Wheel hop, IRS subframe movement under acceleration, engineering reason?

[sakman84]

I'm hoping someone with more knowledge than I on the subject can enlighten me. I have spent the last few hours down the rabbit hole on S550 wheel hop and IRS subframe movement. Now I typically don't launch the car out of first gear, but I will do a track day or two per year, and canyon carve in between. I have felt wheel hop under hard acceleration, especially on a crappy surface. But for me its not particularly bothersome. I will say the Mach 1 has far superior rear end feel than other S550s, even PP1 I drove. So I know what wheel hop us, and what it feels like inside the car. Watching some videos of wheel hop and IRS movement in action, was surprising to me, like damn that is a lot of movement, maybe I should address this, if nothing else for parts preservation and consistent feeling in the rear.

Ford had to have know this would happen, so my question is, do all IRS subframes move on all cars? And if so what is the engineering reason behind this? Obviously with suspension we have forces and loads being applied in different directions on different parts all constantly changing depending on road surface and driving maneuvers. So I would guess that some movement is not only expected, but likely desired to a certain extent......but this much really???

I started out just wanting to get a stiffer rear sway bar to increase oversteer for track days. I would like to get a bit more rotation through corners, sharper turn in, and more steering response. Now I'm thinking I will get a sway bar, and BMR CB005 "cradle lockout" kit. I did a lot of searching at it looks like many people are pleased with this and it results in a perceived 80% -90% reduction in hop.

Wheel hop and IRS subframe movement, video and one solution. Start video at 1:29.

https://www.bmrsuspension.com/?page=products&productid=1543


BTW my tires are wearing evenly, but I never measured the factory alignment, and the car tracks very straight and true hands off. To improve the steering response I will be adding some front negative camber. Alignment specs are below for reference. Probably going to shoot for -1.26 on the fronts. I will shoot for 0 toe.

Lastly I might add a Steeda 2 or 4 point G Track brace . I haven;t made up my mind on this part.
https://www.steeda.com/steeda-555-5536-mustang-extreme-g-trac-k-member-brace
https://www.steeda.com/steeda-555-5535-mustang-ultralite-2-point-g-trac-brace

Sway bars
https://www.steeda.com/steeda-mustang-rear-sway-bar-2015-555-1016.html?setCurrencyId=1&sku=555 1016&gad_source=1&gclid=EAIaIQobChMIj8b168-8iQMVszHUAR3kYwJsEAQYASABEgL7wvD_BwE

https://whitelineperformance.com/pr...MI0-zA_c-8iQMV8znUAR2C8g2HEAQYASABEgKRDvD_BwE




Bunch of other threads mention BMR CB005 kit or steeda stop the hop kits.
https://www.mustang6g.com/forums/threads/steeda-mach1-suspension-mods.169126/page-2#post-3437544

https://www.mustang6g.com/forums/th...our-mach-1-today.171200/page-366#post-3930291

https://www.mustang6g.com/forums/th...ed-stop-the-hop-packages.189358/#post-3803052

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[Oakley]

here's what made the difference in my car:

1. IRS bushing collars
2. Steeda adjustable rear shocks
3. ford racing toe bearings
4. REAR ONLY poly bushing inserts with big bertha bolt kit (zero NVH increase at speed)

 

[K4fxd]

I'll admit to skimming your post. I think you are asking why Ford made the rear so loose? Most buyers are after a smooth ride above all else and Ford caters to these people. I have no idea why (bean counters most likely) Ford does not use stiffer bushings or bearings in the upgraded performance cars. IE Mach one, GT350 GT500 Bullitt ECT

Just like the TC on an F150 is over intrusive. I had one Ford engineer tell me it was to keep soccer moms from spinning out with kids in the truck.

They want the smooth ride to keep the women happy.

Aftermarket keeps the enthusiast happy.

 

[John Papageorgiou]

-CB005 cradle lockout plus steeda alignment sleeves.
-BMR vertical links
-Ford Performance toe knuckle
-BMR adj toe rods
-BMR LCA spherical bearing (this for me was the surprise packet a little more NVH but stopped wheel hop 100%).

