cobra irs vs solid axle

[Quicktime_GT]

I think its a lot cheaper to build a straight axle to hold launches on slicks.. but IRS drives like a dream

 

[wheelhopper]

^ You need to check the forum next time. This is the OT forum. Most of people that frequent here, or ask a question like this, could care less about how well the car launches from a dead stop.

But, to entertain your argument anyway, the straight axle would be cheaper to build for drag racing, if that is what your car came with. If not you have to locate all the straight axle components.

 

[TroyV]

I liked my 99GT, but my only criticism about it was the snap oversteer at the limit. It seemed that no matter how I tried to tune with bars/springs/tire pressures, It would stick right to the limit, then just snap out instantly.. The IRS is much more progressive in its release at the limit. With my somewhat less than cat like reflexes, it is much easier to drive my Cobra at the limit than my GT was....for that reason alone.

 

[blainestang]

Copy and Paste from a thread I started on 3.8mustang.com regarding the comparison of IRS to Solid Axle:

I did a lot of looking around for information like this when I was determining what direction I wanted to take for my OT project, and a lot of the information I found was from people who had driven MOSTLY one style of rear suspension, people who had driven both but weren't able to quantify the differences clearly, etc.

The following review from MM's driver Dave Royce, with the addition of the follow-up info from Jack Hidley, is easily the best comparison I've seen of the two setups.

The following, provided to me by Chris Phelps of Maximum Motorsports, is an interview of Dave Royce, driver of the #91 Maximum Motorsports car, following the car's debut American Iron event, which it won.

The #91 car was previously equipped with the full MM front and rear setup including Torque Arm, Panhard bar, coilovers, etc. The solid rear was then replaced with a Cobra IRS with the full catalog of MM bushings, tie rods, bumpsteer kits, etc.

Let me preface this by saying that the following is the OPINION of Dave Royce, who is employed by Maximum Motorsports, the company who's product is being reviewed. Keep in mind also that they are comparing their IRS setup to their own Solid Axle setup, not a competitor's product.

Point being, don't take this simply as gospel because it IS a review of a product by that company's own employee, BUT don't discount it immediately either because it is a comparison of two of their own products.

IRS Questions: Answered by MM test driver Dave Royce.

MM test driver Dave Royce answered these questions after he won the first American Iron event we entered after swapping an IRS into the MM race car.

Dave’s answers may be quoted, or just use them for background information when talking to customers.


Compare driving the car with the IRS to driving it with the Solid Axle with Torque-Arm & Panhard Bar (SATAPB).

1. Were there any differences during corner entry between the SATAPB and the IRS?
A - Corner entry is changed in a way I didn't expect. Like the SATAPB, the car has great initial turn-in. However, once the car is set, it seems more stable from turn-in to mid-corner or Apex. This allowed for harder corner entry and earlier throttle application.

2. How does the IRS compare to the SATAPB during mid-turn, steady-state cornering: In long, sweeping turns? In shorter, tighter turns?
A - Mid corner with the SATAPB is good, but the IRS feels very stable and ultimately allows the driver to use either the throttle, brake or steering wheel to make micro corrections to maintain perfect balance. Long, high-speed turns are always a challenge in a Mustang, and the entry and exit play a huge role in how well the middle of the turn works. However, sticking to the question - Mid-turn is quite good. With the SATAPB, I would have to wait just a little through the middle, and then use the incredible launching capability of the Torque Arm to get great straight-away speed. With the IRS, I was able to apply the throttle just after turn-in and maintain some throttle application throughout the middle of the corner. Specifically speaking about the Talladega/Riverside corner, in the counter-clockwise direction, I could come off Magic Mountain with full throttle, make the right hand turn, stay drivers right, and maintain at least a quarter throttle at turn in. After turn-in, I could start to slowly roll into full throttle all the way to the braking zone for the Bus-Stop turn.

3. At corner exit when can you put the power down? What are the differences between the IRS and the SATAPB?
A - Corner exit changed the most. The SATAPB required a relatively straight car attitude to apply all the power, or risk a sloppy, slower exit. The IRS, with increased mid corner grip, allowed for earlier as well as a consistent throttle application (always desirable). Some corners I would be applying throttle just after turn-in.

4. Compare the two suspension types in transitions- especially quick right-left-right changes such as S-curves or slaloms.
A - The key to a great handling chassis is how it transitions, or handles the weight transfer. The SATAPB would transition well, much better then the OE Mustang suspension, but would have understeer and then oversteer - not much transition between the two, requiring at times, requiring the "Good Driver Award" to keep it out of the dirt. The IRS maintained composure throughout the S's. I was able to run full throttle through the S's, and would often touch the curbs without having to apply corrective inputs.

