of how much pitch (nose rise/tail squat) is actually happening, Better damping can make the same amount of pitch less objectionable.


Don't let anybody tell you that you're too old to drive fast, or that marginal high speed stability is something that you have to avoid by always going slow. If I had 150 or so more HP under the hood of my '08 I'd be driving well past the 125-ish that's all she writes on my home tracks (and crowding 150 if I ever get to any of the longer higher speed tracks). Just so you know, I've recently started on my 72nd trip around the sun . . .


Norm

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