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Thread: IRS vs. 3 link vs. 4 link
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07-22-2020 #1Registered User
- Join Date
- Jul 2020
- Posts
- 29
IRS vs. 3 link vs. 4 link
Hi all... I’m new to the forum, and am looking forward to seeing everyone’s projects.
I have most of the plans worked out for my build and hope to start on it next spring.
The car is a 65 fastback mustang...
I’m staying very focused on the weight of the car, and trying to keep it no heavier than 2600 lbs.
It will be a touring, track car. The wife and I plan on doing road trips to shows, and track events.
Hot Rod power tour and such are the types of things we are looking to do, along with the occasional track day (she’s a bit of a gear head herself... I got lucky).
It’s a dream of mine to drive this car at places like Watkins Glen and the like.
The one thing I am still hung up on is rear suspension... I’ve talked to several builders, and suspension shops, and I get a mixed bag.
On IRS I’m told everything from, “you can’t go wrong with the performance” to “it’s heavy, I can’ build a 4 link that will handle just as well, or better”. The last quote was actually by a guy that built and designed a solid IRS system.
On 3 link... particularly with a torque arm and watts, I’m also warned about weight, and steered towards a 4 link.
So the question is...
From a performance stand point only what do you guys think of the 3 suspension systems?
Keeping money out of it... can a 4 link handle as well as an IRS?
Is the IRS really that much heavier?
Some people swear by a 3 link why?
I plan on trying to drive some cars that are built, but I’m wondering if any of you out there that are running these cars hard can help me on this so I can make up my mind on which way I want to go.
I know this is long, but I like to give all the background info so you know my plans, and my approach.
Thanks for the input.Rick
65 Fastback Mustang
89 Daytona Shelby
18 Charger R/T Superbee
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07-22-2020 #2Registered User- Join Date
- Sep 2007
- Posts
- 424
IRS -
I have often heard "A good solid axle can beat an IRS on the track."
That's sort of like saying "A good carburetor can beat EFI on the dragstrip." It's true but it's not the whole story. That setup only has to be a one-trick-pony.
You need a good suspension design if you are going to make it work. Flex. Travel. I mean while the driver is pushing it hard.
Hypothetical - Take a track car that drives only on very smooth pavement. The body motions are all pinned down. Low ride height and stiff springs/shock/sways, etc.
That suspension isn't moving very much because it's set up like an overgrown go-kart. (At that point it would probably respond to aggressive wheel alignment more than good geometry.) On that car an IRS may not earn enough to offset the weight penalty. But IRS shines in the real world where suspensions have to handle big bumps & potholes at all the wrong times.
Solid axle 3-link vs 4-link -
IMO a 3-link (combined with a panhard/watts) is a superior design in general. The lateral location is controlled separately from the longitudinal motions and you can tune it better. No binding bushings. Etc. The 4-link is popular with OEMs because most buyers won't be wanting to adjust anything and it's perhaps a little bit easier to package.
BTW, if you put much priority on being able to hook the tires in a straight line (drag racing) then this is a no-brainer. Stick with solid axles. IRS is inherently worse for that no matter how much optimizing/tuning it has. Having the differential mounted to the chassis makes it impossible to get the kind of anti-squat geometry that solid axles have.
07-23-2020 #3