 

[ice445]

I'll admit to skimming your post. I think you are asking why Ford made the rear so loose? Most buyers are after a smooth ride above all else and Ford caters to these people. I have no idea why (bean counters most likely) Ford does not use stiffer bushings or bearings in the upgraded performance cars. IE Mach one, GT350 GT500 Bullitt ECT

Just like the TC on an F150 is over intrusive. I had one Ford engineer tell me it was to keep soccer moms from spinning out with kids in the truck.

They want the smooth ride to keep the women happy.

Aftermarket keeps the enthusiast happy.

I'm fairly sure the GT350 subframe is different with rubber bushings with less of a void than the stock cars that likely hold up a lot better. The Mach 1 should also have this same subframe.

Not responding to you specifically, but IMO a bigger issue with the S550 rear cradle isn't so much the design but the manufacturing variance. If your subframe(s) were installed with poor alignment, it exacerbates all the softness and movement to a huge degree because then it becomes inconsistent depending on what the car is doing at that time. I've seen alignment issues on here from it, with one side having different camber or something else that can't be corrected out by a shop because the subframe has to be moved over. Steeda sells their alignment kit for a good reason I'm sure.

On the other hand, if your car has good alignment out of the gate then I really don't think the rear end is that bad stock. I can feel that the rear end has to catch up with the front on turn in, especially when you have front tires with a lot of grip, but once it does I never found it to be obtrusively bad besides that delay. My car has never once wheel hopped either, but that may just be from living at altitude and making less power.

 

[NGOT8R]

Here‘s a really good look at what goes on with the rear suspension,

 

[paulm1]

mustang rear wheel hop is not just an s550 thing. My '69 fastback had it, my '87 foxbody had it, my '06 s197 had it too.

 

[GJarrett]

Here‘s a really good look at what goes on with the rear suspension,

I have a 3.55 Torsen I am going to install this winter, this looks like an obvious easy item to include when I do it.

 

[MACHtobers Very Own]

I think there's a plethora of reasons. Some make sense some don't. These are just my lonely thoughts as I sip coffee on my porch with dog.

A wise man told me once that in business EVERYONE moves in their own self interest.

Multiple things:

profits
-companies like to make money and cheaper parts and components that don't break when doing basic driving are in favor

Price/market points to hit
-yeah ford could do everything to your car that the aftermarket does from factory. Then you would be in Porsche territory of doing it all from factory the right way. But that's not what a Mustang is for and its brand ethos. Every single Mustang starts out as a eco boost rental car and goes up from there till it reaches the ceiling of where they should land.

Car companies aren't stupid. Engineers know what's going on and ultimately how to fix it but if you want perfection? Gotta pay to play.

Relationship with the aftermarket
-I had a car marketing person tell me that the relationship with aftermarket is tricky but is definately something that's thought about and is worked into engineering. Sometimes yes and sometimes no (tuning ecu for example) there has to be some sort of profit or market advantage to leaving room on the table for aftermarket but this may require more homework.

Market acceptance
Why go cheap? why under engineer for a price point? Because they can. People keep buying the cars. Profit. Self interest. The moment it creates a dip in sales it will be addressed. The amount of people who complain about the irs and drop thousands on steeda's full catalogue while their wife complains about house items needing repair (self shame fills me as I stare into the mirror with "I'm the problem it's me" on repeat) are a drop in the bucket compared to the regular people driving their mustangs and enjoying them.

Parts on my car cause that wobbly rear end scared the shit out of me one day.

2 point G-Trac Brace
Jacking rails
IRS subframe supports
IRS Subframe bushing support
IRS subframe alignment
Aluminum vertical links
Adjustable rear toe links

getting done in two weeks
sway bars
Engine mounts
Camber plates
Differential bushings
Bump steer kit

 

[ing3nious]

Granted I have a PP2 but the following mods made all the difference for tightening up the car across the board:

Stop the Hop Starter Kit 2015+
Extreme G-Trac K-Member Brace

 

[K4fxd]

I can feel that the rear end has to catch up with the front on turn in, especially when you have front tires with a lot of grip, but once it does I never found it to be obtrusively bad besides that delay.

