Clarification of IRS v. Live

[SurfnSoCal]

Both of my roomates have 97 BMW M3's. They have "Dinan" tuning on them, and are quite quick. Obviously, I can't keep up with them with my current car; but once I get an 05 GT...things should even out a bit. I think stock they sit at 260hp.

They have been giving me crap for buying another car with a live axle. Its the 21st Century...shouldn't I get a car with IRS?

Heres my question:

Will the IRS make THAT much of a difference in handling...and being able to keep up with my M3 friends? I am hoping (and am almost certain) that the new 05's will handle alot better than my current Stand; but will it still fall behind in keeping up with my buddies when we tear up the streets arround our suburban home?

I know its all speculation, but for all of you that have owned IRS (Preferbly German) cars and Live axle equipped cars; what is your opinion?

I am tired of them making jokes at Ford and its Live Axle...and how grat their BMW's are. Screw BMW.

 

[awalbert88]

Well, there's no telling how the new Stang will perform, because there haven't been any tests done independent of Ford. It will definately out-handle the current Mustang. It might actually keep up with an M3 on the track by virtue of having more power, but I think that the M3 will still outhandle it. The '97 M3 came with 240hp and 236ft/lbs stock.

 

[SurfnSoCal]

AH...thanks for the clarification on the stats. I wonder with a good suspension set-up on the 05', if it would hang.

I read somewhere that Ford payed close attention to the 3 series BMW when designing the suspension/handle.

Yeah, I think in any roadrace the M3 will out handle...but I am tempted to think it will be very close...and even closer once MM, Steeda, etc. start coming out with suspension gear for the 05.

I would like 300hp would kill 240hp, even if the stang weighs spprox 300-400 more (?), in any drag race. Its really going to depend on how committed to the 5.5 sec 0-60 time Ford is claiming. Lets hope for a flat 5 maybe.

 

[shatner saves]

This is from a stangnet article on the svt cobra:
"The IRS is beneficial for multiple reasons including a reduction in unsprung weight by 125 pounds, a widened rear track of 1.2 inches, and a .25 inch lower ride. This translates into better road feel and handling because the rear suspension handles road irregularities better, and helps plant the rear end of the car in turns and reduces lift and dive characteristics under hard acceleration and braking."

 

[SurfnSoCal]

Beside reducing weight, becuase more parts = more weight; wouldn't upgraded suspension parts for the Live Axle be able to do the same (reduce lift, plant the rear end, etc.)??

 

[shatner saves]

here is a really good link describing different types of rear suspension:

http://autozine.kyul.net/technical_school/suspension/tech_suspension1.htm

 

[SN95_XB331]

Actually the case maybe reverse, the live axle does very well on a nice smooth track. And with the panhard bar/3 link setup and MUCH better weight distribution, *and* the extra TQ from the V8, the '05's should easily keep up, even outrun the E36's on most tracks. (Now the E46's are another story )

On the streets, i.e. roads (canyon carvers, etc...) with A LOT of irregularities and quick changes in elevation, the IRS will destroy a live axle setup. Plainly the IRS (geometry) adapts much quicker to "sudden changes" in road conditons--Of course, a little extra TQ can help that out

 

[SurfnSoCal]

yey...there is hope!

 

[Z28x]

Live axel is better for drag racing and towing (not that you will do that with a stang), plus it is lighter and less expensive.

IRS generaly offers a smoother ride and is better for road course duty. That doesn't mean live axel can't handle great, Just look at the 1LE Camaros, Mustang Mach 1 even pulls #'s as good as a lot of IRS cars. Just because IRS is a little better at cornering that doesn't make a live axel bad at it.

 

[351CJ]

In a street car the advantage of IRS verses a good live axle is mainly about ride comfort and keeping the car planted over bumps, dips and other irregularities in a corner.

In road racing, where the rules allow IRS, live axle race cars became completely uncompetitive in the early 1960's. That says it all.

 

[shatner saves]

The unsprung weight is an issue. It probably doesn't mean a lot in a skid pad test (smooth surface, constant radius), but it's transitional behavior wouldn't be as good as a car with a good IRS. I would be really interested to see slalom test comparisons between an SVT cobra and a current GT.

