Is swapping to an IRS worth it?
03-28-2012, 06:00 PM
#21
My buddy just swapped an IRS into his Mach, and I was amazed at the difference it made in his car for DD. There are some pretty iffy roads around here, and it rode much better than my GT with the SRA.
If I could get one cheap with the exhaust (or a swap with someone who wanted a SRA), I would do it in a heartbeat.
If I could get one cheap with the exhaust (or a swap with someone who wanted a SRA), I would do it in a heartbeat.
03-28-2012, 10:48 PM
#23
3rd Gear Member
Join Date: Mar 2010
Location: California
Posts: 611
Your right about not having the tires stay flat. If setup properly, it increases camber when compressed and decreases camberopened up. Meaning better handling through turns. As for the dragstrip, the only reason it does not do well is because of the stock rubber bushings causing wheel hop. Which is fixed by putting in solid bushings. Which not only improves handling, launch control,completely removes wheel hop, it further improves the ride of your car. I like to have my cake and eat it too.
Hmmm. Awkward. I disagree with your statements in bold.
With a solid axle (NOT IRS) the tires are always flat. With an IRS, the rears generally have a little bit of negative camber.
And my justification for NEVER considering a swap to IRS (I have IRS swapped a customer's car though) is that the solid axle is better on the dragstrip and at least as good on a roadcourse. Sure, IRS is smoother over bumps, but if I wanted a car that was smooth over bumps, I wouldn't have bought a Mustang. It's irrefutable that the SRAs are faster on the dragstrip, and on the roadrace track, Ford Racing, Roush, Steeda, basically all of the Pro racers are using solid rear axles. (and winning races on them!)
With a solid axle (NOT IRS) the tires are always flat. With an IRS, the rears generally have a little bit of negative camber.
And my justification for NEVER considering a swap to IRS (I have IRS swapped a customer's car though) is that the solid axle is better on the dragstrip and at least as good on a roadcourse. Sure, IRS is smoother over bumps, but if I wanted a car that was smooth over bumps, I wouldn't have bought a Mustang. It's irrefutable that the SRAs are faster on the dragstrip, and on the roadrace track, Ford Racing, Roush, Steeda, basically all of the Pro racers are using solid rear axles. (and winning races on them!)
03-29-2012, 07:10 AM
#24
Retired Moderator
Join Date: Jun 2006
Location: SF Bay Area
Posts: 9,235
School and Sharad answered much of what I was gonna add to the question of post #8. The IRS will ALWAYS "ride better" than an SRA, as the wheels are independent and one side does not upset the other side as easily. We all see this, but must realize that if one builds the car for serious corners, the springs needed will remove vast amounts of this "better ride". The IRS has much less sprung weight, but much MORE weight overall. Once this is taken into consideration, the issues of very common wheel hop come into play.
Jazzers theory on why the IRS wheel hops:
My car runs an SRA, as everyone already knows, but tremendous rear grip (speaking in a lateral sense here) and next to impossible to oversteer my car on dry ground. Now, if I was to add massive amounts of HP/T, it would not have the wheel hop issues soo commonly found in the IRS. Combine these two issues and that the SRA is less complex to address its fundamental flaws (4-link suspension) and steers many away from the IRS from the "extreme end" of the spectrum.
Now, one wants an improved quality of ride and better lateral grip than most of the SRA's out there.... certainly go IRS
You wanna tangle with The Cat on an open-track/AX environment...? You very well may beat me, but you'll have your paws full 
Jazzer
Jazzers theory on why the IRS wheel hops:
The half-shafts are the main issue with the IRS and the flexability of the lower control arms with reguards to wheel hop, IMO. The wheel hop is generated when the IRS LCA's allow the wheel to "creep" forward on a VERY hard dig. I can only guess how much they move, maybe 1/2" and totally guessing here, but am sure they DO move. When this "creep" cannot move forward any farther, it reaches max deflection and breaks traction. As soon as the tire looses its grip and begins to spin, the force against the LCA "moves" the wheel BACK to its original location, but now it is spinning. The LCA quickly flexes, just as it did a split second earlier and allows the "creep" forward again. This lightning quick repetition, I BELIEVE is the cause of the wheel hop, as the tire keeps "jumping" back and forth between these two slightly different positions. This puts MEGA strain on the half-shafts and they can snap under the machine-gun action of movement. This is 100% theory and the first time I have given it voice on the forums, so hopefully someone will chime in and add/subtract from what I think happens to the IRS under a spinning condition
Now, one wants an improved quality of ride and better lateral grip than most of the SRA's out there.... certainly go IRS
You wanna tangle with The Cat on an open-track/AX environment...? You very well may beat me, but you'll have your paws full Jazzer
Last edited by Jazzer The Cat; 03-29-2012 at 07:13 AM.
03-29-2012, 07:46 AM
#25
03-29-2012, 01:31 PM
#26
3rd Gear Member
Join Date: Mar 2010
Location: California
Posts: 611
I agree with you that there is porblems with wheel hop just as there is problems with binding of the suspension on the SRA. Both have their flaws and both can be fixed. However, after these modifications have been done to both, I believe the IRS is more superior. The SRA causes alot of understeer. Also, there is no adjustment of the caster, camber, and toe. Unless you cut the axle tube and set it up in that way. Im guessing you dont have any issues with understeer Jazzer, mainly due to your exspensive front suspension that I would kill for. But, comparing a car with an IRS with the McPherson Strut against a SRA with the front McPherson strut setup, I believe the IRS performs better, because when setup properly, the suspension will add camber at the correct time into a turn, preventing that undesirable understeer that the SRA is known for. Now I know you will destroy me out on the track because of your experience and the griggs front suspension up front, but that is not a very good comparison. As they are basically different cars when it comes to the front end.
03-29-2012, 03:33 PM
#28
SRA mach1s have won autocross & open track championships against IRS cars, as have S197 Mustangs. SRAs dominate drag racing.
I stand by my comment that IRS is only better for ride quality around town.
I'm not hatin' though. We can all be friends!
I stand by my comment that IRS is only better for ride quality around town.
I'm not hatin' though. We can all be friends!
03-29-2012, 09:20 PM
#29
Retired Moderator
Join Date: Jun 2006
Location: SF Bay Area
Posts: 9,235
I agree with you that there is porblems with wheel hop just as there is problems with binding of the suspension on the SRA. Both have their flaws and both can be fixed. However, after these modifications have been done to both, I believe the IRS is more superior. The SRA causes alot of understeer. Also, there is no adjustment of the caster, camber, and toe. Unless you cut the axle tube and set it up in that way. Im guessing you dont have any issues with understeer Jazzer, mainly due to your exspensive front suspension that I would kill for. But, comparing a car with an IRS with the McPherson Strut against a SRA with the front McPherson strut setup, I believe the IRS performs better, because when setup properly, the suspension will add camber at the correct time into a turn, preventing that undesirable understeer that the SRA is known for. Now I know you will destroy me out on the track because of your experience and the griggs front suspension up front, but that is not a very good comparison. As they are basically different cars when it comes to the front end.
Put it this way... John Griggs, co-owner Griggs Racing and owner of one bad-azz Termi... has an SRA swap!
Jazzer
03-30-2012, 01:41 PM
#30
just stumbled on this on The Corral $350 is a pretty good deal with brakes
http://forums.corral.net/forums/susp...fs-99-irs.html
http://forums.corral.net/forums/susp...fs-99-irs.html