Your thoughts on IRS

[Balr14]

I have owned an older solid axle Mustang, but that isn't a valid comparison to a modern Mustang, as there is a whole lot more than the rear suspension that's different.

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[AfricanSnowOwl]

I've owned many mustangs over the years, some stock some highly modified, but my 2020 GT is the first IRS car. Gotta say I love it. That probably wouldn't be the case if I spent a bunch of time at the drag strip like I used to, but I don't. IRS is perfect for my daily driving, occasional highway pulls, and tearing up the lone windy back roads I take at work.

 

[bluebeastsrt]

Just a little history for you about my ridiculous statement. While I'm a long way from being a pro driver I have attended a SCCA driving school and stayed with it up until I couldn't go any further without getting my license. I chose to stop there because I had to weigh the cost of moving forward versus the amount of time I could run the course. No racing, just open lapping days using your own car.

Also my question was to people who had owned other Mustangs with a solid rear axle if they could tell any difference. Only one reply so far says he's had older models and he prefers the solid axle. So thank you for a childish smart ass reply but your opinion is of little value to me.

I've owned 2, 1971 Mach-1's. A 1986 GT. A 1995 GT that made about 800whp. A 2011 GT. A 2011 V6 daily. a 2015 GT that made about 800whp. and finally the current 2019 GT. And I can say with out a single doubt. The IRS equipped Stangs handle MUCH better. I don't know what home boy was talking about as far as "not a fan of the IRS when it comes to walking the rear out". Who drives like that? But I can say the IRS won't tram-line or hit an imperfection in a curve and jump out of it's corning line. like the solid axle cars have all done that I've owned. If you're a dedicated drag racer. Solid rears are better. But that will be the only duty where the stick rear will out perform an IRS. Ford said the 15 GT would outhandle a Boss 302. And the boss 302 was supposed to be the pinnacle of the stick axle as far as handling was concerned in Mustangs.

 

[EcoVert]

I have driven a lot of Mustangs over the years and the 15 and up Mustangs with IRS have them all beat in the handlining department.

 

[bluebeastsrt]

I’m with the OP on this. I’ve driven/owned many mustangs (1960’s, 70’s, 80’s, 90’s, 00’s and up to current models) and I honestly prefer the solid axle. It feels lively, compared to the IRS that is just numb and boring. While I don’t agree with all the criticisms that solid axles get, I can understand where people are coming from. Solid axle still wins for me though.

That lively feeling you're experiencing is the car moving around. I think people are confusing planted with numb & boring. I don't want to go into a corner and have to worry about the car completely jumping off it's line because of a ruff patch of pavement. As lively as some would call that. It just makes me pucker! That's what the stick rears would do. It's old technology. Not better technology. There's a reason the entire automotive industry went away from it in sports cars.

 

[AceS550]

That lively feeling you're experiencing is the car moving around. I think people are confusing planted with numb & boring. I don't want to go into a corner and have to worry about the car completely jumping off it's line because of a ruff patch of pavement. As lively as some would call that. It just makes me pucker! That's what the stick rears would do. It's old technology. Not better technology. There's a reason the entire automotive industry went away from it in sports cars.

All valid points. IRS outperforms solid axles in cornering ability. Solid axles outperform IRS in drag racing. I just wish there were more twisty roads around me to enjoy the IRS.

 

[Rapid Red]

I was thrilled to learn the Mustang came with IRS, when ordering.

Curious "Solid axles outperform IRS in drag racing" how so? Other then axle failures, not that. that is a good thing.

 

[Hack]

I owned two different 2011 Mustangs. One was a V6 car and the other was a GT with the Brembo brake package, which was a precursor to the Track Pack. So, it had the stiffer springs and upgraded shocks to go with the Brembos. Then I owned a 2015 base, then a 2016 GT350 and now I own a 2017 PP1 GT, which I've upgraded to the track handling package. So I think I have a decent background of experience with the better stick axle cars (but not the Boss 302 best one) as well as the IRS cars.

What I found is similar to what some others said previously. The stick axle cars handle great on smooth surfaces and in a straight line. A SRA is great for putting power down in a straight line. But I found body control to be poor when the suspension was soft, and with stiffer suspension the car could really jump around if there were imperfections in the road. Also, the stiffer suspension meant for good handling felt like it was shaking you on regular freeway expansion joints. So much so that I actually felt I almost lost control of my 2011 GT just driving down the freeway when I hit a larger imperfection in the road.

For the IRS, I think Ford made the base cars almost too soft. But the IRS gives much better grip on real roads (not a straight line 1/4 mile track) with imperfections and curves. And when equipped with the performance versions of the suspension with IRS, the car is outstanding. Not too stiff and with great body control and amazing grip of the road.

Prior to 2015, I really didn't want the IRS because I knew the price of the car would go up a few thousand dollars. However, after driving the newer Mustangs I think they are much, much better with IRS. I can definitely understand if you live in an area with really good roads and you are a quarter mile or straight line person you might prefer the solid rear axle, though.

 

[Norm Peterson]

Curious "Solid axles outperform IRS in drag racing" how so?

It's much easier to build more anti-squat into either 3-link or triangulated 4-link stick axle suspensions than into most any IRS (S550's integral link included). That goes to initial launch bite and short times.


Norm

 

[Rapid Red]

It's much easier to build more anti-squat into either 3-link or triangulated 4-link stick axle suspensions than into most any IRS (S550's integral link included). That goes to initial launch bite and short times.


Norm

Cannot argue that, gear sets are better. The 9''design and the ability to change the carrier is another big plus.

Pep

 

[RazzaRossa]

Stick axels can run the gambit too. A stock 1989 8.8" posi can handle only so much before your blowing out axels at the drag strip. My '67 with 9" modular center section and 31 spline axels could handle WAY more HP than what I threw at it, all day long. Just throw money at it, if you beef up the new IRS, It'll perform on the drag strip too, but when it breaks, get out your wallet.
I like the new IRS, but my driving habits nowadays is a bit more tame.

 

[RazzaRossa]

Whoa!!! Internet Bada$$ alert!

 

[Hack]

What do you mean "IRS rolls"? Can you describe this in a more physical, real-world way? I'm sure you don't mean the IRS rolls, but I really have no idea what you actually mean.

Are you talking about roll stiffness like how well the car's body rolling is managed under cornering loads?

 

[WildHorse]

I remember all the S197 guys proclaiming the IRS is garbage for drag racing. Now those IRS cars are running 7's on a stock super 8.8, whereas the s197 guys need serious upgrades to the diff to run the same.

 

[Norm Peterson]

What do you mean "IRS rolls"? Can you describe this in a more physical, real-world way? I'm sure you don't mean the IRS rolls, but I really have no idea what you actually mean.

For any given amount of wheel rate (springs) and sta-bar stiffnesses, IRS cars generally do roll a bit further at any given cornering g level. Has to, since the IRS's geometric roll center is located several inches below production stick-axle geo roll centers. This also helps make the IRS car "feel" softer.

There's somewhat more going on as well. Like how much the suspension stiffnesses affect the progression of understeer while roll is in the process of developing. Cars with higher rear geo-RC heights initially start out being slightly "looser", with the forward bias of roll stiffness dragging that in the understeerish direction as roll develops. More than you'd set up an IRS car to do. What happens between the initial steering and the final attitude of the car in roll matters - transient handling is by nature dynamic and (hopefully) brief, but it's something that you absolutely should be feeling/sensing from the driver's seat.


Norm

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