5. Was there any wheel hop during the standing start?
A - The launch was probably the most surprising to me. I have done zero launches with the IRS, so I was ready for one of two things; either a mild to severe wheel hop, or a hazing of the tires. I was sure it wouldn't just free-spin, as it had decent grip out of the low speed corners, so I put that possibility out of my mind. With this mind-set, I readied the car to launch at about 2500RPM, while rolling on the throttle and letting the clutch out in a rapid, controlled release. Much to my surprise, the car hooked up with absolutely no wheel hop. I believe the tires were hazing, or slightly spinning, but I was able to keep rolling on the throttle until it was time to pull second gear, and so on.

6. Compare the SATAPB and the IRS in how the car reacts to hitting berms, and other variations in the track surface, such as large bumps or dips.
A - I touched on this a couple of questions ago. When hitting "berms" the SATAPB, or more specifically straight axle, as I don't think the TAPB is a major contributor to this change, would usually set the back of the car over or upset the balance to the point where the driver would have to induce correction, obviously slowing the car. The IRS does what you would expect. It leaves the outside tire with full contact, while the inside tire rides over the berm. This was very noticeable in high speed corners where there is a small steep berm that usually must be avoided. I was able to allow the inside rear tire to be on the berms, and not have to lift off the throttle. This provided that extra few inches sometimes needed to keep from sliding off the track at corner exit, as well. On some berms the rear felt a lot like the front, almost a non-issue.

7. Which would you rather drive, a Mustang with IRS, or a Mustang with a solid axle and a torque-arm?
A - IRS, hands down!

8. How was the braking with the IRS, compared to the SATAPB? Was there any rear brake hop?
A - Braking was a little better. The biggest advantage was the ability to do more trail-braking, deeper into the corner No detectable wheel hop under braking was experienced.

9. What were the worst features of the car with the IRS? With the SATAPB?
A - IRS, not enough horsepower. Too much body roll.
A - SATAPB, not enough horsepower. Seemingly difficult to tune in consistent and predictable corner grip. You can tune it for better entrance, better mid-corner, and decent exit grip, but getting all three seems to be a challenge.

10. What were the best features of the car with the IRS? With the SATAPB?
A – IRS, Terrific transition and mid corner grip. Able to roll onto the throttle earlier. The ability to negotiate berms and curbing without upsetting the car.
A – SATAPB, Great acceleration, no wheel hop, substantial improvement over the OE 4-Link.

11. People often complain about wheel hop during acceleration with IRS cars. Was this a problem you saw with the MM race car?
A – With the setup from MM I completely forget that IRS has a wheel-hop issue. In fact I can say there is no longer a need to associate wheel-hop with IRS, at least with the set-up I drove from MM.

12. You have driven the MM race car with both our complete solid axle torque arm system, and our complete IRS system. What would you say to people that are considering either switching to the IRS or to a solid axle, in cars that came with the opposite rear suspension? Assume they were looking at it from a performance standpoint, were technically able to do the work or have it done, and wanted to make their car handle the best they could? Is there a clear winner between the two?
A – The SATAPB is a lot better the OE, but requires the driver to mechanically balance the car during corner exits. The IRS has a more natural balance tendency, and therefore is easier to keep balanced on the edge with the throttle and brake. So the clear winner is the IRS.

13. How would you compare the modified IRS in the MM race car to other IRS-equipped cars you have driven on the track?
A – I would say it’s comparable to any IRS car I’ve driven. It’s better than most stock IRS, including the Cobra.

14. How did the entire MM road race car, in its current IRS form, compare to other road race cars you have driven?
A – The MM road race Mustang was comparable to the GT3 Porsche in a lot of ways. This may be due to the fact that I set cars up similar for my driving style, but it usually is the fast way around the track. The high-speed stability is good, trail braking is much improved, and steering response at turn-in is great.

15. Did the MM products on our IRS cure any issues or complaints you observed when testing any other IRS-equipped cars?
A – Some IRS cars do not allow for enough camber adjustment, and have undesirable bump-steer.

Did the MM products on our IRS cure any issues or complaints you observed when testing any other IRS-equipped Mustangs? (i.e.: Did you notice any benefits from the MM IRS products we added to the OEM Ford IRS?)
A - As compared to the stock Cobra – street set up – it’s night and day. The OEM car seemed to float around in the middle of the corner, and exhibited unpredictable traction or wheel spin. The MM race car, even with “R” compound tires, felt positive in most driving situations. Mid-corner predictability seemed vastly improved.