One advantage that no one has touched on is reliability. Most Live axle rear assemblies are very robust. The long term mainanence costs are virtually nill compared to IRS.

 

[66Satellite]

but will it still fall behind in keeping up with my buddies when we tear up the streets arround our suburban home?

If you want to race, go to a track. The new Mustang should be able to take the older M3 on the drag strip, but it's hard to say what would happen on a road course--more to do with setup and driver skill.

Seriously, don't drive like a reckless idiot on the street.

 

[65conv50]

If you want to se the difference in IRS and live axle, try them both on a nice curve with a railroad track in the center (as I did a few years ago). IRS will keep you on track, while about any LI will have you sideways.... particularly if you are accelerating.

 

[Z28x]

From autoweek.com

Suspension is MacPherson struts in front and a live axle with coil springs in the rear. Surely there will be many of you decrying Ford’s use of a live rear axle in the 21st century. Consider, though, that Mustang engineers went this route because they claim they can tune the suspension to be better than some independent setups, as well as because an axle gives the Mustang better drag-strip-launch characteristics than does an independent setup. (You must love that last qualifier of pony-car character.) It also helps that a live axle is cheaper, keeping the car’s MSRP down. “We saved $300 a car, and that’s just materials,” Thai-Tang said. “That doesn’t include design, engineering and development, prototyping and tooling.

 

[rhumbline]

In comparing two well designed suspensions, one IRS, the other a live axle, the differences would be thus:

On very smooth roads and surfaces there is probably very little difference, but then again, in such conditions, neither suspension really is doing much anyways (hardly a very discerning test of capabilities). So for such smooth, ideal conditions situations like a drag strip or stoplight racing, even cornering, it would be a wash with perhaps the live axle benefitting on the strip.

However, in less than ideal conditions, the live axles relative capabilities, both ride and handling, quickly deteriorate as compared to an IRS. The live axle's main Achille's heel is it's huge unsprung weight, even if the overall rear suspension weight might be slightly less than an IRS. There is just so much mass and inertia to control when the suspension actually is called on to actively suspend a car rather than passively sit still as on smooth surfaces. In such real world conditions, an IRS thus maintains a far better ability to maintain control and adhesion with the road and gives much superior overall dynamic performance. This will allow both better acceleration, cornering and braking, all at better ride quality levels for a given level of handling dynamic capability.

It very much is about much more than simply a cushy ride as some try to imply, though you do get a superior ride/handling compromise as a bonus, there is serious performance benefits to be garnered.

This all does presume two good designs, live axle and IRS. One can always trot out a particularly bad IRS to compare to a particularly good live axle design to try to give an inaccurate general comparison ("...my daddy's '63 Corvair with IRS had evil handling, so all IRSs suck as far as I'm concerned...").

 

[Predator03]

Selling NEW 03 Cobra IRS

Thats right. I'm selling new 03 Cobra IRS. It has everything and only 3k miles.

Interested: Looking for only 1200.00 maybe 1000.00.
No brakes included.
Serious: Call me at cell 956-342-2900
Email: [email protected]

 

[Ray III]

The reasons for sticking with the traditional live axle have already been touched upon: simpler and more reliable design, harder to break under heavy loads, lighter weight, and cheaper to manufacture a tried and true design. The Mustang is not grandpa's European sports car with all the handling refinements; it is a tough and powerful street cruiser. People these days are getting confused on what a Mustang should deliver. From the start, it was intended to be an inexpensive and reliable ponycar. THAT'S IT. Quit ragging on Ford to spoil a car everyone loves on the grounds that it doesn't keep up on a convoluted roadcourse with a car that was built to handle.

 

[Rootus]

Keep in mind also that the only live axle we have any experience with at this point is the current one. The biggest problem with the setup we have now isn't just that it's live, it's the quadra-bind suspension design. I'm betting that the '05 GT with a live axle will out corner any Fox-based Mustang, including IRS equipped Cobras (stock v. stock). I think most people won't be able to tell that it's got a live axle instead of IRS.

Dave

 

[duner]

The wheel hop on my car is starting to drive me crazy. I doubt Ford will improve the IRS design well enough to solve the hop. I'm beginning to wish the '03 Cobra had a setup like the '05 GT.

 

[BelueLX]

Why did they put it in the Cobras to begin with?