I test drove a 24, I know I know, anyway the rear in it is just as bad as the S550. Get on an on ramp with a constant radius and long enough to get some speed. The rear will not take a set. It oscillates.

Here again "most" people will never go this fast in a curve so the design parameter does not account for this. On a decreasing radius curve it took .8 g on my meter to get the stock rear to take a set.

I thank Steeda for the stop the hop kit because this solved the problem. They named it wrong because it does much more than stop wheel hop. Now if they could only FIX the COATING process. @tj@steeda

 

[MACHtobers Very Own]

I test drove a 24, I know I know, anyway the rear in it is just as bad as the S550. Get on an on ramp with a constant radius and long enough to get some speed. The rear will not take a set. It oscillates.

Here again "most" people will never go this fast in a curve so the design parameter does not account for this. On a decreasing radius curve it took .8 g on my meter to get the stock rear to take a set.

I thank Steeda for the stop the hop kit because this solved the problem. They named it wrong because it does much more than stop wheel hop. Now if they could only FIX the COATING process. @tj@steeda

OSCILLATES!! That's the word to describe!!!

I kept using "wobble" but always knew there was a better word for it!

 

[Noleftist]

This is what I had installed on my daily driver and Road track Mach one with the handling package. I did not want to lower it or make it a bad daily driver but at the same time I wanted something that would make it a little bit better handling. It seems to have really improved handling and TRACTION. Good luck.

Qty.​ B/O​ Shipped​ Item #​ Description​ Unit Price​ Disc​ Extension​ 1​ 0​ 0​ BMR-CB005H Cradle bushing lockout kit, level 2 199.9500​ --​ 199.95​ 2015-2024 Mustang 1​ 0​ 0​ BMR-CB762H IRS subframe support brace 239.9500​ --​ 239.95​ 2015-2023 Mustang 1​ 0​ 0​ BMR-TCA048H Vertical link, rear lower control arms, poly bushings 89.9500​ --​ 89.95​ 2015-2023 Mustang 1​ 0​ 0​ BMR-TR005H Toe rods, rear, double adjustable, rod ends 219.9500​ --​ 219.95​ 2015-2023 Mustang

MERCHANDISE INVOICE TOTAL $ 749.80 INVOICE TOTAL $ 749.80 CR. CARD: AE, APPR:220345 $ -749.80 BALANCE FOR THIS ORDER $ 0.00​ ​

 

[Bman5150]

Great thread. “Oscillation” is a good way to describe the rear suspension compliance. The phrase “wont take a set” also is accurate.

the one performance related thing I do not like about my Mustang is the rear suspension compliance. There are two driving scenarios that give me a serious “oh sh$t” moments thanks to the stock rear suspension:

1.) quick, aggressive left to right transitions (causes the major rubber band effect and easily disrupts the chassis)

2.) higher-speed aggressive turns. As mentioned, it’s difficult to get the suspension to take a consistent set so you feel like you need to make micro steering adjustments to counter the this and it’s not normal understeer/oversteer stuff. It’s spooky stuff happening to the rear suspension geometry that isn’t confidence inspiring whatsoever.

I don’t really feel like modifying this Mustang very much, but I would like to address this issue. I’m starting with the cheapest, easiest route-I’m going to install Steeda’s IRS braces and see what that gets me. I suspect it will get me to “satisfactory” but we’ll see.

 

[K4fxd]

I’m starting with the cheapest, easiest route-I’m going to install Steeda’s IRS braces and see what that gets me. I suspect it will get me to “satisfactory” but we’ll see.

I did the stop the hop kit one piece at a time and the first thing I installed were the braces. They take care of about 90% of the issues. The other 10% bugged me so I added the rest, like I said one at a time.

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