16. How is the overall balance of the car with the IRS, compared to the SATAPB?
A – The SATAPB had good balance as compared to OE 4-link and the OE Cobra. After two days of testing the IRS with MM upgrades, I think there is no going back. The balance is what one would expect from a well-sorted performance car.

17. Are there any differences in the tune-ability of the two systems?
A – The ability to tune the rear alignment and static camber is substantially beneficial. If we can get the car to launch off the corner as good as the SATAPB does, you definitely have a better package. However, if I was drag racing, I think I might stay with the SATAPB.

An important update to the above info...

Here is Jack Hidley's (Maximum Motorsports employee who is active on the Corral and corner-carvers, etc) response to my posting this interview on the Corral...

EDIT: Link to source (See post #40 for the interview and my question for Jack, and see #44 for Jack's response) : http://forums.corral.net/forums/showthread.php?t=1035954

The IRS was about 2 seconds per lap faster at Buttonwillow than the TAPB in our #91 car. The lap times are around 2 minutes and the car has about 315rwhp.

Having driven the same car both before and after the swap, I agree with Dave's comments. The IRS makes a much nicer handling car, that is much better over bumps, in braking and has a more consistent balance during all phases of cornering. It isn't necessarily going to be the fastest on all cars at all tracks. The TAPB can put down quite a bit more power on corner exit. In a car with a lot of power, this is going to be a big advantage over the IRS.

The IRS is more expensive the purchase, modify, install and maintain. You have to now deal with 4 wheel alignments.

 

[ac427cobra]

As I've said many times before, the SRA is very easy to understand. The IRS is quite a bit more complex.

It's a shame the IRS was so compromised as delivered from the factory. There is a lot of dislike for the IRS and I honestly can't say it's unwarranted.

I try to get the idea across to people that the IRS is a superior suspension component but there is an awful lot of resistance 'out there'. Many people think the answer to their problems is putting a stick axle into their Cobra. :rollseyes

But as evidenced by the testimonies above, IRS>SRA hands down.

:thumbsup::coolman::beer:

 

[gcassidy]

Thanks for posting, Blaine. Like EF Hutton, those are 2 people that when they talk, I listen.

I suppose I'm lucky that I don't have the funds (or probably the expertise) to swap out my stick. I don't have to agonize over the choice.
But I find it interesting that the HP of their test car is the same as my car, so my results could be expected to closely resemble theirs. Not that I could feel the subtleties like they can.

 

[gcassidy]

As I've said many times before, the SRA is very easy to understand. The IRS is quite a bit more complex.

It's a shame the IRS was so compromised as delivered from the factory. There is a lot of dislike for the IRS and I honestly can't say it's unwarranted.

I try to get the idea across to people that the IRS is a superior suspension component but there is an awful lot of resistance 'out there'. Many people think the answer to their problems is putting a stick axle into their Cobra. :rollseyes

But as evidenced by the testimonies above, IRS>SRA hands down.

:thumbsup::coolman::beer:

Bruce, when youz right, youz right. :rockon:

 

[blainestang]

Thanks for posting, Blaine. Like EF Hutton, those are 2 people that when they talk, I listen.

You're welcome, and I agree... I've seen a lot of "I think this is better" and "I've driven both of them on the street once" and stuff like that, but there aren't many people in the world who have the kind of experience that Dave Royce has, having driven the exact same car with a well-built version of each suspension underneath.

 

[RedTwilight]

Too bad the tubular sub frame from D'agostino Racing didn't pan out!
http://www.modularfords.com/forums/showthread.php?t=115023&highlight=install+IRS&page=12
It would have been a great opportunity lower the compromise in the OEM IRS. It could have been a little lighter. Bringing it closer to the the weight of the straight axle with a TA and PB added. It could have also been a great chance to improve the geometry of the OEM design. Then all the neighsayers would have less excuses.

I have an '03 IRS sitting at home waiting for some mods before it goes into my '96. First thing will be Bruce's Bushing kit and a Fore diff cover.

 

[wheelhopper]

I have 1 complete IRS assembly and another cradle and A arms that I have talked with a fabricator about doing this exact thing. Making the rear cradle assembly from chromoly and making whatever changes to improve upon the current design. I will probably just get the A arms done, for now. But eventually I will do the cradle. When I get these items fabbed up I'll post it.

 

[Sintore]

To be fair you would need to add in the cost of a new IRS; you may already have it but I don't believe the OP does.

For those of us with '05 and up S197's, we don't have a factory IRS option, we have to work with what Ford gave us. There are a couple of aftermarket IRS options for the S197 that I've researched, but IMO they are not will suited for high HP, road racing use.

OP, this is a very good read on your topic, you may want to check it out TheMustangNews.com - Does The Mustang Need IRS?

Good reading...

John