andrewmp6, I am going to have to disagree with you. I am sure we will have to agree to disagree on this one, but I could not let the downplaying of IRS go unanswered Yes a 3 link or 4 link will out handle a STOCK IRS unit, which most are, or a variation there of, but if you compare a performance IRS unit, one with adequate vertical travel stabilization including but not limited to dual coil over shocks, solid trailing arms, and a good sway bar the upgraded unit will out handle any link system any day of the week. It is kind of like comparing two motors that are side by side the first is a performance 302 and the second is a stock 351. With the right performance build the 302 could out perform a stock 351 in every aspect, just as a 3 or 4 link rear axle (the whole thing is a performance upgrade) will out perform a stock IRS unit. BUT if you make the same type of performance upgrades to the 351 that were made to the 302 than that 302 will not stand a chance. I mean lets look at this logically if a 3 link or 4 link was better don't you think the front suspension would get tied back together and not be independent?? Even more so why have trucks gone from solid front ends to independent?? As far as "ask any real road racer none of them use a IRS" the reason is not that a 3 or 4 link provides vastly better handling but rather handling that is almost as good as the IRS counterpart with far less complication, maintenance, and expense. Your argument is kind of like comparing organic produce to regular produce and saying regular is better because all the stores carry it, and in larger quantities. When in fact the quality has nothing to do with why the stores care it disproportionately. It has to do with ease to produce and maintain, cost, and the fact the one is almost as good as the other. Even your own articles talk about the virtue of IRS. lets look at it from another point of view, most sports cars have come with IRS. Especially those designed to go 200 + MPH on the Audubon where suspension must perform well. If the 3 or 4 link was better then it would have been the rear end of choice on all these sports cars. Lastly you have said that IRS wins for ride quality, well less than 5% of mustang builders are building their cars for the track I would guess less than 1% so for street cars wouldn’t ride quality be #1 goal especially when you get better handling to boot I simply do not understand why some people are against IRS. I will concede that is sucks for hard launches, but other than that it is a proven superior rear suspension system.

 

It comes down to what you want to do and the money you have to spend. 3 link kits for the Classic Mustangs are not cheap, and if you can fabricate, then you could put a factory IRS conversion in for less money(like the Jag setup). Both 3 links and IRS can be made to handle VERY well, often beyond the capability of most street tires. IRS rides better and 3 link launches harder. Ultimately though, the suspension, whatever it is, needs to be set up right.

 

Amen!!!!!! That is the main truth to suspension and almost everything car related, you can throw parts at the car but if they are not the correct parts and more importantly the correct pieces of the system than it will never work at optimum performance. I am working on new web page going through all the details of front and rear suspension and the most important part is making sure it all works together.

 

Your forgeting about one kinda car a nascar they can do 200mph+ and handle and they use a straight axle with trailing arms same set up 60s chevy trucks used.The reason i don't like a irs is i had a miata and 240sx both irs both i broke or got left in the twisties here by my friends fox body and don't get me started on wheel hop and body roll.

 

ummmmmm there are no bumps in nascar, if all you are doing is cornering and going starate on pristeen pavement why not use a live axle there is no need for IRS, plus as you said wheel hop, as I have said before IRS has one major pit fall and that is hooking up when launching so yes nascar makes more sense to use a live axle. If I were you I would take a ride in a Mustang Cobra with IRS, a corvette or a Jaguar, and then decide. Of course you don't like IRS if your history with it is a Miata. Thats like deciding you didn't like Fords because you once had a Fiesta

 

so from a more performance street use im assuming the IRS would be a better investment? i wouldnt mind being able to really throw the car around the turns. so with a steering rebuild and new suspension would i be better off getting a new IRS rear end, or building a three or four link?

 

my vote is for the IRS, but I bet you figured that

 

I have drove a 03 cobra and many corvettes still don't like a irs the problem i had with the miata was the 351w i had shoe horned in it i broke a lot of things even had to upgrade to the rx7 irs to handle the power.Not every race track is prefectly smooth and nascar and indy do race at the same tracks.

 

The GTV I had, back in OZ, would out handle virtually all other cars on the road.
Even the cops could not keep up in the twisty section, and yes they did try and
I was not trying so hard to keep them behind me. Personally, I cannot see any
solid rear axle street car getting anywhere near that level of performance on twisty
bumpy roads. As for NASCAR, outside the US, driving in one big circle or oval, hardly
qualifies as racing.......................

Jav

 

Nascar has some road tracks there not all ovals.